cosmopolitan/dsp/core/mulaw.S

64 lines
2.8 KiB
ArmAsm

/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8 -*-│
vi: set et ft=asm ts=8 tw=8 fenc=utf-8 :vi
Copyright 2020 Justine Alexandra Roberts Tunney
Permission to use, copy, modify, and/or distribute this software for
any purpose with or without fee is hereby granted, provided that the
above copyright notice and this permission notice appear in all copies.
THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
PERFORMANCE OF THIS SOFTWARE.
*/
#include "libc/macros.h"
#define BIAS 0x84
/ Encodes audio sample with µ-Law.
/
/ This is both the highest quality and most widely supported
/ telephony codec, whose use was phased out in the 2000's in
/ favor of cost-saving GSM audio compression that was so bad
/ consumers were willing to pay more cash, for the privilege
/ of saving telcos even more money w/ text messaging. Mu Law
/ reduces PCM data to half its original size, by diminishing
/ audio bands not vocalized by human voice.
/
/ @param %edi is pcm sample
/ @return %eax is uint8_t encoded sample
mulaw: .leafprologue
.profilable
mov $BIAS,%eax
xor %edx,%edx
test %edi,%edi
js 1f
lea (%edi,%eax),%eax
mov $0xFF,%dl
jmp 2f
1: sub %edi,%eax
mov $0x7F,%dl
2: mov %eax,%esi
or $0xFF,%sil
bsr %esi,%esi
sub $7,%esi
cmp $8,%esi
jge 4f
lea 3(%rdx),%ecx
sar %cl,%eax
and $0xF,%eax
shl $4,%esi
or %esi,%eax
xor %edx,%eax
3: .leafepilogue
4: xor $0x7F,%dl
mov %edx,%eax
jmp 3b
.endfn mulaw,globl
.source __FILE__