cosmopolitan/libc/str/tpenc.S

72 lines
2.8 KiB
ArmAsm

/*-*- 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__
/ Encodes Thompson-Pike varint.
/
/ @param edi is int to encode
/ @return rax is word-encoded byte buffer
/ @clob edi,rax,flags
/ @note invented on a napkin in a new jersey diner
tpenc: .leafprologue
.profilable
push %rcx
push %rdx
mov %edi,%edi
xor %eax,%eax
cmp $127,%edi
jbe 3f
bsr %edi,%ecx
ezlea kTpenc,dx
mov -7*(1+1)(%rdx,%rcx,2),%ecx
1: mov %edi,%edx
shr $6,%edi
and $0b00111111,%dl
or $0b10000000,%al
or %dl,%al
shl $8,%rax
dec %cl
jnz 1b
2: or %ch,%al
3: or %rdi,%rax
pop %rdx
pop %rcx
.leafepilogue
.endfn tpenc,globl
.rodata
kTpenc: .rept 4 # MSB10 (0x7FF)
.byte 1,0b11000000 # len,mark
.endr
.rept 5 # MSB15 (0xFFFF)
.byte 2,0b11100000 # len,mark
.endr
.rept 5 # MSB20 (0x1FFFFF)
.byte 3,0b11110000 # len,mark
.endr
.rept 5 # MSB25 (0x3FFFFFF)
.byte 4,0b11111000 # len,mark
.endr
.rept 6 # MSB31 (0xffffffff)
.byte 5,0b11111100 # len,mark
.endr
.endobj kTpenc