/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8     -*-â
âvi: set et ft=asm ts=8 tw=8 fenc=utf-8                                     :viâ
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â Copyright 2020 Justine Alexandra Roberts Tunney                              â
â                                                                              â
â Permission to use, copy, modify, and/or distribute this software for         â
â any purpose with or without fee is hereby granted, provided that the         â
â above copyright notice and this permission notice appear in all copies.      â
â                                                                              â
â THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                â
â WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                â
â WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             â
â AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         â
â DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        â
â PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               â
â TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             â
â PERFORMANCE OF THIS SOFTWARE.                                                â
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#include "libc/macros.internal.h"

//	Returns binary logarithm of integer ð¥.
//
//	      uint32 ð¥  _bsf(ð¥) tzcnt(ð¥)   ffs(ð¥)   bsr(ð¥) lzcnt(ð¥)
//	    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
//
//	@param	rsi:rdi is 128-bit unsigned ð¥ value
//	@return	eax number in range [0,128) or undef if ð¥ is 0
//	@see	also treasure trove of nearly identical functions
_bsr128:
	.leafprologue
	.profilable
	bsr	%rsi,%rax
	jnz	2f
	bsr	%rdi,%rax
1:	.leafepilogue
2:	add	$64,%eax
	jmp	1b
	.endfn	_bsr128,globl
