pcm: Fix the sound distortions for S24_3LE stream in pcm_softvol plugin

This patch fixes sound distortions in alsa-lib "softvol"
for S24_3LE sound stream, when softvol slider is not at 0.0dB
position.

Signed-off-by: CannibalZerg <cnb_zerg@yahoo.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

diff --git a/src/pcm/pcm_softvol.c b/src/pcm/pcm_softvol.c
index 637e5cb3ce7130d4d0b0bd8c3d9b06147ed80835..2c7c006efe3fd0b6ddfeb09c4483e330c930927c 100644 (file)
--- a/src/pcm/pcm_softvol.c
+++ b/src/pcm/pcm_softvol.c
@@ -107,7 +107,8 @@ static inline int MULTI_DIV_32x16(int a, unsigned short b)
        v.i = a;
        y.i = 0;
 #if __BYTE_ORDER == __LITTLE_ENDIAN
-       x.i = (unsigned int)v.s[0] * b;
+       x.i = (unsigned short)v.s[0];
+       x.i *= b;
        y.s[0] = x.s[1];
        y.i += (int)v.s[1] * b;
 #else
@@ -135,6 +136,23 @@ static inline int MULTI_DIV_int(int a, unsigned int b, int swap)
        return swap ? (int)bswap_32(fraction) : fraction;
 }
 
+/* always little endian */
+static inline int MULTI_DIV_24(int a, unsigned int b)
+{
+       unsigned int gain = b >> VOL_SCALE_SHIFT;
+       int fraction;
+       fraction = MULTI_DIV_32x16(a, b & VOL_SCALE_MASK);
+       if (gain) {
+               long long amp = (long long)a * gain + fraction;
+               if (amp > (int)0x7fffff)
+                       amp = (int)0x7fffff;
+               else if (amp < (int)0x800000)
+                       amp = (int)0x800000;
+               return (int)amp;
+       }
+       return fraction;
+}
+
 static inline short MULTI_DIV_short(short a, unsigned int b, int swap)
 {
        unsigned int gain = b >> VOL_SCALE_SHIFT;
@@ -223,7 +241,7 @@ static inline short MULTI_DIV_short(short a, unsigned int b, int swap)
                                tmp = src[0] |                          \
                                      (src[1] << 8) |                   \
                                      (((signed char *) src)[2] << 16); \
-                               tmp = MULTI_DIV_int(tmp, vol_scale, 0); \
+                               tmp = MULTI_DIV_24(tmp, vol_scale);     \
                                dst[0] = tmp;                           \
                                dst[1] = tmp >> 8;                      \
                                dst[2] = tmp >> 16;                     \