1/* 2 * arch/alpha/lib/ev6-memchr.S 3 * 4 * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com> 5 * 6 * Finds characters in a memory area. Optimized for the Alpha: 7 * 8 * - memory accessed as aligned quadwords only 9 * - uses cmpbge to compare 8 bytes in parallel 10 * - does binary search to find 0 byte in last 11 * quadword (HAKMEM needed 12 instructions to 12 * do this instead of the 9 instructions that 13 * binary search needs). 14 * 15 * For correctness consider that: 16 * 17 * - only minimum number of quadwords may be accessed 18 * - the third argument is an unsigned long 19 * 20 * Much of the information about 21264 scheduling/coding comes from: 21 * Compiler Writer's Guide for the Alpha 21264 22 * abbreviated as 'CWG' in other comments here 23 * ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html 24 * Scheduling notation: 25 * E - either cluster 26 * U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1 27 * L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1 28 * Try not to change the actual algorithm if possible for consistency. 29 */ 30 31 .set noreorder 32 .set noat 33 34 .align 4 35 .globl memchr 36 .ent memchr 37memchr: 38 .frame $30,0,$26,0 39 .prologue 0 40 41 # Hack -- if someone passes in (size_t)-1, hoping to just 42 # search til the end of the address space, we will overflow 43 # below when we find the address of the last byte. Given 44 # that we will never have a 56-bit address space, cropping 45 # the length is the easiest way to avoid trouble. 46 zap $18, 0x80, $5 # U : Bound length 47 beq $18, $not_found # U : 48 ldq_u $1, 0($16) # L : load first quadword Latency=3 49 and $17, 0xff, $17 # E : L L U U : 00000000000000ch 50 51 insbl $17, 1, $2 # U : 000000000000ch00 52 cmpult $18, 9, $4 # E : small (< 1 quad) string? 53 or $2, $17, $17 # E : 000000000000chch 54 lda $3, -1($31) # E : U L L U 55 56 sll $17, 16, $2 # U : 00000000chch0000 57 addq $16, $5, $5 # E : Max search address 58 or $2, $17, $17 # E : 00000000chchchch 59 sll $17, 32, $2 # U : U L L U : chchchch00000000 60 61 or $2, $17, $17 # E : chchchchchchchch 62 extql $1, $16, $7 # U : $7 is upper bits 63 beq $4, $first_quad # U : 64 ldq_u $6, -1($5) # L : L U U L : eight or less bytes to search Latency=3 65 66 extqh $6, $16, $6 # U : 2 cycle stall for $6 67 mov $16, $0 # E : 68 nop # E : 69 or $7, $6, $1 # E : L U L U $1 = quadword starting at $16 70 71 # Deal with the case where at most 8 bytes remain to be searched 72 # in $1. E.g.: 73 # $18 = 6 74 # $1 = ????c6c5c4c3c2c1 75$last_quad: 76 negq $18, $6 # E : 77 xor $17, $1, $1 # E : 78 srl $3, $6, $6 # U : $6 = mask of $18 bits set 79 cmpbge $31, $1, $2 # E : L U L U 80 81 nop 82 nop 83 and $2, $6, $2 # E : 84 beq $2, $not_found # U : U L U L 85 86$found_it: 87#ifdef CONFIG_ALPHA_EV67 88 /* 89 * Since we are guaranteed to have set one of the bits, we don't 90 * have to worry about coming back with a 0x40 out of cttz... 91 */ 92 cttz $2, $3 # U0 : 93 addq $0, $3, $0 # E : All done 94 nop # E : 95 ret # L0 : L U L U 96#else 97 /* 98 * Slow and clunky. It can probably be improved. 99 * An exercise left for others. 100 */ 101 negq $2, $3 # E : 102 and $2, $3, $2 # E : 103 and $2, 0x0f, $1 # E : 104 addq $0, 4, $3 # E : 105 106 cmoveq $1, $3, $0 # E : Latency 2, extra map cycle 107 nop # E : keep with cmov 108 and $2, 0x33, $1 # E : 109 addq $0, 2, $3 # E : U L U L : 2 cycle stall on $0 110 111 cmoveq $1, $3, $0 # E : Latency 2, extra map cycle 112 nop # E : keep with cmov 113 and $2, 0x55, $1 # E : 114 addq $0, 1, $3 # E : U L U L : 2 cycle stall on $0 115 116 cmoveq $1, $3, $0 # E : Latency 2, extra map cycle 117 nop 118 nop 119 ret # L0 : L U L U 120#endif 121 122 # Deal with the case where $18 > 8 bytes remain to be 123 # searched. $16 may not be aligned. 124 .align 4 125$first_quad: 126 andnot $16, 0x7, $0 # E : 127 insqh $3, $16, $2 # U : $2 = 0000ffffffffffff ($16<0:2> ff) 128 xor $1, $17, $1 # E : 129 or $1, $2, $1 # E : U L U L $1 = ====ffffffffffff 130 131 cmpbge $31, $1, $2 # E : 132 bne $2, $found_it # U : 133 # At least one byte left to process. 134 ldq $1, 8($0) # L : 135 subq $5, 1, $18 # E : U L U L 136 137 addq $0, 8, $0 # E : 138 # Make $18 point to last quad to be accessed (the 139 # last quad may or may not be partial). 140 andnot $18, 0x7, $18 # E : 141 cmpult $0, $18, $2 # E : 142 beq $2, $final # U : U L U L 143 144 # At least two quads remain to be accessed. 145 146 subq $18, $0, $4 # E : $4 <- nr quads to be processed 147 and $4, 8, $4 # E : odd number of quads? 148 bne $4, $odd_quad_count # U : 149 # At least three quads remain to be accessed 150 mov $1, $4 # E : L U L U : move prefetched value to correct reg 151 152 .align 4 153$unrolled_loop: 154 ldq $1, 8($0) # L : prefetch $1 155 xor $17, $4, $2 # E : 156 cmpbge $31, $2, $2 # E : 157 bne $2, $found_it # U : U L U L 158 159 addq $0, 8, $0 # E : 160 nop # E : 161 nop # E : 162 nop # E : 163 164$odd_quad_count: 165 xor $17, $1, $2 # E : 166 ldq $4, 8($0) # L : prefetch $4 167 cmpbge $31, $2, $2 # E : 168 addq $0, 8, $6 # E : 169 170 bne $2, $found_it # U : 171 cmpult $6, $18, $6 # E : 172 addq $0, 8, $0 # E : 173 nop # E : 174 175 bne $6, $unrolled_loop # U : 176 mov $4, $1 # E : move prefetched value into $1 177 nop # E : 178 nop # E : 179 180$final: subq $5, $0, $18 # E : $18 <- number of bytes left to do 181 nop # E : 182 nop # E : 183 bne $18, $last_quad # U : 184 185$not_found: 186 mov $31, $0 # E : 187 nop # E : 188 nop # E : 189 ret # L0 : 190 191 .end memchr 192