At Wed, 29 May 2019 10:20:38 +0300,
Andreas Gustafsson wrote:
> > Now, you omit the most critical bit: what would you name the thing? :)
> > From "the proper way to do audio scaling" I infer that AUDIO_SCALEDOWN
> > (or however that was spelled) should be ok, shouldn't it?
>
> I'm not fussy about the naming, just about the math :) AUDIO_SCALEDOWN
> works for me, but I'm open to alternatives.
Thank you, riastradh@ and gson@!
AUDIO_SCALEDOWN is self explaining name and good for me, too.
I also think floor() is good for this purpose and truncate() is
also acceptable for alternate.
How about this one?
--- sys/dev/audio/audio.c
+++ sys/dev/audio/audio.c
@@ -458,6 +458,28 @@ audio_track_bufstat(audio_track_t *track, struct
audio_track_debugbuf *buf)
#define SPECIFIED(x) ((x) != ~0)
#define SPECIFIED_CH(x) ((x) != (u_char)~0)
+/*
+ * AUDIO_SCALEDOWN()
+ * This macro should be used for audio wave data only.
+ *
+ * The arithmetic shift right (ASR) (in other words, floor()) is good for
+ * this purpose, and will be faster than division on the most platform.
+ * The division (in other words, truncate()) is not so bad alternate for
+ * this purpose, and will be fast enough.
+ * (Using ASR is 1.9 times faster than division on my amd64, and 1.3 times
+ * faster on my m68k. -- isaki 201801.)
+ *
+ * However, the right shift operator ('>>') for negative integer is
+ * "implementation defined" behavior in C (note that it's not "undefined"
+ * behavior). So only if implementation defines '>>' as ASR, we use it.
+ */
+#if defined(__GNUC__)
+/* gcc defines '>>' as ASR. */
+#define AUDIO_SCALEDOWN(value, bits) ((value) >> (bits))
+#else
+#define AUDIO_SCALEDOWN(value, bits) ((value) / (1 << (bits)))
+#endif
+
/* Device timeout in msec */
#define AUDIO_TIMEOUT (3000)
@@ -3194,11 +3216,7 @@ audio_track_chvol(audio_filter_arg_t *arg)
for (ch = 0; ch < channels; ch++) {
aint2_t val;
val = *s++;
-#if defined(AUDIO_USE_C_IMPLEMENTATION_DEFINED_BEHAVIOR) && defined(__GNUC__)
- val = val * ch_volume[ch] >> 8;
-#else
- val = val * ch_volume[ch] / 256;
-#endif
+ val = AUDIO_SCALEDOWN(val * ch_volume[ch], 8);
*d++ = (aint_t)val;
}
}
@@ -3220,11 +3238,7 @@ audio_track_chmix_mixLR(audio_filter_arg_t *arg)
d = arg->dst;
for (i = 0; i < arg->count; i++) {
-#if defined(AUDIO_USE_C_IMPLEMENTATION_DEFINED_BEHAVIOR) && defined(__GNUC__)
- *d++ = (s[0] >> 1) + (s[1] >> 1);
-#else
- *d++ = (s[0] / 2) + (s[1] / 2);
-#endif
+ *d++ = AUDIO_SCALEDOWN(s[0], 1) + AUDIO_SCALEDOWN(s[1], 1);
s += arg->srcfmt->channels;
}
}
@@ -5021,11 +5035,7 @@ audio_pmixer_process(struct audio_softc *sc)
if (vol != 256) {
m = mixer->mixsample;
for (i = 0; i < sample_count; i++) {
-#if defined(AUDIO_USE_C_IMPLEMENTATION_DEFINED_BEHAVIOR) && defined(__GNUC__)
- *m = *m * vol >> 8;
-#else
- *m = *m * vol / 256;
-#endif
+ *m = AUDIO_SCALEDOWN(*m * vol, 8);
m++;
}
}
@@ -5113,11 +5123,9 @@ audio_pmixer_mix_track(audio_trackmixer_t *mixer,
audio_track_t *track,
#if defined(AUDIO_SUPPORT_TRACK_VOLUME)
if (track->volume != 256) {
for (i = 0; i < sample_count; i++) {
-#if defined(AUDIO_USE_C_IMPLEMENTATION_DEFINED_BEHAVIOR) && defined(__GNUC__)
- *d++ = ((aint2_t)*s++) * track->volume >> 8;
-#else
- *d++ = ((aint2_t)*s++) * track->volume / 256;
-#endif
+ aint2_t v;
+ v = *s++;
+ *d++ = AUDIO_SCALEDOWN(v * track->volume, 8)
}
} else
#endif
@@ -5131,11 +5139,9 @@ audio_pmixer_mix_track(audio_trackmixer_t *mixer,
audio_track_t *track,
#if defined(AUDIO_SUPPORT_TRACK_VOLUME)
if (track->volume != 256) {
for (i = 0; i < sample_count; i++) {
-#if defined(AUDIO_USE_C_IMPLEMENTATION_DEFINED_BEHAVIOR) && defined(__GNUC__)
- *d++ += ((aint2_t)*s++) * track->volume >> 8;
-#else
- *d++ += ((aint2_t)*s++) * track->volume / 256;
-#endif
+ aint2_t v;
+ v = *s++;
+ *d++ += AUDIO_SCALEDOWN(v * track->volume, 8);
}
} else
#endif
--- sys/dev/audio/audiodef.h
+++ sys/dev/audio/audiodef.h
@@ -63,12 +63,6 @@
*/
/* #define AUDIO_SUPPORT_TRACK_VOLUME */
-/*
- * Whether use C language's "implementation defined" behavior (note that
- * it's not "undefined" behavior). It improves performance well.
- */
-#define AUDIO_USE_C_IMPLEMENTATION_DEFINED_BEHAVIOR
-
/* conversion stage */
typedef struct {
audio_ring_t srcbuf;
---
Tetsuya Isaki <is...@pastel-flower.jp / is...@netbsd.org>
