65 lines
2.8 KiB
ArmAsm
65 lines
2.8 KiB
ArmAsm
/*-*- mode:asm; indent-tabs-mode:t; tab-width:8; coding:utf-8 -*-│
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│vi: set et ft=asm ts=8 tw=8 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2020 Justine Alexandra Roberts Tunney │
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│ │
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│ This program is free software; you can redistribute it and/or modify │
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│ it under the terms of the GNU General Public License as published by │
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│ the Free Software Foundation; version 2 of the License. │
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│ │
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│ This program is distributed in the hope that it will be useful, but │
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│ WITHOUT ANY WARRANTY; without even the implied warranty of │
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│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
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│ General Public License for more details. │
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│ │
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│ You should have received a copy of the GNU General Public License │
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│ along with this program; if not, write to the Free Software │
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│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
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│ 02110-1301 USA │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/macros.h"
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#define BIAS 0x84
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/ Encodes audio sample with µ-Law.
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/
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/ This is both the highest quality and most widely supported
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/ telephony codec, whose use was phased out in the 2000's in
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/ favor of cost-saving GSM audio compression that was so bad
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/ consumers were willing to pay more cash, for the privilege
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/ of saving telcos even more money w/ text messaging. Mu Law
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/ reduces PCM data to half its original size, by diminishing
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/ audio bands not vocalized by human voice.
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/
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/ @param %edi is pcm sample
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/ @return %eax is uint8_t encoded sample
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mulaw: .leafprologue
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.profilable
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mov $BIAS,%eax
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xor %edx,%edx
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test %edi,%edi
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js 1f
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lea (%edi,%eax),%eax
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mov $0xFF,%dl
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jmp 2f
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1: sub %edi,%eax
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mov $0x7F,%dl
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2: mov %eax,%esi
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or $0xFF,%sil
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bsr %esi,%esi
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sub $7,%esi
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cmp $8,%esi
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jge 4f
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lea 3(%rdx),%ecx
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sar %cl,%eax
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and $0xF,%eax
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shl $4,%esi
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or %esi,%eax
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xor %edx,%eax
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3: .leafepilogue
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4: xor $0x7F,%dl
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mov %edx,%eax
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jmp 3b
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.endfn mulaw,globl
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.source __FILE__
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