aboutsummaryrefslogblamecommitdiffstats
path: root/infrastructure/rhino1_7R1/src/org/mozilla/javascript/DToA.java
blob: ad2a68a96cd3e772d594e10c0608245ad1ef2a42 (plain) (tree)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271






















































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































                                                                                                                                                
/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Rhino code, released
 * May 6, 1999.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1997-1999
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Waldemar Horwat
 *   Roger Lawrence
 *   Attila Szegedi
 *
 * Alternatively, the contents of this file may be used under the terms of
 * the GNU General Public License Version 2 or later (the "GPL"), in which
 * case the provisions of the GPL are applicable instead of those above. If
 * you wish to allow use of your version of this file only under the terms of
 * the GPL and not to allow others to use your version of this file under the
 * MPL, indicate your decision by deleting the provisions above and replacing
 * them with the notice and other provisions required by the GPL. If you do
 * not delete the provisions above, a recipient may use your version of this
 * file under either the MPL or the GPL.
 *
 * ***** END LICENSE BLOCK ***** */

/****************************************************************
  *
  * The author of this software is David M. Gay.
  *
  * Copyright (c) 1991, 2000, 2001 by Lucent Technologies.
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose without fee is hereby granted, provided that this entire notice
  * is included in all copies of any software which is or includes a copy
  * or modification of this software and in all copies of the supporting
  * documentation for such software.
  *
  * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
  * WARRANTY.  IN PARTICULAR, NEITHER THE AUTHOR NOR LUCENT MAKES ANY
  * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
  * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
  *
  ***************************************************************/

package org.mozilla.javascript;

import java.math.BigInteger;

class DToA {


/* "-0.0000...(1073 zeros after decimal point)...0001\0" is the longest string that we could produce,
 * which occurs when printing -5e-324 in binary.  We could compute a better estimate of the size of
 * the output string and malloc fewer bytes depending on d and base, but why bother? */

    private static final int DTOBASESTR_BUFFER_SIZE = 1078;

    private static char BASEDIGIT(int digit) {
        return (char)((digit >= 10) ? 'a' - 10 + digit : '0' + digit);
    }

    static final int
        DTOSTR_STANDARD = 0,              /* Either fixed or exponential format; round-trip */
        DTOSTR_STANDARD_EXPONENTIAL = 1,  /* Always exponential format; round-trip */
        DTOSTR_FIXED = 2,                 /* Round to <precision> digits after the decimal point; exponential if number is large */
        DTOSTR_EXPONENTIAL = 3,           /* Always exponential format; <precision> significant digits */
        DTOSTR_PRECISION = 4;             /* Either fixed or exponential format; <precision> significant digits */


    private static final int Frac_mask = 0xfffff;
    private static final int Exp_shift = 20;
    private static final int Exp_msk1 = 0x100000;

    private static final long Frac_maskL = 0xfffffffffffffL;
    private static final int Exp_shiftL = 52;
    private static final long Exp_msk1L = 0x10000000000000L;

    private static final int Bias = 1023;
    private static final int P = 53;

    private static final int Exp_shift1 = 20;
    private static final int Exp_mask  = 0x7ff00000;
    private static final int Exp_mask_shifted = 0x7ff;
    private static final int Bndry_mask  = 0xfffff;
    private static final int Log2P = 1;

    private static final int Sign_bit = 0x80000000;
    private static final int Exp_11  = 0x3ff00000;
    private static final int Ten_pmax = 22;
    private static final int Quick_max = 14;
    private static final int Bletch = 0x10;
    private static final int Frac_mask1 = 0xfffff;
    private static final int Int_max = 14;
    private static final int n_bigtens = 5;


    private static final double tens[] = {
        1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9,
        1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19,
        1e20, 1e21, 1e22
    };

    private static final double bigtens[] = { 1e16, 1e32, 1e64, 1e128, 1e256 };

    private static int lo0bits(int y)
    {
        int k;
        int x = y;

        if ((x & 7) != 0) {
            if ((x & 1) != 0)
                return 0;
            if ((x & 2) != 0) {
                return 1;
            }
            return 2;
        }
        k = 0;
        if ((x & 0xffff) == 0) {
            k = 16;
            x >>>= 16;
        }
        if ((x & 0xff) == 0) {
            k += 8;
            x >>>= 8;
        }
        if ((x & 0xf) == 0) {
            k += 4;
            x >>>= 4;
        }
        if ((x & 0x3) == 0) {
            k += 2;
            x >>>= 2;
        }
        if ((x & 1) == 0) {
            k++;
            x >>>= 1;
            if ((x & 1) == 0)
                return 32;
        }
        return k;
    }

    /* Return the number (0 through 32) of most significant zero bits in x. */
    private static int hi0bits(int x)
    {
        int k = 0;

        if ((x & 0xffff0000) == 0) {
            k = 16;
            x <<= 16;
        }
        if ((x & 0xff000000) == 0) {
            k += 8;
            x <<= 8;
        }
        if ((x & 0xf0000000) == 0) {
            k += 4;
            x <<= 4;
        }
        if ((x & 0xc0000000) == 0) {
            k += 2;
            x <<= 2;
        }
        if ((x & 0x80000000) == 0) {
            k++;
            if ((x & 0x40000000) == 0)
                return 32;
        }
        return k;
    }

    private static void stuffBits(byte bits[], int offset, int val)
    {
        bits[offset] = (byte)(val >> 24);
        bits[offset + 1] = (byte)(val >> 16);
        bits[offset + 2] = (byte)(val >> 8);
        bits[offset + 3] = (byte)(val);
    }

    /* Convert d into the form b*2^e, where b is an odd integer.  b is the returned
     * Bigint and e is the returned binary exponent.  Return the number of significant
     * bits in b in bits.  d must be finite and nonzero. */
    private static BigInteger d2b(double d, int[] e, int[] bits)
    {
        byte dbl_bits[];
        int i, k, y, z, de;
        long dBits = Double.doubleToLongBits(d);
        int d0 = (int)(dBits >>> 32);
        int d1 = (int)(dBits);

        z = d0 & Frac_mask;
        d0 &= 0x7fffffff;   /* clear sign bit, which we ignore */

        if ((de = (d0 >>> Exp_shift)) != 0)
            z |= Exp_msk1;

        if ((y = d1) != 0) {
            dbl_bits = new byte[8];
            k = lo0bits(y);
            y >>>= k;
            if (k != 0) {
                stuffBits(dbl_bits, 4, y | z << (32 - k));
                z >>= k;
            }
            else
                stuffBits(dbl_bits, 4, y);
            stuffBits(dbl_bits, 0, z);
            i = (z != 0) ? 2 : 1;
        }
        else {
    //        JS_ASSERT(z);
            dbl_bits = new byte[4];
            k = lo0bits(z);
            z >>>= k;
            stuffBits(dbl_bits, 0, z);
            k += 32;
            i = 1;
        }
        if (de != 0) {
            e[0] = de - Bias - (P-1) + k;
            bits[0] = P - k;
        }
        else {
            e[0] = de - Bias - (P-1) + 1 + k;
            bits[0] = 32*i - hi0bits(z);
        }
        return new BigInteger(dbl_bits);
    }

    static String JS_dtobasestr(int base, double d)
    {
        if (!(2 <= base && base <= 36))
            throw new IllegalArgumentException("Bad base: "+base);

        /* Check for Infinity and NaN */
        if (Double.isNaN(d)) {
            return "NaN";
        } else if (Double.isInfinite(d)) {
            return (d > 0.0) ? "Infinity" : "-Infinity";
        } else if (d == 0) {
            // ALERT: should it distinguish -0.0 from +0.0 ?
            return "0";
        }

        boolean negative;
        if (d >= 0.0) {
            negative = false;
        } else {
            negative = true;
            d = -d;
        }

        /* Get the integer part of d including '-' sign. */
        String intDigits;

        double dfloor = Math.floor(d);
        long lfloor = (long)dfloor;
        if (lfloor == dfloor) {
            // int part fits long
            intDigits = Long.toString((negative) ? -lfloor : lfloor, base);
        } else {
            // BigInteger should be used
            long floorBits = Double.doubleToLongBits(dfloor);
            int exp = (int)(floorBits >> Exp_shiftL) & Exp_mask_shifted;
            long mantissa;
            if (exp == 0) {
                mantissa = (floorBits & Frac_maskL) << 1;
            } else {
                mantissa = (floorBits & Frac_maskL) | Exp_msk1L;
            }
            if (negative) {
                mantissa = -mantissa;
            }
            exp -= 1075;
            BigInteger x = BigInteger.valueOf(mantissa);
            if (exp > 0) {
                x = x.shiftLeft(exp);
            } else if (exp < 0) {
                x = x.shiftRight(-exp);
            }
            intDigits = x.toString(base);
        }

        if (d == dfloor) {
            // No fraction part
            return intDigits;
        } else {
            /* We have a fraction. */

            char[] buffer;       /* The output string */
            int p;               /* index to current position in the buffer */
            int digit;
            double df;           /* The fractional part of d */
            BigInteger b;

            buffer = new char[DTOBASESTR_BUFFER_SIZE];
            p = 0;
            df = d - dfloor;

            long dBits = Double.doubleToLongBits(d);
            int word0 = (int)(dBits >> 32);
            int word1 = (int)(dBits);

            int[] e = new int[1];
            int[] bbits = new int[1];

            b = d2b(df, e, bbits);
//            JS_ASSERT(e < 0);
            /* At this point df = b * 2^e.  e must be less than zero because 0 < df < 1. */

            int s2 = -(word0 >>> Exp_shift1 & Exp_mask >> Exp_shift1);
            if (s2 == 0)
                s2 = -1;
            s2 += Bias + P;
            /* 1/2^s2 = (nextDouble(d) - d)/2 */
//            JS_ASSERT(-s2 < e);
            BigInteger mlo = BigInteger.valueOf(1);
            BigInteger mhi = mlo;
            if ((word1 == 0) && ((word0 & Bndry_mask) == 0)
                && ((word0 & (Exp_mask & Exp_mask << 1)) != 0)) {
                /* The special case.  Here we want to be within a quarter of the last input
                   significant digit instead of one half of it when the output string's value is less than d.  */
                s2 += Log2P;
                mhi = BigInteger.valueOf(1<<Log2P);
            }

            b = b.shiftLeft(e[0] + s2);
            BigInteger s = BigInteger.valueOf(1);
            s = s.shiftLeft(s2);
            /* At this point we have the following:
             *   s = 2^s2;
             *   1 > df = b/2^s2 > 0;
             *   (d - prevDouble(d))/2 = mlo/2^s2;
             *   (nextDouble(d) - d)/2 = mhi/2^s2. */
            BigInteger bigBase = BigInteger.valueOf(base);

            boolean done = false;
            do {
                b = b.multiply(bigBase);
                BigInteger[] divResult = b.divideAndRemainder(s);
                b = divResult[1];
                digit = (char)(divResult[0].intValue());
                if (mlo == mhi)
                    mlo = mhi = mlo.multiply(bigBase);
                else {
                    mlo = mlo.multiply(bigBase);
                    mhi = mhi.multiply(bigBase);
                }

                /* Do we yet have the shortest string that will round to d? */
                int j = b.compareTo(mlo);
                /* j is b/2^s2 compared with mlo/2^s2. */
                BigInteger delta = s.subtract(mhi);
                int j1 = (delta.signum() <= 0) ? 1 : b.compareTo(delta);
                /* j1 is b/2^s2 compared with 1 - mhi/2^s2. */
                if (j1 == 0 && ((word1 & 1) == 0)) {
                    if (j > 0)
                        digit++;
                    done = true;
                } else
                if (j < 0 || (j == 0 && ((word1 & 1) == 0))) {
                    if (j1 > 0) {
                        /* Either dig or dig+1 would work here as the least significant digit.
                           Use whichever would produce an output value closer to d. */
                        b = b.shiftLeft(1);
                        j1 = b.compareTo(s);
                        if (j1 > 0) /* The even test (|| (j1 == 0 && (digit & 1))) is not here because it messes up odd base output
                                     * such as 3.5 in base 3.  */
                            digit++;
                    }
                    done = true;
                } else if (j1 > 0) {
                    digit++;
                    done = true;
                }
//                JS_ASSERT(digit < (uint32)base);
                buffer[p++] = BASEDIGIT(digit);
            } while (!done);

            StringBuffer sb = new StringBuffer(intDigits.length() + 1 + p);
            sb.append(intDigits);
            sb.append('.');
            sb.append(buffer, 0, p);
            return sb.toString();
        }

    }

    /* dtoa for IEEE arithmetic (dmg): convert double to ASCII string.
     *
     * Inspired by "How to Print Floating-Point Numbers Accurately" by
     * Guy L. Steele, Jr. and Jon L. White [Proc. ACM SIGPLAN '90, pp. 92-101].
     *
     * Modifications:
     *  1. Rather than iterating, we use a simple numeric overestimate
     *     to determine k = floor(log10(d)).  We scale relevant
     *     quantities using O(log2(k)) rather than O(k) multiplications.
     *  2. For some modes > 2 (corresponding to ecvt and fcvt), we don't
     *     try to generate digits strictly left to right.  Instead, we
     *     compute with fewer bits and propagate the carry if necessary
     *     when rounding the final digit up.  This is often faster.
     *  3. Under the assumption that input will be rounded nearest,
     *     mode 0 renders 1e23 as 1e23 rather than 9.999999999999999e22.
     *     That is, we allow equality in stopping tests when the
     *     round-nearest rule will give the same floating-point value
     *     as would satisfaction of the stopping test with strict
     *     inequality.
     *  4. We remove common factors of powers of 2 from relevant
     *     quantities.
     *  5. When converting floating-point integers less than 1e16,
     *     we use floating-point arithmetic rather than resorting
     *     to multiple-precision integers.
     *  6. When asked to produce fewer than 15 digits, we first try
     *     to get by with floating-point arithmetic; we resort to
     *     multiple-precision integer arithmetic only if we cannot
     *     guarantee that the floating-point calculation has given
     *     the correctly rounded result.  For k requested digits and
     *     "uniformly" distributed input, the probability is
     *     something like 10^(k-15) that we must resort to the Long
     *     calculation.
     */

    static int word0(double d)
    {
        long dBits = Double.doubleToLongBits(d);
        return (int)(dBits >> 32);
    }

    static double setWord0(double d, int i)
    {
        long dBits = Double.doubleToLongBits(d);
        dBits = ((long)i << 32) | (dBits & 0x0FFFFFFFFL);
        return Double.longBitsToDouble(dBits);
    }

    static int word1(double d)
    {
        long dBits = Double.doubleToLongBits(d);
        return (int)(dBits);
    }

    /* Return b * 5^k.  k must be nonnegative. */
    // XXXX the C version built a cache of these
    static BigInteger pow5mult(BigInteger b, int k)
    {
        return b.multiply(BigInteger.valueOf(5).pow(k));
    }

    static boolean roundOff(StringBuffer buf)
    {
        int i = buf.length();
        while (i != 0) {
            --i;
            char c = buf.charAt(i);
            if (c != '9') {
                buf.setCharAt(i, (char)(c + 1));
                buf.setLength(i + 1);
                return false;
            }
        }
        buf.setLength(0);
        return true;
    }

    /* Always emits at least one digit. */
    /* If biasUp is set, then rounding in modes 2 and 3 will round away from zero
     * when the number is exactly halfway between two representable values.  For example,
     * rounding 2.5 to zero digits after the decimal point will return 3 and not 2.
     * 2.49 will still round to 2, and 2.51 will still round to 3. */
    /* bufsize should be at least 20 for modes 0 and 1.  For the other modes,
     * bufsize should be two greater than the maximum number of output characters expected. */
    static int
    JS_dtoa(double d, int mode, boolean biasUp, int ndigits,
                    boolean[] sign, StringBuffer buf)
    {
        /*  Arguments ndigits, decpt, sign are similar to those
            of ecvt and fcvt; trailing zeros are suppressed from
            the returned string.  If not null, *rve is set to point
            to the end of the return value.  If d is +-Infinity or NaN,
            then *decpt is set to 9999.

            mode:
            0 ==> shortest string that yields d when read in
            and rounded to nearest.
            1 ==> like 0, but with Steele & White stopping rule;
            e.g. with IEEE P754 arithmetic , mode 0 gives
            1e23 whereas mode 1 gives 9.999999999999999e22.
            2 ==> max(1,ndigits) significant digits.  This gives a
            return value similar to that of ecvt, except
            that trailing zeros are suppressed.
            3 ==> through ndigits past the decimal point.  This
            gives a return value similar to that from fcvt,
            except that trailing zeros are suppressed, and
            ndigits can be negative.
            4-9 should give the same return values as 2-3, i.e.,
            4 <= mode <= 9 ==> same return as mode
            2 + (mode & 1).  These modes are mainly for
            debugging; often they run slower but sometimes
            faster than modes 2-3.
            4,5,8,9 ==> left-to-right digit generation.
            6-9 ==> don't try fast floating-point estimate
            (if applicable).

            Values of mode other than 0-9 are treated as mode 0.

            Sufficient space is allocated to the return value
            to hold the suppressed trailing zeros.
        */

        int b2, b5, i, ieps, ilim, ilim0, ilim1,
            j, j1, k, k0, m2, m5, s2, s5;
        char dig;
        long L;
        long x;
        BigInteger b, b1, delta, mlo, mhi, S;
        int[] be = new int[1];
        int[] bbits = new int[1];
        double d2, ds, eps;
        boolean spec_case, denorm, k_check, try_quick, leftright;

        if ((word0(d) & Sign_bit) != 0) {
            /* set sign for everything, including 0's and NaNs */
            sign[0] = true;
            // word0(d) &= ~Sign_bit;  /* clear sign bit */
            d = setWord0(d, word0(d) & ~Sign_bit);
        }
        else
            sign[0] = false;

        if ((word0(d) & Exp_mask) == Exp_mask) {
            /* Infinity or NaN */
            buf.append(((word1(d) == 0) && ((word0(d) & Frac_mask) == 0)) ? "Infinity" : "NaN");
            return 9999;
        }
        if (d == 0) {
//          no_digits:
            buf.setLength(0);
            buf.append('0');        /* copy "0" to buffer */
            return 1;
        }

        b = d2b(d, be, bbits);
        if ((i = (word0(d) >>> Exp_shift1 & (Exp_mask>>Exp_shift1))) != 0) {
            d2 = setWord0(d, (word0(d) & Frac_mask1) | Exp_11);
            /* log(x)   ~=~ log(1.5) + (x-1.5)/1.5
             * log10(x)  =  log(x) / log(10)
             *      ~=~ log(1.5)/log(10) + (x-1.5)/(1.5*log(10))
             * log10(d) = (i-Bias)*log(2)/log(10) + log10(d2)
             *
             * This suggests computing an approximation k to log10(d) by
             *
             * k = (i - Bias)*0.301029995663981
             *  + ( (d2-1.5)*0.289529654602168 + 0.176091259055681 );
             *
             * We want k to be too large rather than too small.
             * The error in the first-order Taylor series approximation
             * is in our favor, so we just round up the constant enough
             * to compensate for any error in the multiplication of
             * (i - Bias) by 0.301029995663981; since |i - Bias| <= 1077,
             * and 1077 * 0.30103 * 2^-52 ~=~ 7.2e-14,
             * adding 1e-13 to the constant term more than suffices.
             * Hence we adjust the constant term to 0.1760912590558.
             * (We could get a more accurate k by invoking log10,
             *  but this is probably not worthwhile.)
             */
            i -= Bias;
            denorm = false;
        }
        else {
            /* d is denormalized */
            i = bbits[0] + be[0] + (Bias + (P-1) - 1);
            x = (i > 32) ? word0(d) << (64 - i) | word1(d) >>> (i - 32) : word1(d) << (32 - i);
//            d2 = x;
//            word0(d2) -= 31*Exp_msk1; /* adjust exponent */
            d2 = setWord0(x, word0(x) - 31*Exp_msk1);
            i -= (Bias + (P-1) - 1) + 1;
            denorm = true;
        }
        /* At this point d = f*2^i, where 1 <= f < 2.  d2 is an approximation of f. */
        ds = (d2-1.5)*0.289529654602168 + 0.1760912590558 + i*0.301029995663981;
        k = (int)ds;
        if (ds < 0.0 && ds != k)
            k--;    /* want k = floor(ds) */
        k_check = true;
        if (k >= 0 && k <= Ten_pmax) {
            if (d < tens[k])
                k--;
            k_check = false;
        }
        /* At this point floor(log10(d)) <= k <= floor(log10(d))+1.
           If k_check is zero, we're guaranteed that k = floor(log10(d)). */
        j = bbits[0] - i - 1;
        /* At this point d = b/2^j, where b is an odd integer. */
        if (j >= 0) {
            b2 = 0;
            s2 = j;
        }
        else {
            b2 = -j;
            s2 = 0;
        }
        if (k >= 0) {
            b5 = 0;
            s5 = k;
            s2 += k;
        }
        else {
            b2 -= k;
            b5 = -k;
            s5 = 0;
        }
        /* At this point d/10^k = (b * 2^b2 * 5^b5) / (2^s2 * 5^s5), where b is an odd integer,
           b2 >= 0, b5 >= 0, s2 >= 0, and s5 >= 0. */
        if (mode < 0 || mode > 9)
            mode = 0;
        try_quick = true;
        if (mode > 5) {
            mode -= 4;
            try_quick = false;
        }
        leftright = true;
        ilim = ilim1 = 0;
        switch(mode) {
            case 0:
            case 1:
                ilim = ilim1 = -1;
                i = 18;
                ndigits = 0;
                break;
            case 2:
                leftright = false;
                /* no break */
            case 4:
                if (ndigits <= 0)
                    ndigits = 1;
                ilim = ilim1 = i = ndigits;
                break;
            case 3:
                leftright = false;
                /* no break */
            case 5:
                i = ndigits + k + 1;
                ilim = i;
                ilim1 = i - 1;
                if (i <= 0)
                    i = 1;
        }
        /* ilim is the maximum number of significant digits we want, based on k and ndigits. */
        /* ilim1 is the maximum number of significant digits we want, based on k and ndigits,
           when it turns out that k was computed too high by one. */

        boolean fast_failed = false;
        if (ilim >= 0 && ilim <= Quick_max && try_quick) {

            /* Try to get by with floating-point arithmetic. */

            i = 0;
            d2 = d;
            k0 = k;
            ilim0 = ilim;
            ieps = 2; /* conservative */
            /* Divide d by 10^k, keeping track of the roundoff error and avoiding overflows. */
            if (k > 0) {
                ds = tens[k&0xf];
                j = k >> 4;
                if ((j & Bletch) != 0) {
                    /* prevent overflows */
                    j &= Bletch - 1;
                    d /= bigtens[n_bigtens-1];
                    ieps++;
                }
                for(; (j != 0); j >>= 1, i++)
                    if ((j & 1) != 0) {
                        ieps++;
                        ds *= bigtens[i];
                    }
                d /= ds;
            }
            else if ((j1 = -k) != 0) {
                d *= tens[j1 & 0xf];
                for(j = j1 >> 4; (j != 0); j >>= 1, i++)
                    if ((j & 1) != 0) {
                        ieps++;
                        d *= bigtens[i];
                    }
            }
            /* Check that k was computed correctly. */
            if (k_check && d < 1.0 && ilim > 0) {
                if (ilim1 <= 0)
                    fast_failed = true;
                else {
                    ilim = ilim1;
                    k--;
                    d *= 10.;
                    ieps++;
                }
            }
            /* eps bounds the cumulative error. */
//            eps = ieps*d + 7.0;
//            word0(eps) -= (P-1)*Exp_msk1;
            eps = ieps*d + 7.0;
            eps = setWord0(eps, word0(eps) - (P-1)*Exp_msk1);
            if (ilim == 0) {
                S = mhi = null;
                d -= 5.0;
                if (d > eps) {
                    buf.append('1');
                    k++;
                    return k + 1;
                }
                if (d < -eps) {
                    buf.setLength(0);
                    buf.append('0');        /* copy "0" to buffer */
                    return 1;
                }
                fast_failed = true;
            }
            if (!fast_failed) {
                fast_failed = true;
                if (leftright) {
                    /* Use Steele & White method of only
                     * generating digits needed.
                     */
                    eps = 0.5/tens[ilim-1] - eps;
                    for(i = 0;;) {
                        L = (long)d;
                        d -= L;
                        buf.append((char)('0' + L));
                        if (d < eps) {
                            return k + 1;
                        }
                        if (1.0 - d < eps) {
//                            goto bump_up;
                                char lastCh;
                                while (true) {
                                    lastCh = buf.charAt(buf.length() - 1);
                                    buf.setLength(buf.length() - 1);
                                    if (lastCh != '9') break;
                                    if (buf.length() == 0) {
                                        k++;
                                        lastCh = '0';
                                        break;
                                    }
                                }
                                buf.append((char)(lastCh + 1));
                                return k + 1;
                        }
                        if (++i >= ilim)
                            break;
                        eps *= 10.0;
                        d *= 10.0;
                    }
                }
                else {
                    /* Generate ilim digits, then fix them up. */
                    eps *= tens[ilim-1];
                    for(i = 1;; i++, d *= 10.0) {
                        L = (long)d;
                        d -= L;
                        buf.append((char)('0' + L));
                        if (i == ilim) {
                            if (d > 0.5 + eps) {
//                                goto bump_up;
                                char lastCh;
                                while (true) {
                                    lastCh = buf.charAt(buf.length() - 1);
                                    buf.setLength(buf.length() - 1);
                                    if (lastCh != '9') break;
                                    if (buf.length() == 0) {
                                        k++;
                                        lastCh = '0';
                                        break;
                                    }
                                }
                                buf.append((char)(lastCh + 1));
                                return k + 1;
                            }
                            else
                                if (d < 0.5 - eps) {
                                    stripTrailingZeroes(buf);                                    
//                                    while(*--s == '0') ;
//                                    s++;
                                    return k + 1;
                                }
                            break;
                        }
                    }
                }
            }
            if (fast_failed) {
                buf.setLength(0);
                d = d2;
                k = k0;
                ilim = ilim0;
            }
        }

        /* Do we have a "small" integer? */

        if (be[0] >= 0 && k <= Int_max) {
            /* Yes. */
            ds = tens[k];
            if (ndigits < 0 && ilim <= 0) {
                S = mhi = null;
                if (ilim < 0 || d < 5*ds || (!biasUp && d == 5*ds)) {
                    buf.setLength(0);
                    buf.append('0');        /* copy "0" to buffer */
                    return 1;
                }
                buf.append('1');
                k++;
                return k + 1;
            }
            for(i = 1;; i++) {
                L = (long) (d / ds);
                d -= L*ds;
                buf.append((char)('0' + L));
                if (i == ilim) {
                    d += d;
                    if ((d > ds) || (d == ds && (((L & 1) != 0) || biasUp))) {
//                    bump_up:
//                        while(*--s == '9')
//                            if (s == buf) {
//                                k++;
//                                *s = '0';
//                                break;
//                            }
//                        ++*s++;
                        char lastCh;
                        while (true) {
                            lastCh = buf.charAt(buf.length() - 1);
                            buf.setLength(buf.length() - 1);
                            if (lastCh != '9') break;
                            if (buf.length() == 0) {
                                k++;
                                lastCh = '0';
                                break;
                            }
                        }
                        buf.append((char)(lastCh + 1));
                    }
                    break;
                }
                d *= 10.0;
                if (d == 0)
                    break;
            }
            return k + 1;
        }

        m2 = b2;
        m5 = b5;
        mhi = mlo = null;
        if (leftright) {
            if (mode < 2) {
                i = (denorm) ? be[0] + (Bias + (P-1) - 1 + 1) : 1 + P - bbits[0];
                /* i is 1 plus the number of trailing zero bits in d's significand. Thus,
                   (2^m2 * 5^m5) / (2^(s2+i) * 5^s5) = (1/2 lsb of d)/10^k. */
            }
            else {
                j = ilim - 1;
                if (m5 >= j)
                    m5 -= j;
                else {
                    s5 += j -= m5;
                    b5 += j;
                    m5 = 0;
                }
                if ((i = ilim) < 0) {
                    m2 -= i;
                    i = 0;
                }
                /* (2^m2 * 5^m5) / (2^(s2+i) * 5^s5) = (1/2 * 10^(1-ilim))/10^k. */
            }
            b2 += i;
            s2 += i;
            mhi = BigInteger.valueOf(1);
            /* (mhi * 2^m2 * 5^m5) / (2^s2 * 5^s5) = one-half of last printed (when mode >= 2) or
               input (when mode < 2) significant digit, divided by 10^k. */
        }
        /* We still have d/10^k = (b * 2^b2 * 5^b5) / (2^s2 * 5^s5).  Reduce common factors in
           b2, m2, and s2 without changing the equalities. */
        if (m2 > 0 && s2 > 0) {
            i = (m2 < s2) ? m2 : s2;
            b2 -= i;
            m2 -= i;
            s2 -= i;
        }

        /* Fold b5 into b and m5 into mhi. */
        if (b5 > 0) {
            if (leftright) {
                if (m5 > 0) {
                    mhi = pow5mult(mhi, m5);
                    b1 = mhi.multiply(b);
                    b = b1;
                }
                if ((j = b5 - m5) != 0)
                    b = pow5mult(b, j);
            }
            else
                b = pow5mult(b, b5);
        }
        /* Now we have d/10^k = (b * 2^b2) / (2^s2 * 5^s5) and
           (mhi * 2^m2) / (2^s2 * 5^s5) = one-half of last printed or input significant digit, divided by 10^k. */

        S = BigInteger.valueOf(1);
        if (s5 > 0)
            S = pow5mult(S, s5);
        /* Now we have d/10^k = (b * 2^b2) / (S * 2^s2) and
           (mhi * 2^m2) / (S * 2^s2) = one-half of last printed or input significant digit, divided by 10^k. */

        /* Check for special case that d is a normalized power of 2. */
        spec_case = false;
        if (mode < 2) {
            if ( (word1(d) == 0) && ((word0(d) & Bndry_mask) == 0)
                && ((word0(d) & (Exp_mask & Exp_mask << 1)) != 0)
                ) {
                /* The special case.  Here we want to be within a quarter of the last input
                   significant digit instead of one half of it when the decimal output string's value is less than d.  */
                b2 += Log2P;
                s2 += Log2P;
                spec_case = true;
            }
        }

        /* Arrange for convenient computation of quotients:
         * shift left if necessary so divisor has 4 leading 0 bits.
         *
         * Perhaps we should just compute leading 28 bits of S once
         * and for all and pass them and a shift to quorem, so it
         * can do shifts and ors to compute the numerator for q.
         */
        byte [] S_bytes = S.toByteArray();
        int S_hiWord = 0;
        for (int idx = 0; idx < 4; idx++) {
            S_hiWord = (S_hiWord << 8);
            if (idx < S_bytes.length)
                S_hiWord |= (S_bytes[idx] & 0xFF);
        }
        if ((i = (((s5 != 0) ? 32 - hi0bits(S_hiWord) : 1) + s2) & 0x1f) != 0)
            i = 32 - i;
        /* i is the number of leading zero bits in the most significant word of S*2^s2. */
        if (i > 4) {
            i -= 4;
            b2 += i;
            m2 += i;
            s2 += i;
        }
        else if (i < 4) {
            i += 28;
            b2 += i;
            m2 += i;
            s2 += i;
        }
        /* Now S*2^s2 has exactly four leading zero bits in its most significant word. */
        if (b2 > 0)
            b = b.shiftLeft(b2);
        if (s2 > 0)
            S = S.shiftLeft(s2);
        /* Now we have d/10^k = b/S and
           (mhi * 2^m2) / S = maximum acceptable error, divided by 10^k. */
        if (k_check) {
            if (b.compareTo(S) < 0) {
                k--;
                b = b.multiply(BigInteger.valueOf(10));  /* we botched the k estimate */
                if (leftright)
                    mhi = mhi.multiply(BigInteger.valueOf(10));
                ilim = ilim1;
            }
        }
        /* At this point 1 <= d/10^k = b/S < 10. */

        if (ilim <= 0 && mode > 2) {
            /* We're doing fixed-mode output and d is less than the minimum nonzero output in this mode.
               Output either zero or the minimum nonzero output depending on which is closer to d. */
            if ((ilim < 0 )
                    || ((i = b.compareTo(S = S.multiply(BigInteger.valueOf(5)))) < 0)
                    || ((i == 0 && !biasUp))) {
            /* Always emit at least one digit.  If the number appears to be zero
               using the current mode, then emit one '0' digit and set decpt to 1. */
            /*no_digits:
                k = -1 - ndigits;
                goto ret; */
                buf.setLength(0);
                buf.append('0');        /* copy "0" to buffer */
                return 1;
//                goto no_digits;
            }
//        one_digit:
            buf.append('1');
            k++;
            return k + 1;
        }
        if (leftright) {
            if (m2 > 0)
                mhi = mhi.shiftLeft(m2);

            /* Compute mlo -- check for special case
             * that d is a normalized power of 2.
             */

            mlo = mhi;
            if (spec_case) {
                mhi = mlo;
                mhi = mhi.shiftLeft(Log2P);
            }
            /* mlo/S = maximum acceptable error, divided by 10^k, if the output is less than d. */
            /* mhi/S = maximum acceptable error, divided by 10^k, if the output is greater than d. */

            for(i = 1;;i++) {
                BigInteger[] divResult = b.divideAndRemainder(S);
                b = divResult[1];
                dig = (char)(divResult[0].intValue() + '0');
                /* Do we yet have the shortest decimal string
                 * that will round to d?
                 */
                j = b.compareTo(mlo);
                /* j is b/S compared with mlo/S. */
                delta = S.subtract(mhi);
                j1 = (delta.signum() <= 0) ? 1 : b.compareTo(delta);
                /* j1 is b/S compared with 1 - mhi/S. */
                if ((j1 == 0) && (mode == 0) && ((word1(d) & 1) == 0)) {
                    if (dig == '9') {
                        buf.append('9');
                        if (roundOff(buf)) {
                            k++;
                            buf.append('1');
                        }
                        return k + 1;
//                        goto round_9_up;
                    }
                    if (j > 0)
                        dig++;
                    buf.append(dig);
                    return k + 1;
                }
                if ((j < 0)
                        || ((j == 0)
                            && (mode == 0)
                            && ((word1(d) & 1) == 0)
                    )) {
                    if (j1 > 0) {
                        /* Either dig or dig+1 would work here as the least significant decimal digit.
                           Use whichever would produce a decimal value closer to d. */
                        b = b.shiftLeft(1);
                        j1 = b.compareTo(S);
                        if (((j1 > 0) || (j1 == 0 && (((dig & 1) == 1) || biasUp)))
                            && (dig++ == '9')) {
                                buf.append('9');
                                if (roundOff(buf)) {
                                    k++;
                                    buf.append('1');
                                }
                                return k + 1;
//                                goto round_9_up;
                        }
                    }
                    buf.append(dig);
                    return k + 1;
                }
                if (j1 > 0) {
                    if (dig == '9') { /* possible if i == 1 */
//                    round_9_up:
//                        *s++ = '9';
//                        goto roundoff;
                        buf.append('9');
                        if (roundOff(buf)) {
                            k++;
                            buf.append('1');
                        }
                        return k + 1;
                    }
                    buf.append((char)(dig + 1));
                    return k + 1;
                }
                buf.append(dig);
                if (i == ilim)
                    break;
                b = b.multiply(BigInteger.valueOf(10));
                if (mlo == mhi)
                    mlo = mhi = mhi.multiply(BigInteger.valueOf(10));
                else {
                    mlo = mlo.multiply(BigInteger.valueOf(10));
                    mhi = mhi.multiply(BigInteger.valueOf(10));
                }
            }
        }
        else
            for(i = 1;; i++) {
//                (char)(dig = quorem(b,S) + '0');
                BigInteger[] divResult = b.divideAndRemainder(S);
                b = divResult[1];
                dig = (char)(divResult[0].intValue() + '0');
                buf.append(dig);
                if (i >= ilim)
                    break;
                b = b.multiply(BigInteger.valueOf(10));
            }

        /* Round off last digit */

        b = b.shiftLeft(1);
        j = b.compareTo(S);
        if ((j > 0) || (j == 0 && (((dig & 1) == 1) || biasUp))) {
//        roundoff:
//            while(*--s == '9')
//                if (s == buf) {
//                    k++;
//                    *s++ = '1';
//                    goto ret;
//                }
//            ++*s++;
            if (roundOff(buf)) {
                k++;
                buf.append('1');
                return k + 1;
            }
        }
        else {
            stripTrailingZeroes(buf);
//            while(*--s == '0') ;
//            s++;
        }
//      ret:
//        Bfree(S);
//        if (mhi) {
//            if (mlo && mlo != mhi)
//                Bfree(mlo);
//            Bfree(mhi);
//        }
//      ret1:
//        Bfree(b);
//        JS_ASSERT(s < buf + bufsize);
        return k + 1;
    }

    private static void 
    stripTrailingZeroes(StringBuffer buf)
    {
//      while(*--s == '0') ;
//      s++;
        int bl = buf.length();
        while(bl-->0 && buf.charAt(bl) == '0') {
          // empty
        }
        buf.setLength(bl + 1);
    }

    /* Mapping of JSDToStrMode -> JS_dtoa mode */
    private static final int dtoaModes[] = {
        0,   /* DTOSTR_STANDARD */
        0,   /* DTOSTR_STANDARD_EXPONENTIAL, */
        3,   /* DTOSTR_FIXED, */
        2,   /* DTOSTR_EXPONENTIAL, */
        2};  /* DTOSTR_PRECISION */

    static void
    JS_dtostr(StringBuffer buffer, int mode, int precision, double d)
    {
        int decPt;                                    /* Position of decimal point relative to first digit returned by JS_dtoa */
        boolean[] sign = new boolean[1];            /* true if the sign bit was set in d */
        int nDigits;                                /* Number of significand digits returned by JS_dtoa */

//        JS_ASSERT(bufferSize >= (size_t)(mode <= DTOSTR_STANDARD_EXPONENTIAL ? DTOSTR_STANDARD_BUFFER_SIZE :
//                DTOSTR_VARIABLE_BUFFER_SIZE(precision)));

        if (mode == DTOSTR_FIXED && (d >= 1e21 || d <= -1e21))
            mode = DTOSTR_STANDARD; /* Change mode here rather than below because the buffer may not be large enough to hold a large integer. */

        decPt = JS_dtoa(d, dtoaModes[mode], mode >= DTOSTR_FIXED, precision, sign, buffer);
        nDigits = buffer.length();

        /* If Infinity, -Infinity, or NaN, return the string regardless of the mode. */
        if (decPt != 9999) {
            boolean exponentialNotation = false;
            int minNDigits = 0;         /* Minimum number of significand digits required by mode and precision */
            int p;

            switch (mode) {
                case DTOSTR_STANDARD:
                    if (decPt < -5 || decPt > 21)
                        exponentialNotation = true;
                    else
                        minNDigits = decPt;
                    break;

                case DTOSTR_FIXED:
                    if (precision >= 0)
                        minNDigits = decPt + precision;
                    else
                        minNDigits = decPt;
                    break;

                case DTOSTR_EXPONENTIAL:
//                    JS_ASSERT(precision > 0);
                    minNDigits = precision;
                    /* Fall through */
                case DTOSTR_STANDARD_EXPONENTIAL:
                    exponentialNotation = true;
                    break;

                case DTOSTR_PRECISION:
//                    JS_ASSERT(precision > 0);
                    minNDigits = precision;
                    if (decPt < -5 || decPt > precision)
                        exponentialNotation = true;
                    break;
            }

            /* If the number has fewer than minNDigits, pad it with zeros at the end */
            if (nDigits < minNDigits) {
                p = minNDigits;
                nDigits = minNDigits;
                do {
                    buffer.append('0');
                } while (buffer.length() != p);
            }

            if (exponentialNotation) {
                /* Insert a decimal point if more than one significand digit */
                if (nDigits != 1) {
                    buffer.insert(1, '.');
                }
                buffer.append('e');
                if ((decPt - 1) >= 0)
                    buffer.append('+');
                buffer.append(decPt - 1);
//                JS_snprintf(numEnd, bufferSize - (numEnd - buffer), "e%+d", decPt-1);
            } else if (decPt != nDigits) {
                /* Some kind of a fraction in fixed notation */
//                JS_ASSERT(decPt <= nDigits);
                if (decPt > 0) {
                    /* dd...dd . dd...dd */
                    buffer.insert(decPt, '.');
                } else {
                    /* 0 . 00...00dd...dd */
                    for (int i = 0; i < 1 - decPt; i++)
                        buffer.insert(0, '0');
                    buffer.insert(1, '.');
                }
            }
        }

        /* If negative and neither -0.0 nor NaN, output a leading '-'. */
        if (sign[0] &&
                !(word0(d) == Sign_bit && word1(d) == 0) &&
                !((word0(d) & Exp_mask) == Exp_mask &&
                  ((word1(d) != 0) || ((word0(d) & Frac_mask) != 0)))) {
            buffer.insert(0, '-');
        }
    }

}