linux / linux / kernel / git / torvalds / linux / a21b0696261c2865d329afa4156ce15fcdf5e772 / . / arch / alpha / lib / memchr.S

/* Copyright (C) 1996 Free Software Foundation, Inc. | |

This file is part of the GNU C Library. | |

Contributed by David Mosberger (davidm@cs.arizona.edu). | |

The GNU C Library is free software; you can redistribute it and/or | |

modify it under the terms of the GNU Library General Public License as | |

published by the Free Software Foundation; either version 2 of the | |

License, or (at your option) any later version. | |

The GNU C Library 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 | |

Library General Public License for more details. | |

You should have received a copy of the GNU Library General Public | |

License along with the GNU C Library; see the file COPYING.LIB. If not, | |

write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, | |

Boston, MA 02111-1307, USA. */ | |

/* Finds characters in a memory area. Optimized for the Alpha: | |

- memory accessed as aligned quadwords only | |

- uses cmpbge to compare 8 bytes in parallel | |

- does binary search to find 0 byte in last | |

quadword (HAKMEM needed 12 instructions to | |

do this instead of the 9 instructions that | |

binary search needs). | |

For correctness consider that: | |

- only minimum number of quadwords may be accessed | |

- the third argument is an unsigned long | |

*/ | |

.set noreorder | |

.set noat | |

.globl memchr | |

.ent memchr | |

memchr: | |

.frame $30,0,$26,0 | |

.prologue 0 | |

# Hack -- if someone passes in (size_t)-1, hoping to just | |

# search til the end of the address space, we will overflow | |

# below when we find the address of the last byte. Given | |

# that we will never have a 56-bit address space, cropping | |

# the length is the easiest way to avoid trouble. | |

zap $18, 0x80, $5 #-e0 : | |

beq $18, $not_found # .. e1 : | |

ldq_u $1, 0($16) # e1 : load first quadword | |

insbl $17, 1, $2 # .. e0 : $2 = 000000000000ch00 | |

and $17, 0xff, $17 #-e0 : $17 = 00000000000000ch | |

cmpult $18, 9, $4 # .. e1 : | |

or $2, $17, $17 # e0 : $17 = 000000000000chch | |

lda $3, -1($31) # .. e1 : | |

sll $17, 16, $2 #-e0 : $2 = 00000000chch0000 | |

addq $16, $5, $5 # .. e1 : | |

or $2, $17, $17 # e1 : $17 = 00000000chchchch | |

unop # : | |

sll $17, 32, $2 #-e0 : $2 = chchchch00000000 | |

or $2, $17, $17 # e1 : $17 = chchchchchchchch | |

extql $1, $16, $7 # e0 : | |

beq $4, $first_quad # .. e1 : | |

ldq_u $6, -1($5) #-e1 : eight or less bytes to search | |

extqh $6, $16, $6 # .. e0 : | |

mov $16, $0 # e0 : | |

or $7, $6, $1 # .. e1 : $1 = quadword starting at $16 | |

# Deal with the case where at most 8 bytes remain to be searched | |

# in $1. E.g.: | |

# $18 = 6 | |

# $1 = ????c6c5c4c3c2c1 | |

$last_quad: | |

negq $18, $6 #-e0 : | |

xor $17, $1, $1 # .. e1 : | |

srl $3, $6, $6 # e0 : $6 = mask of $18 bits set | |

cmpbge $31, $1, $2 # .. e1 : | |

and $2, $6, $2 #-e0 : | |

beq $2, $not_found # .. e1 : | |

$found_it: | |

# Now, determine which byte matched: | |

negq $2, $3 # e0 : | |

and $2, $3, $2 # e1 : | |

and $2, 0x0f, $1 #-e0 : | |

addq $0, 4, $3 # .. e1 : | |

cmoveq $1, $3, $0 # e0 : | |

addq $0, 2, $3 # .. e1 : | |

and $2, 0x33, $1 #-e0 : | |

cmoveq $1, $3, $0 # .. e1 : | |

and $2, 0x55, $1 # e0 : | |

addq $0, 1, $3 # .. e1 : | |

cmoveq $1, $3, $0 #-e0 : | |

$done: ret # .. e1 : | |

# Deal with the case where $18 > 8 bytes remain to be | |

# searched. $16 may not be aligned. | |

.align 4 | |

$first_quad: | |

andnot $16, 0x7, $0 #-e1 : | |

insqh $3, $16, $2 # .. e0 : $2 = 0000ffffffffffff ($16<0:2> ff) | |

xor $1, $17, $1 # e0 : | |

or $1, $2, $1 # e1 : $1 = ====ffffffffffff | |

cmpbge $31, $1, $2 #-e0 : | |

bne $2, $found_it # .. e1 : | |

# At least one byte left to process. | |

ldq $1, 8($0) # e0 : | |

subq $5, 1, $18 # .. e1 : | |

addq $0, 8, $0 #-e0 : | |

# Make $18 point to last quad to be accessed (the | |

# last quad may or may not be partial). | |

andnot $18, 0x7, $18 # .. e1 : | |

cmpult $0, $18, $2 # e0 : | |

beq $2, $final # .. e1 : | |

# At least two quads remain to be accessed. | |

subq $18, $0, $4 #-e0 : $4 <- nr quads to be processed | |

and $4, 8, $4 # e1 : odd number of quads? | |

bne $4, $odd_quad_count # e1 : | |

# At least three quads remain to be accessed | |

mov $1, $4 # e0 : move prefetched value to correct reg | |

.align 4 | |

$unrolled_loop: | |

ldq $1, 8($0) #-e0 : prefetch $1 | |

xor $17, $4, $2 # .. e1 : | |

cmpbge $31, $2, $2 # e0 : | |

bne $2, $found_it # .. e1 : | |

addq $0, 8, $0 #-e0 : | |

$odd_quad_count: | |

xor $17, $1, $2 # .. e1 : | |

ldq $4, 8($0) # e0 : prefetch $4 | |

cmpbge $31, $2, $2 # .. e1 : | |

addq $0, 8, $6 #-e0 : | |

bne $2, $found_it # .. e1 : | |

cmpult $6, $18, $6 # e0 : | |

addq $0, 8, $0 # .. e1 : | |

bne $6, $unrolled_loop #-e1 : | |

mov $4, $1 # e0 : move prefetched value into $1 | |

$final: subq $5, $0, $18 # .. e1 : $18 <- number of bytes left to do | |

bne $18, $last_quad # e1 : | |

$not_found: | |

mov $31, $0 #-e0 : | |

ret # .. e1 : | |

.end memchr |