| 1 | /* strchrnul (str, ch) -- Return pointer to first occurrence of CH in STR |
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| 2 | or the final NUL byte. |
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| 3 | For Motorola 68000. |
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| 4 | Copyright (C) 1999-2024 Free Software Foundation, Inc. |
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| 5 | This file is part of the GNU C Library. |
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| 6 | |
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| 7 | The GNU C Library is free software; you can redistribute it and/or |
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| 8 | modify it under the terms of the GNU Lesser General Public |
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| 9 | License as published by the Free Software Foundation; either |
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| 10 | version 2.1 of the License, or (at your option) any later version. |
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| 11 | |
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| 12 | The GNU C Library is distributed in the hope that it will be useful, |
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| 13 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 15 | Lesser General Public License for more details. |
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| 16 | |
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| 17 | You should have received a copy of the GNU Lesser General Public |
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| 18 | License along with the GNU C Library. If not, see |
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| 19 | <https://www.gnu.org/licenses/>. */ |
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| 20 | |
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| 21 | #include <sysdep.h> |
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| 22 | #include "asm-syntax.h" |
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| 23 | |
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| 24 | TEXT |
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| 25 | ENTRY(__strchrnul) |
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| 26 | /* Save the callee-saved registers we use. */ |
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| 27 | movel R(d2),MEM_PREDEC(sp) |
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| 28 | cfi_adjust_cfa_offset (4) |
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| 29 | movel R(d3),MEM_PREDEC(sp) |
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| 30 | cfi_adjust_cfa_offset (4) |
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| 31 | cfi_rel_offset (R(d2), 4) |
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| 32 | cfi_rel_offset (R(d3), 0) |
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| 33 | |
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| 34 | /* Get string pointer and character. */ |
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| 35 | movel MEM_DISP(sp,12),R(a0) |
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| 36 | moveb MEM_DISP(sp,19),R(d0) |
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| 37 | |
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| 38 | /* Distribute the character to all bytes of a longword. */ |
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| 39 | movel R(d0),R(d1) |
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| 40 | lsll #8,R(d1) |
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| 41 | moveb R(d0),R(d1) |
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| 42 | movel R(d1),R(d0) |
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| 43 | swap R(d0) |
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| 44 | movew R(d1),R(d0) |
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| 45 | |
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| 46 | /* First search for the character one byte at a time until the |
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| 47 | pointer is aligned to a longword boundary. */ |
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| 48 | movel R(a0),R(d1) |
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| 49 | #ifdef __mcoldfire__ |
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| 50 | andl #3,R(d1) |
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| 51 | #else |
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| 52 | andw #3,R(d1) |
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| 53 | #endif |
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| 54 | beq L(L1) |
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| 55 | moveb MEM(a0),R(d2) |
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| 56 | cmpb R(d0),R(d2) |
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| 57 | beq L(L9) |
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| 58 | tstb R(d2) |
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| 59 | beq L(L9) |
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| 60 | addql #1,R(a0) |
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| 61 | |
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| 62 | #ifdef __mcoldfire__ |
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| 63 | subql #3,R(d1) |
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| 64 | #else |
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| 65 | subqw #3,R(d1) |
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| 66 | #endif |
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| 67 | beq L(L1) |
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| 68 | moveb MEM(a0),R(d2) |
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| 69 | cmpb R(d0),R(d2) |
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| 70 | beq L(L9) |
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| 71 | tstb R(d2) |
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| 72 | beq L(L9) |
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| 73 | addql #1,R(a0) |
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| 74 | |
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| 75 | #ifdef __mcoldfire__ |
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| 76 | addql #1,R(d1) |
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| 77 | #else |
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| 78 | addqw #1,R(d1) |
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| 79 | #endif |
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| 80 | beq L(L1) |
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| 81 | moveb MEM(a0),R(d2) |
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| 82 | cmpb R(d0),R(d2) |
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| 83 | beq L(L9) |
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| 84 | tstb R(d2) |
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| 85 | beq L(L9) |
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| 86 | addql #1,R(a0) |
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| 87 | |
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| 88 | L(L1:) |
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| 89 | /* Load the magic bits. Unlike the generic implementation we can |
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| 90 | use the carry bit as the fourth hole. */ |
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| 91 | movel #0xfefefeff,R(d3) |
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| 92 | |
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| 93 | /* We exit the loop if adding MAGIC_BITS to LONGWORD fails to |
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| 94 | change any of the hole bits of LONGWORD. |
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| 95 | |
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| 96 | 1) Is this safe? Will it catch all the zero bytes? |
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| 97 | Suppose there is a byte with all zeros. Any carry bits |
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| 98 | propagating from its left will fall into the hole at its |
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| 99 | least significant bit and stop. Since there will be no |
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| 100 | carry from its most significant bit, the LSB of the |
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| 101 | byte to the left will be unchanged, and the zero will be |
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| 102 | detected. |
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| 103 | |
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| 104 | 2) Is this worthwhile? Will it ignore everything except |
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| 105 | zero bytes? Suppose every byte of LONGWORD has a bit set |
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| 106 | somewhere. There will be a carry into bit 8. If bit 8 |
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| 107 | is set, this will carry into bit 16. If bit 8 is clear, |
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| 108 | one of bits 9-15 must be set, so there will be a carry |
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| 109 | into bit 16. Similarly, there will be a carry into bit |
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| 110 | 24. If one of bits 24-31 is set, there will be a carry |
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| 111 | into bit 32 (=carry flag), so all of the hole bits will |
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| 112 | be changed. |
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| 113 | |
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| 114 | 3) But wait! Aren't we looking for C, not zero? |
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| 115 | Good point. So what we do is XOR LONGWORD with a longword, |
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| 116 | each of whose bytes is C. This turns each byte that is C |
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| 117 | into a zero. */ |
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| 118 | |
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| 119 | L(L2:) |
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| 120 | /* Get the longword in question. */ |
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| 121 | movel MEM_POSTINC(a0),R(d1) |
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| 122 | /* XOR with the byte we search for. */ |
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| 123 | eorl R(d0),R(d1) |
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| 124 | |
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| 125 | /* Add the magic value. We get carry bits reported for each byte |
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| 126 | which is not C. */ |
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| 127 | movel R(d3),R(d2) |
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| 128 | addl R(d1),R(d2) |
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| 129 | |
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| 130 | /* Check the fourth carry bit before it is clobbered by the next |
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| 131 | XOR. If it is not set we have a hit. */ |
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| 132 | bcc L(L8) |
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| 133 | |
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| 134 | /* We are only interested in carry bits that change due to the |
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| 135 | previous add, so remove original bits. */ |
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| 136 | eorl R(d1),R(d2) |
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| 137 | |
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| 138 | /* Now test for the other three overflow bits. |
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| 139 | Set all non-carry bits. */ |
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| 140 | orl R(d3),R(d2) |
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| 141 | /* Add 1 to get zero if all carry bits were set. */ |
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| 142 | addql #1,R(d2) |
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| 143 | |
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| 144 | /* If we don't get zero then at least one byte of the word equals |
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| 145 | C. */ |
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| 146 | bne L(L8) |
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| 147 | |
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| 148 | /* Next look for a NUL byte. |
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| 149 | Restore original longword without reload. */ |
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| 150 | eorl R(d0),R(d1) |
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| 151 | /* Add the magic value. We get carry bits reported for each byte |
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| 152 | which is not NUL. */ |
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| 153 | movel R(d3),R(d2) |
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| 154 | addl R(d1),R(d2) |
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| 155 | |
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| 156 | /* Check the fourth carry bit before it is clobbered by the next |
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| 157 | XOR. If it is not set we have a hit. */ |
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| 158 | bcc L(L8) |
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| 159 | |
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| 160 | /* We are only interested in carry bits that change due to the |
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| 161 | previous add, so remove original bits. */ |
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| 162 | eorl R(d1),R(d2) |
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| 163 | |
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| 164 | /* Now test for the other three overflow bits. |
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| 165 | Set all non-carry bits. */ |
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| 166 | orl R(d3),R(d2) |
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| 167 | /* Add 1 to get zero if all carry bits were set. */ |
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| 168 | addql #1,R(d2) |
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| 169 | |
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| 170 | /* If we don't get zero then at least one byte of the word was |
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| 171 | NUL. Otherwise continue with the next longword. */ |
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| 172 | bne L(L8) |
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| 173 | |
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| 174 | /* Get the longword in question. */ |
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| 175 | movel MEM_POSTINC(a0),R(d1) |
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| 176 | /* XOR with the byte we search for. */ |
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| 177 | eorl R(d0),R(d1) |
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| 178 | |
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| 179 | /* Add the magic value. We get carry bits reported for each byte |
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| 180 | which is not C. */ |
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| 181 | movel R(d3),R(d2) |
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| 182 | addl R(d1),R(d2) |
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| 183 | |
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| 184 | /* Check the fourth carry bit before it is clobbered by the next |
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| 185 | XOR. If it is not set we have a hit. */ |
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| 186 | bcc L(L8) |
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| 187 | |
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| 188 | /* We are only interested in carry bits that change due to the |
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| 189 | previous add, so remove original bits */ |
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| 190 | eorl R(d1),R(d2) |
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| 191 | |
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| 192 | /* Now test for the other three overflow bits. |
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| 193 | Set all non-carry bits. */ |
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| 194 | orl R(d3),R(d2) |
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| 195 | /* Add 1 to get zero if all carry bits were set. */ |
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| 196 | addql #1,R(d2) |
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| 197 | |
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| 198 | /* If we don't get zero then at least one byte of the word equals |
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| 199 | C. */ |
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| 200 | bne L(L8) |
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| 201 | |
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| 202 | /* Next look for a NUL byte. |
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| 203 | Restore original longword without reload. */ |
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| 204 | eorl R(d0),R(d1) |
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| 205 | /* Add the magic value. We get carry bits reported for each byte |
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| 206 | which is not NUL. */ |
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| 207 | movel R(d3),R(d2) |
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| 208 | addl R(d1),R(d2) |
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| 209 | |
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| 210 | /* Check the fourth carry bit before it is clobbered by the next |
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| 211 | XOR. If it is not set we have a hit. */ |
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| 212 | bcc L(L8) |
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| 213 | |
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| 214 | /* We are only interested in carry bits that change due to the |
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| 215 | previous add, so remove original bits */ |
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| 216 | eorl R(d1),R(d2) |
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| 217 | |
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| 218 | /* Now test for the other three overflow bits. |
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| 219 | Set all non-carry bits. */ |
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| 220 | orl R(d3),R(d2) |
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| 221 | /* Add 1 to get zero if all carry bits were set. */ |
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| 222 | addql #1,R(d2) |
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| 223 | |
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| 224 | /* If we don't get zero then at least one byte of the word was |
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| 225 | NUL. Otherwise continue with the next longword. */ |
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| 226 | beq L(L2) |
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| 227 | |
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| 228 | L(L8:) |
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| 229 | /* We have a hit. Check to see which byte it was. First |
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| 230 | compensate for the autoincrement in the loop. */ |
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| 231 | subql #4,R(a0) |
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| 232 | |
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| 233 | moveb MEM(a0),R(d1) |
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| 234 | cmpb R(d0),R(d1) |
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| 235 | beq L(L9) |
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| 236 | tstb R(d1) |
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| 237 | beq L(L9) |
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| 238 | addql #1,R(a0) |
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| 239 | |
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| 240 | moveb MEM(a0),R(d1) |
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| 241 | cmpb R(d0),R(d1) |
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| 242 | beq L(L9) |
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| 243 | tstb R(d1) |
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| 244 | beq L(L9) |
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| 245 | addql #1,R(a0) |
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| 246 | |
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| 247 | moveb MEM(a0),R(d1) |
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| 248 | cmpb R(d0),R(d1) |
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| 249 | beq L(L9) |
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| 250 | tstb R(d1) |
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| 251 | beq L(L9) |
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| 252 | addql #1,R(a0) |
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| 253 | |
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| 254 | /* Otherwise the fourth byte must equal C or be NUL. */ |
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| 255 | L(L9:) |
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| 256 | movel R(a0),R(d0) |
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| 257 | movel MEM_POSTINC(sp),R(d3) |
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| 258 | cfi_adjust_cfa_offset (-4) |
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| 259 | cfi_restore (R(d3)) |
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| 260 | movel MEM_POSTINC(sp),R(d2) |
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| 261 | cfi_adjust_cfa_offset (-4) |
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| 262 | cfi_restore (R(d2)) |
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| 263 | rts |
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| 264 | END(__strchrnul) |
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| 265 | |
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| 266 | libc_hidden_def (__strchrnul) |
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| 267 | weak_alias (__strchrnul, strchrnul) |
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| 268 | |
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