cosmopolitan/libc/nexgen32e/tzcnt.S

46 lines
2.8 KiB
ArmAsm
Raw Blame History

This file contains ambiguous Unicode characters!

This file contains ambiguous Unicode characters that may be confused with others in your current locale. If your use case is intentional and legitimate, you can safely ignore this warning. Use the Escape button to highlight these characters.

/*-*- 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
This program is free software; you can redistribute it and/or modify │
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License. │
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of │
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software │
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA
*/
#include "libc/macros.h"
.source __FILE__
/ Finds lowest set bit in 𝑥.
/
/ @param edi is 32-bit unsigned 𝑥 value
/ @return eax number in range [0,32) or 32 if 𝑥 is 0
/ @see also treasure trove of nearly identical functions
/
/ uint32 𝑥 bsf(𝑥) tzcnt(𝑥) ffs(𝑥) bsr(𝑥) lzcnt(𝑥)
/ 0x00000000 wut 32 0 wut 32
/ 0x00000001 0 0 1 0 31
/ 0x80000001 0 0 1 31 0
/ 0x80000000 31 31 32 31 0
/ 0x00000010 4 4 5 4 27
/ 0x08000010 4 4 5 27 4
/ 0x08000000 27 27 28 27 4
/ 0xffffffff 0 0 1 31 0
/
tzcnt: .leafprologue
.profilable
mov $32,%esi
bsf %edi,%eax
cmovz %esi,%eax
.leafepilogue
.endfn tzcnt,globl