2020-06-16 13:38:43 +00:00
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/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8 -*-│
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2020-06-15 14:18:57 +00:00
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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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/ Finds leading bits in 𝑥.
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/
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/ @param edi is 32-bit unsigned 𝑥 value
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/ @return eax number in range [0,32) or 32 if 𝑥 is 0
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/ @see also treasure trove of nearly identical functions
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/
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/ uint32 𝑥 bsf(𝑥) tzcnt(𝑥) ffs(𝑥) bsr(𝑥) lzcnt(𝑥)
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/ 0x00000000 wut 32 0 wut 32
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/ 0x00000001 0 0 1 0 31
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/ 0x80000001 0 0 1 31 0
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/ 0x80000000 31 31 32 31 0
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/ 0x00000010 4 4 5 4 27
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/ 0x08000010 4 4 5 27 4
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/ 0x08000000 27 27 28 27 4
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/ 0xffffffff 0 0 1 31 0
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/
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lzcnt: .leafprologue
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.profilable
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mov $31,%eax
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mov $-1,%edx
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bsr %edi,%ecx
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cmovz %edx,%ecx
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sub %ecx,%eax
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.leafepilogue
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.endfn lzcnt,globl
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2020-06-16 02:01:28 +00:00
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.source __FILE__
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