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165 lines
4.9 KiB
165 lines
4.9 KiB
/* Copyright (C) 1996 Free Software Foundation, Inc. |
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This file is part of the GNU C Library. |
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Contributed by David Mosberger (davidm@cs.arizona.edu). |
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The GNU C Library is free software; you can redistribute it and/or |
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modify it under the terms of the GNU Library General Public License as |
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published by the Free Software Foundation; either version 2 of the |
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License, or (at your option) any later version. |
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The GNU C Library is distributed in the hope that it will be useful, |
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but WITHOUT ANY WARRANTY; without even the implied warranty of |
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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Library General Public License for more details. |
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You should have received a copy of the GNU Library General Public |
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License along with the GNU C Library; see the file COPYING.LIB. If not, |
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write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, |
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Boston, MA 02111-1307, USA. */ |
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/* Finds characters in a memory area. Optimized for the Alpha: |
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- memory accessed as aligned quadwords only |
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- uses cmpbge to compare 8 bytes in parallel |
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- does binary search to find 0 byte in last |
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quadword (HAKMEM needed 12 instructions to |
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do this instead of the 9 instructions that |
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binary search needs). |
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For correctness consider that: |
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- only minimum number of quadwords may be accessed |
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- the third argument is an unsigned long |
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*/ |
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#include <asm/export.h> |
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.set noreorder |
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.set noat |
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.globl memchr |
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.ent memchr |
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memchr: |
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.frame $30,0,$26,0 |
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.prologue 0 |
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# Hack -- if someone passes in (size_t)-1, hoping to just |
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# search til the end of the address space, we will overflow |
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# below when we find the address of the last byte. Given |
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# that we will never have a 56-bit address space, cropping |
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# the length is the easiest way to avoid trouble. |
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zap $18, 0x80, $5 #-e0 : |
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beq $18, $not_found # .. e1 : |
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ldq_u $1, 0($16) # e1 : load first quadword |
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insbl $17, 1, $2 # .. e0 : $2 = 000000000000ch00 |
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and $17, 0xff, $17 #-e0 : $17 = 00000000000000ch |
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cmpult $18, 9, $4 # .. e1 : |
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or $2, $17, $17 # e0 : $17 = 000000000000chch |
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lda $3, -1($31) # .. e1 : |
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sll $17, 16, $2 #-e0 : $2 = 00000000chch0000 |
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addq $16, $5, $5 # .. e1 : |
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or $2, $17, $17 # e1 : $17 = 00000000chchchch |
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unop # : |
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sll $17, 32, $2 #-e0 : $2 = chchchch00000000 |
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or $2, $17, $17 # e1 : $17 = chchchchchchchch |
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extql $1, $16, $7 # e0 : |
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beq $4, $first_quad # .. e1 : |
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ldq_u $6, -1($5) #-e1 : eight or less bytes to search |
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extqh $6, $16, $6 # .. e0 : |
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mov $16, $0 # e0 : |
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or $7, $6, $1 # .. e1 : $1 = quadword starting at $16 |
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# Deal with the case where at most 8 bytes remain to be searched |
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# in $1. E.g.: |
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# $18 = 6 |
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# $1 = ????c6c5c4c3c2c1 |
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$last_quad: |
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negq $18, $6 #-e0 : |
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xor $17, $1, $1 # .. e1 : |
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srl $3, $6, $6 # e0 : $6 = mask of $18 bits set |
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cmpbge $31, $1, $2 # .. e1 : |
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and $2, $6, $2 #-e0 : |
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beq $2, $not_found # .. e1 : |
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$found_it: |
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# Now, determine which byte matched: |
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negq $2, $3 # e0 : |
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and $2, $3, $2 # e1 : |
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and $2, 0x0f, $1 #-e0 : |
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addq $0, 4, $3 # .. e1 : |
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cmoveq $1, $3, $0 # e0 : |
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addq $0, 2, $3 # .. e1 : |
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and $2, 0x33, $1 #-e0 : |
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cmoveq $1, $3, $0 # .. e1 : |
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and $2, 0x55, $1 # e0 : |
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addq $0, 1, $3 # .. e1 : |
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cmoveq $1, $3, $0 #-e0 : |
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$done: ret # .. e1 : |
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# Deal with the case where $18 > 8 bytes remain to be |
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# searched. $16 may not be aligned. |
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.align 4 |
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$first_quad: |
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andnot $16, 0x7, $0 #-e1 : |
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insqh $3, $16, $2 # .. e0 : $2 = 0000ffffffffffff ($16<0:2> ff) |
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xor $1, $17, $1 # e0 : |
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or $1, $2, $1 # e1 : $1 = ====ffffffffffff |
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cmpbge $31, $1, $2 #-e0 : |
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bne $2, $found_it # .. e1 : |
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# At least one byte left to process. |
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ldq $1, 8($0) # e0 : |
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subq $5, 1, $18 # .. e1 : |
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addq $0, 8, $0 #-e0 : |
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# Make $18 point to last quad to be accessed (the |
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# last quad may or may not be partial). |
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andnot $18, 0x7, $18 # .. e1 : |
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cmpult $0, $18, $2 # e0 : |
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beq $2, $final # .. e1 : |
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# At least two quads remain to be accessed. |
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subq $18, $0, $4 #-e0 : $4 <- nr quads to be processed |
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and $4, 8, $4 # e1 : odd number of quads? |
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bne $4, $odd_quad_count # e1 : |
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# At least three quads remain to be accessed |
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mov $1, $4 # e0 : move prefetched value to correct reg |
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.align 4 |
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$unrolled_loop: |
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ldq $1, 8($0) #-e0 : prefetch $1 |
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xor $17, $4, $2 # .. e1 : |
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cmpbge $31, $2, $2 # e0 : |
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bne $2, $found_it # .. e1 : |
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addq $0, 8, $0 #-e0 : |
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$odd_quad_count: |
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xor $17, $1, $2 # .. e1 : |
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ldq $4, 8($0) # e0 : prefetch $4 |
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cmpbge $31, $2, $2 # .. e1 : |
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addq $0, 8, $6 #-e0 : |
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bne $2, $found_it # .. e1 : |
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cmpult $6, $18, $6 # e0 : |
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addq $0, 8, $0 # .. e1 : |
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bne $6, $unrolled_loop #-e1 : |
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mov $4, $1 # e0 : move prefetched value into $1 |
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$final: subq $5, $0, $18 # .. e1 : $18 <- number of bytes left to do |
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bne $18, $last_quad # e1 : |
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$not_found: |
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mov $31, $0 #-e0 : |
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ret # .. e1 : |
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.end memchr |
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EXPORT_SYMBOL(memchr)
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