mirror of
https://github.com/jart/cosmopolitan.git
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8bfd56b59e
Now that these functions are behind _COSMO_SOURCE there's no reason for having the ugly underscore anymore. To use these functions, you need to pass -mcosmo to cosmocc.
72 lines
3.7 KiB
C
72 lines
3.7 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│ vi: set et ft=c ts=2 sts=2 sw=2 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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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/intrin/bsf.h"
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/**
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* Returns position of first bit set.
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*
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* ctz(𝑥) 31^clz(𝑥) clz(𝑥)
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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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* @param 𝑥 is a 64-bit integer
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* @return number in range 0..63 or undefined if 𝑥 is 0
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*/
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int(bsfl)(long x) {
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unsigned l, r;
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x &= -x;
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l = x | x >> 32;
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r = !!(x >> 32), r <<= 1;
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r += !!((l & 0xffff0000)), r <<= 1;
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r += !!((l & 0xff00ff00)), r <<= 1;
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r += !!((l & 0xf0f0f0f0)), r <<= 1;
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r += !!((l & 0xcccccccc)), r <<= 1;
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r += !!((l & 0xaaaaaaaa));
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return r;
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}
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/**
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* Returns position of first bit set.
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*
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* ctz(𝑥) 31^clz(𝑥) clz(𝑥)
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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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* @param x is a 32-bit integer
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* @return number in range 0..31 or undefined if 𝑥 is 0
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*/
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int(bsf)(int x) {
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return bsf((unsigned)x);
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}
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__weak_reference(bsfl, bsfll);
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