| 1 | /* rawmemchr (str, ch) -- Return pointer to first occurrence of CH in STR. |
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| 2 | For Motorola 68000. |
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| 3 | Copyright (C) 1999-2022 Free Software Foundation, Inc. |
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| 4 | This file is part of the GNU C Library. |
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| 5 | |
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| 6 | The GNU C Library is free software; you can redistribute it and/or |
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| 7 | modify it under the terms of the GNU Lesser General Public |
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| 8 | License as published by the Free Software Foundation; either |
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| 9 | version 2.1 of the License, or (at your option) any later version. |
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| 10 | |
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| 11 | The GNU C Library is distributed in the hope that it will be useful, |
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| 12 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 14 | Lesser General Public License for more details. |
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| 15 | |
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| 16 | You should have received a copy of the GNU Lesser General Public |
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| 17 | License along with the GNU C Library. If not, see |
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| 18 | <https://www.gnu.org/licenses/>. */ |
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| 19 | |
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| 20 | #include <sysdep.h> |
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| 21 | #include "asm-syntax.h" |
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| 22 | |
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| 23 | TEXT |
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| 24 | ENTRY(__rawmemchr) |
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| 25 | /* Save the callee-saved registers we use. */ |
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| 26 | movel R(d2),MEM_PREDEC(sp) |
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| 27 | cfi_adjust_cfa_offset (4) |
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| 28 | movel R(d3),MEM_PREDEC(sp) |
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| 29 | cfi_adjust_cfa_offset (4) |
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| 30 | cfi_rel_offset (R(d2), 4) |
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| 31 | cfi_rel_offset (R(d3), 0) |
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| 32 | |
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| 33 | /* Get string pointer and character. */ |
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| 34 | movel MEM_DISP(sp,12),R(a0) |
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| 35 | moveb MEM_DISP(sp,19),R(d0) |
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| 36 | |
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| 37 | /* Distribute the character to all bytes of a longword. */ |
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| 38 | movel R(d0),R(d1) |
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| 39 | lsll #8,R(d1) |
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| 40 | moveb R(d0),R(d1) |
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| 41 | movel R(d1),R(d0) |
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| 42 | swap R(d0) |
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| 43 | movew R(d1),R(d0) |
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| 44 | |
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| 45 | /* First search for the character one byte at a time until the |
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| 46 | pointer is aligned to a longword boundary. */ |
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| 47 | movel R(a0),R(d1) |
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| 48 | #ifdef __mcoldfire__ |
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| 49 | andl #3,R(d1) |
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| 50 | #else |
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| 51 | andw #3,R(d1) |
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| 52 | #endif |
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| 53 | beq L(L1) |
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| 54 | cmpb MEM(a0),R(d0) |
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| 55 | beq L(L9) |
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| 56 | addql #1,R(a0) |
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| 57 | |
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| 58 | #ifdef __mcoldfire__ |
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| 59 | subql #3,R(d1) |
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| 60 | #else |
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| 61 | subqw #3,R(d1) |
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| 62 | #endif |
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| 63 | beq L(L1) |
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| 64 | cmpb MEM(a0),R(d0) |
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| 65 | beq L(L9) |
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| 66 | addql #1,R(a0) |
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| 67 | |
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| 68 | #ifdef __mcoldfire__ |
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| 69 | addql #1,R(d1) |
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| 70 | #else |
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| 71 | addqw #1,R(d1) |
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| 72 | #endif |
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| 73 | beq L(L1) |
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| 74 | cmpb MEM(a0),R(d0) |
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| 75 | beq L(L9) |
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| 76 | addql #1,R(a0) |
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| 77 | |
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| 78 | L(L1:) |
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| 79 | /* Load the magic bits. Unlike the generic implementation we can |
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| 80 | use the carry bit as the fourth hole. */ |
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| 81 | movel #0xfefefeff,R(d3) |
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| 82 | |
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| 83 | /* We exit the loop if adding MAGIC_BITS to LONGWORD fails to |
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| 84 | change any of the hole bits of LONGWORD. |
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| 85 | |
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| 86 | 1) Is this safe? Will it catch all the zero bytes? |
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| 87 | Suppose there is a byte with all zeros. Any carry bits |
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| 88 | propagating from its left will fall into the hole at its |
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| 89 | least significant bit and stop. Since there will be no |
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| 90 | carry from its most significant bit, the LSB of the |
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| 91 | byte to the left will be unchanged, and the zero will be |
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| 92 | detected. |
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| 93 | |
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| 94 | 2) Is this worthwhile? Will it ignore everything except |
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| 95 | zero bytes? Suppose every byte of LONGWORD has a bit set |
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| 96 | somewhere. There will be a carry into bit 8. If bit 8 |
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| 97 | is set, this will carry into bit 16. If bit 8 is clear, |
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| 98 | one of bits 9-15 must be set, so there will be a carry |
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| 99 | into bit 16. Similarly, there will be a carry into bit |
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| 100 | 24. If one of bits 24-31 is set, there will be a carry |
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| 101 | into bit 32 (=carry flag), so all of the hole bits will |
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| 102 | be changed. |
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| 103 | |
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| 104 | 3) But wait! Aren't we looking for C, not zero? |
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| 105 | Good point. So what we do is XOR LONGWORD with a longword, |
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| 106 | each of whose bytes is C. This turns each byte that is C |
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| 107 | into a zero. */ |
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| 108 | |
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| 109 | L(L2:) |
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| 110 | /* Get the longword in question. */ |
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| 111 | movel MEM_POSTINC(a0),R(d1) |
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| 112 | /* XOR with the byte we search for. */ |
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| 113 | eorl R(d0),R(d1) |
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| 114 | |
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| 115 | /* Add the magic value. We get carry bits reported for each byte |
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| 116 | which is not C. */ |
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| 117 | movel R(d3),R(d2) |
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| 118 | addl R(d1),R(d2) |
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| 119 | |
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| 120 | /* Check the fourth carry bit before it is clobbered by the next |
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| 121 | XOR. If it is not set we have a hit. */ |
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| 122 | bcc L(L8) |
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| 123 | |
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| 124 | /* We are only interested in carry bits that change due to the |
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| 125 | previous add, so remove original bits. */ |
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| 126 | eorl R(d1),R(d2) |
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| 127 | |
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| 128 | /* Now test for the other three overflow bits. |
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| 129 | Set all non-carry bits. */ |
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| 130 | orl R(d3),R(d2) |
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| 131 | /* Add 1 to get zero if all carry bits were set. */ |
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| 132 | addql #1,R(d2) |
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| 133 | |
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| 134 | /* If we don't get zero then at least one byte of the word equals |
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| 135 | C. */ |
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| 136 | bne L(L8) |
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| 137 | |
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| 138 | /* Get the longword in question. */ |
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| 139 | movel MEM_POSTINC(a0),R(d1) |
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| 140 | /* XOR with the byte we search for. */ |
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| 141 | eorl R(d0),R(d1) |
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| 142 | |
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| 143 | /* Add the magic value. We get carry bits reported for each byte |
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| 144 | which is not C. */ |
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| 145 | movel R(d3),R(d2) |
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| 146 | addl R(d1),R(d2) |
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| 147 | |
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| 148 | /* Check the fourth carry bit before it is clobbered by the next |
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| 149 | XOR. If it is not set we have a hit. */ |
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| 150 | bcc L(L8) |
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| 151 | |
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| 152 | /* We are only interested in carry bits that change due to the |
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| 153 | previous add, so remove original bits */ |
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| 154 | eorl R(d1),R(d2) |
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| 155 | |
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| 156 | /* Now test for the other three overflow bits. |
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| 157 | Set all non-carry bits. */ |
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| 158 | orl R(d3),R(d2) |
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| 159 | /* Add 1 to get zero if all carry bits were set. */ |
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| 160 | addql #1,R(d2) |
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| 161 | |
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| 162 | /* If we don't get zero then at least one byte of the word equals |
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| 163 | C. */ |
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| 164 | beq L(L2) |
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| 165 | |
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| 166 | L(L8:) |
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| 167 | /* We have a hit. Check to see which byte it was. First |
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| 168 | compensate for the autoincrement in the loop. */ |
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| 169 | subql #4,R(a0) |
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| 170 | |
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| 171 | cmpb MEM(a0),R(d0) |
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| 172 | beq L(L9) |
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| 173 | addql #1,R(a0) |
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| 174 | |
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| 175 | cmpb MEM(a0),R(d0) |
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| 176 | beq L(L9) |
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| 177 | addql #1,R(a0) |
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| 178 | |
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| 179 | cmpb MEM(a0),R(d0) |
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| 180 | beq L(L9) |
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| 181 | addql #1,R(a0) |
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| 182 | |
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| 183 | /* Otherwise the fourth byte must equal C. */ |
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| 184 | L(L9:) |
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| 185 | movel R(a0),R(d0) |
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| 186 | movel MEM_POSTINC(sp),R(d3) |
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| 187 | cfi_adjust_cfa_offset (-4) |
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| 188 | cfi_restore (R(d3)) |
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| 189 | movel MEM_POSTINC(sp),R(d2) |
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| 190 | cfi_adjust_cfa_offset (-4) |
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| 191 | cfi_restore (R(d2)) |
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| 192 | rts |
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| 193 | END(__rawmemchr) |
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| 194 | |
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| 195 | libc_hidden_def (__rawmemchr) |
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| 196 | weak_alias (__rawmemchr, rawmemchr) |
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| 197 | |
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