cosmopolitan/libc/nexgen32e/llog10.S

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/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8 -*-│
vi: set et ft=asm ts=8 sw=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"
/ Fast log when 𝑥 is an integer.
/
/ @param rdi is uint64 𝑥
/ @domain 0<𝑥<2⁶⁴ ∧ 𝑥∊ℤ
llog10: .leafprologue
.profilable
bsr %rdi,%rax
jz 3f
lea llog10data(%rip),%rdx
movsbl 1(%rdx,%rax),%eax
cmp 2f-1f(%rdx,%rax,8),%rdi
sbb $0,%al
jmp 4f
3: xor %eax,%eax # domain error
4: .leafepilogue
.endfn llog10,globl
.rodata
llog10data:
1: .byte 0, 0, 0, 0, 1, 1, 1, 2, 2, 2, 3, 3, 3, 3, 4, 4
.byte 4, 5, 5, 5, 6, 6, 6, 6, 7, 7, 7, 8, 8, 8, 9, 9
.byte 9, 9,10,10,10,11,11,11,12,12,12,12,13,13,13,14
.byte 14,14,15,15,15,15,16,16,16,17,17,17,18,18,18,18
.byte 19,19,19
.align 8
2: .quad 0
.quad 10
.quad 100
.quad 1000
.quad 10000
.quad 100000
.quad 1000000
.quad 10000000
.quad 100000000
.quad 1000000000
.quad 10000000000
.quad 100000000000
.quad 1000000000000
.quad 10000000000000
.quad 100000000000000
.quad 1000000000000000
.quad 10000000000000000
.quad 100000000000000000
.endobj llog10data
.previous
.source __FILE__