1/* Copyright (C) 1996 Free Software Foundation, Inc. 2 This file is part of the GNU C Library. 3 Contributed by David Mosberger (davidm@cs.arizona.edu). 4 5 The GNU C Library is free software; you can redistribute it and/or 6 modify it under the terms of the GNU Library General Public License as 7 published by the Free Software Foundation; either version 2 of the 8 License, or (at your option) any later version. 9 10 The GNU C Library is distributed in the hope that it will be useful, 11 but WITHOUT ANY WARRANTY; without even the implied warranty of 12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 13 Library General Public License for more details. 14 15 You should have received a copy of the GNU Library General Public 16 License along with the GNU C Library; see the file COPYING.LIB. If not, 17 write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, 18 Boston, MA 02111-1307, USA. */ 19 20/* Finds characters in a memory area. Optimized for the Alpha: 21 22 - memory accessed as aligned quadwords only 23 - uses cmpbge to compare 8 bytes in parallel 24 - does binary search to find 0 byte in last 25 quadword (HAKMEM needed 12 instructions to 26 do this instead of the 9 instructions that 27 binary search needs). 28 29For correctness consider that: 30 31 - only minimum number of quadwords may be accessed 32 - the third argument is an unsigned long 33*/ 34 35 .set noreorder 36 .set noat 37 38 .globl memchr 39 .ent memchr 40memchr: 41 .frame $30,0,$26,0 42 .prologue 0 43 44 # Hack -- if someone passes in (size_t)-1, hoping to just 45 # search til the end of the address space, we will overflow 46 # below when we find the address of the last byte. Given 47 # that we will never have a 56-bit address space, cropping 48 # the length is the easiest way to avoid trouble. 49 zap $18, 0x80, $5 #-e0 : 50 51 beq $18, $not_found # .. e1 : 52 ldq_u $1, 0($16) # e1 : load first quadword 53 insbl $17, 1, $2 # .. e0 : $2 = 000000000000ch00 54 and $17, 0xff, $17 #-e0 : $17 = 00000000000000ch 55 cmpult $18, 9, $4 # .. e1 : 56 or $2, $17, $17 # e0 : $17 = 000000000000chch 57 lda $3, -1($31) # .. e1 : 58 sll $17, 16, $2 #-e0 : $2 = 00000000chch0000 59 addq $16, $5, $5 # .. e1 : 60 or $2, $17, $17 # e1 : $17 = 00000000chchchch 61 unop # : 62 sll $17, 32, $2 #-e0 : $2 = chchchch00000000 63 or $2, $17, $17 # e1 : $17 = chchchchchchchch 64 extql $1, $16, $7 # e0 : 65 beq $4, $first_quad # .. e1 : 66 67 ldq_u $6, -1($5) #-e1 : eight or less bytes to search 68 extqh $6, $16, $6 # .. e0 : 69 mov $16, $0 # e0 : 70 or $7, $6, $1 # .. e1 : $1 = quadword starting at $16 71 72 # Deal with the case where at most 8 bytes remain to be searched 73 # in $1. E.g.: 74 # $18 = 6 75 # $1 = ????c6c5c4c3c2c1 76$last_quad: 77 negq $18, $6 #-e0 : 78 xor $17, $1, $1 # .. e1 : 79 srl $3, $6, $6 # e0 : $6 = mask of $18 bits set 80 cmpbge $31, $1, $2 # .. e1 : 81 and $2, $6, $2 #-e0 : 82 beq $2, $not_found # .. e1 : 83 84$found_it: 85 # Now, determine which byte matched: 86 negq $2, $3 # e0 : 87 and $2, $3, $2 # e1 : 88 89 and $2, 0x0f, $1 #-e0 : 90 addq $0, 4, $3 # .. e1 : 91 cmoveq $1, $3, $0 # e0 : 92 93 addq $0, 2, $3 # .. e1 : 94 and $2, 0x33, $1 #-e0 : 95 cmoveq $1, $3, $0 # .. e1 : 96 97 and $2, 0x55, $1 # e0 : 98 addq $0, 1, $3 # .. e1 : 99 cmoveq $1, $3, $0 #-e0 : 100 101$done: ret # .. e1 : 102 103 # Deal with the case where $18 > 8 bytes remain to be 104 # searched. $16 may not be aligned. 105 .align 4 106$first_quad: 107 andnot $16, 0x7, $0 #-e1 : 108 insqh $3, $16, $2 # .. e0 : $2 = 0000ffffffffffff ($16<0:2> ff) 109 xor $1, $17, $1 # e0 : 110 or $1, $2, $1 # e1 : $1 = ====ffffffffffff 111 cmpbge $31, $1, $2 #-e0 : 112 bne $2, $found_it # .. e1 : 113 114 # At least one byte left to process. 115 116 ldq $1, 8($0) # e0 : 117 subq $5, 1, $18 # .. e1 : 118 addq $0, 8, $0 #-e0 : 119 120 # Make $18 point to last quad to be accessed (the 121 # last quad may or may not be partial). 122 123 andnot $18, 0x7, $18 # .. e1 : 124 cmpult $0, $18, $2 # e0 : 125 beq $2, $final # .. e1 : 126 127 # At least two quads remain to be accessed. 128 129 subq $18, $0, $4 #-e0 : $4 <- nr quads to be processed 130 and $4, 8, $4 # e1 : odd number of quads? 131 bne $4, $odd_quad_count # e1 : 132 133 # At least three quads remain to be accessed 134 135 mov $1, $4 # e0 : move prefetched value to correct reg 136 137 .align 4 138$unrolled_loop: 139 ldq $1, 8($0) #-e0 : prefetch $1 140 xor $17, $4, $2 # .. e1 : 141 cmpbge $31, $2, $2 # e0 : 142 bne $2, $found_it # .. e1 : 143 144 addq $0, 8, $0 #-e0 : 145$odd_quad_count: 146 xor $17, $1, $2 # .. e1 : 147 ldq $4, 8($0) # e0 : prefetch $4 148 cmpbge $31, $2, $2 # .. e1 : 149 addq $0, 8, $6 #-e0 : 150 bne $2, $found_it # .. e1 : 151 152 cmpult $6, $18, $6 # e0 : 153 addq $0, 8, $0 # .. e1 : 154 bne $6, $unrolled_loop #-e1 : 155 156 mov $4, $1 # e0 : move prefetched value into $1 157$final: subq $5, $0, $18 # .. e1 : $18 <- number of bytes left to do 158 bne $18, $last_quad # e1 : 159 160$not_found: 161 mov $31, $0 #-e0 : 162 ret # .. e1 : 163 164 .end memchr 165