pcm_dither: pass an "end" pointer instead of a sample count

This is easier and more efficient to loop on, because only two
variables get modified (src and dest).

4 files changed, 16 insertions, 21 deletions

diff --git a/src/pcm_dither.c b/src/pcm_dither.c
index a75b07e5d..4811946c8 100644
--- a/src/pcm_dither.c
+++ b/src/pcm_dither.c
@@ -72,10 +72,9 @@ pcm_dither_sample_24_to_16(int32_t sample, struct pcm_dither *dither)
 
 void
 pcm_dither_24_to_16(struct pcm_dither *dither,
-		    int16_t *dest, const int32_t *src,
-		    unsigned num_samples)
+		    int16_t *dest, const int32_t *src, const int32_t *src_end)
 {
-	while (num_samples-- > 0)
+	while (src < src_end)
 		*dest++ = pcm_dither_sample_24_to_16(*src++, dither);
 }
 
@@ -87,9 +86,8 @@ pcm_dither_sample_32_to_16(int32_t sample, struct pcm_dither *dither)
 
 void
 pcm_dither_32_to_16(struct pcm_dither *dither,
-		    int16_t *dest, const int32_t *src,
-		    unsigned num_samples)
+		    int16_t *dest, const int32_t *src, const int32_t *src_end)
 {
-	while (num_samples-- > 0)
+	while (src < src_end)
 		*dest++ = pcm_dither_sample_32_to_16(*src++, dither);
 }
diff --git a/src/pcm_dither.h b/src/pcm_dither.h
index 5ba4d7bb4..046dea21e 100644
--- a/src/pcm_dither.h
+++ b/src/pcm_dither.h
@@ -36,12 +36,10 @@ pcm_dither_24_init(struct pcm_dither *dither)
 
 void
 pcm_dither_24_to_16(struct pcm_dither *dither,
-		    int16_t *dest, const int32_t *src,
-		    unsigned num_samples);
+		    int16_t *dest, const int32_t *src, const int32_t *src_end);
 
 void
 pcm_dither_32_to_16(struct pcm_dither *dither,
-		    int16_t *dest, const int32_t *src,
-		    unsigned num_samples);
+		    int16_t *dest, const int32_t *src, const int32_t *src_end);
 
 #endif
diff --git a/src/pcm_format.c b/src/pcm_format.c
index 21459f0f4..148cd70ed 100644
--- a/src/pcm_format.c
+++ b/src/pcm_format.c
@@ -35,18 +35,16 @@ pcm_convert_8_to_16(int16_t *out, const int8_t *in,
 
 static void
 pcm_convert_24_to_16(struct pcm_dither *dither,
-		     int16_t *out, const int32_t *in,
-		     unsigned num_samples)
+		     int16_t *out, const int32_t *in, const int32_t *in_end)
 {
-	pcm_dither_24_to_16(dither, out, in, num_samples);
+	pcm_dither_24_to_16(dither, out, in, in_end);
 }
 
 static void
 pcm_convert_32_to_16(struct pcm_dither *dither,
-		     int16_t *out, const int32_t *in,
-		     unsigned num_samples)
+		     int16_t *out, const int32_t *in, const int32_t *in_end)
 {
-	pcm_dither_32_to_16(dither, out, in, num_samples);
+	pcm_dither_32_to_16(dither, out, in, in_end);
 }
 
 static int32_t *
@@ -63,6 +61,7 @@ pcm_convert_to_16(struct pcm_buffer *buffer, struct pcm_dither *dither,
 		  enum sample_format src_format, const void *src,
 		  size_t src_size, size_t *dest_size_r)
 {
+	const void *src_end = (const char *)src + src_size;
 	unsigned num_samples;
 	int16_t *dest;
 	int32_t *dest32;
@@ -95,7 +94,7 @@ pcm_convert_to_16(struct pcm_buffer *buffer, struct pcm_dither *dither,
 		/* convert to 16 bit in-place */
 		*dest_size_r = num_samples * sizeof(*dest);
 		pcm_convert_24_to_16(dither, dest, dest32,
-				     num_samples);
+				     dest32 + num_samples);
 		return dest;
 
 	case SAMPLE_FORMAT_S24_P32:
@@ -105,7 +104,7 @@ pcm_convert_to_16(struct pcm_buffer *buffer, struct pcm_dither *dither,
 
 		pcm_convert_24_to_16(dither, dest,
 				     (const int32_t *)src,
-				     num_samples);
+				     (const int32_t *)src_end);
 		return dest;
 
 	case SAMPLE_FORMAT_S32:
@@ -115,7 +114,7 @@ pcm_convert_to_16(struct pcm_buffer *buffer, struct pcm_dither *dither,
 
 		pcm_convert_32_to_16(dither, dest,
 				     (const int32_t *)src,
-				     num_samples);
+				     (const int32_t *)src_end);
 		return dest;
 	}
 
diff --git a/test/test_pcm_dither.c b/test/test_pcm_dither.c
index 889c61ccd..44d105207 100644
--- a/test/test_pcm_dither.c
+++ b/test/test_pcm_dither.c
@@ -48,7 +48,7 @@ test_pcm_dither_24(void)
 
 	int16_t dest[N];
 
-	pcm_dither_24_to_16(&dither, dest, src, N);
+	pcm_dither_24_to_16(&dither, dest, src, src + N);
 
 	for (unsigned i = 0; i < N; ++i) {
 		g_assert_cmpint(dest[i], >=, (src[i] >> 8) - 8);
@@ -70,7 +70,7 @@ test_pcm_dither_32(void)
 
 	int16_t dest[N];
 
-	pcm_dither_32_to_16(&dither, dest, src, N);
+	pcm_dither_32_to_16(&dither, dest, src, src + N);
 
 	for (unsigned i = 0; i < N; ++i) {
 		g_assert_cmpint(dest[i], >=, (src[i] >> 16) - 8);