Module Name: src
Committed By: isaki
Date: Sat Sep 12 06:09:17 UTC 2020
Modified Files:
src/sys/dev/audio: mulaw.c
Log Message:
Improve slinear16-to-mulaw conversion calculation.
It's about 2~3 times faster on my amd64 and x68k(68030).
To generate a diff of this commit:
cvs rdiff -u -r1.3 -r1.4 src/sys/dev/audio/mulaw.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/dev/audio/mulaw.c
diff -u src/sys/dev/audio/mulaw.c:1.3 src/sys/dev/audio/mulaw.c:1.4
--- src/sys/dev/audio/mulaw.c:1.3 Sat Jan 11 04:06:13 2020
+++ src/sys/dev/audio/mulaw.c Sat Sep 12 06:09:16 2020
@@ -1,4 +1,4 @@
-/* $NetBSD: mulaw.c,v 1.3 2020/01/11 04:06:13 isaki Exp $ */
+/* $NetBSD: mulaw.c,v 1.4 2020/09/12 06:09:16 isaki Exp $ */
/*
* Copyright (C) 2017 Tetsuya Isaki. All rights reserved.
@@ -27,7 +27,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: mulaw.c,v 1.3 2020/01/11 04:06:13 isaki Exp $");
+__KERNEL_RCSID(0, "$NetBSD: mulaw.c,v 1.4 2020/09/12 06:09:16 isaki Exp $");
#include <sys/types.h>
#include <sys/systm.h>
@@ -45,7 +45,7 @@ __KERNEL_RCSID(0, "$NetBSD: mulaw.c,v 1.
*
* 2. Calculation (default)
* It calculates mu-law with full spec and its precision is 14bit.
- * It's about 10 times slower but the size is less than a half (on m68k,
+ * It's about 3 times slower but the size is less than a half (on m68k,
* for example).
*
* mu-law is no longer a popular format. I think size-optimized is better.
@@ -247,33 +247,40 @@ audio_internal_to_mulaw32(audio_filter_a
m = slinear8_to_mulaw[val];
#else
/* 14bit (fullspec, slow but small) encoder */
- int16_t val;
+ uint16_t val;
int c;
- val = (int16_t)(*s++ >> (AUDIO_INTERNAL_BITS - 16));
- if (val < 0) {
+ val = *s++ >> (AUDIO_INTERNAL_BITS - 16);
+ if ((int16_t)val < 0) {
m = 0;
} else {
val = ~val;
m = 0x80;
}
/* limit */
- if (val < -8158 * 4)
+ if ((int16_t)val < -8158 * 4)
val = -8158 * 4;
val -= 33 * 4; /* bias */
- val <<= 1;
- for (c = 0; c < 7; c++) {
- if (val >= 0) {
- break;
- }
+ // Before(1) Before(2) Before(3)
+ // S0MMMMxx_xxxxxxxx 0MMMMxxx_xxxxxxx0 c=0,v=0MMMMxxx_xxxxxxx0
+ // S10MMMMx_xxxxxxxx 10MMMMxx_xxxxxxx0 c=1,v=0MMMMxxx_xxxxxx00
+ // S110MMMM_xxxxxxxx 110MMMMx_xxxxxxx0 c=2,v=0MMMMxxx_xxxxx000
+ // : : :
+ // S1111110_MMMMxxxx 1111110M_MMMxxxx0 c=6,v=0MMMMxxx_x0000000
- m += (1 << 4); /* exponent */
- val <<= 1;
- }
+ // (1) Push out sign bit
val <<= 1;
- m += (val >> 12) & 0x0f; /* mantissa */
+ // (2) Find first zero (and align val to left)
+ c = 0;
+ if (val >= 0xf000) c += 4, val <<= 4;
+ if (val >= 0xc000) c += 2, val <<= 2;
+ if (val >= 0x8000) c += 1, val <<= 1;
+
+ // (3)
+ m += (c << 4);
+ m += (val >> 11) & 0x0f;
#endif
#if defined(MULAW32)
