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64 lines
1.9 KiB
64 lines
1.9 KiB
/* |
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* Copyright 2010 Tilera Corporation. All Rights Reserved. |
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* |
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* This program is free software; you can redistribute it and/or |
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* modify it under the terms of the GNU General Public License |
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* as published by the Free Software Foundation, version 2. |
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* |
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* This program is distributed in the hope that it will be useful, but |
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* WITHOUT ANY WARRANTY; without even the implied warranty of |
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* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or |
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* NON INFRINGEMENT. See the GNU General Public License for |
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* more details. |
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*/ |
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#include <linux/types.h> |
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#include <linux/string.h> |
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#include <linux/module.h> |
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char *strchr(const char *s, int c) |
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{ |
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int z, g; |
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/* Get an aligned pointer. */ |
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const uintptr_t s_int = (uintptr_t) s; |
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const uint32_t *p = (const uint32_t *)(s_int & -4); |
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/* Create four copies of the byte for which we are looking. */ |
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const uint32_t goal = 0x01010101 * (uint8_t) c; |
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/* Read the first aligned word, but force bytes before the string to |
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* match neither zero nor goal (we make sure the high bit of each |
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* byte is 1, and the low 7 bits are all the opposite of the goal |
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* byte). |
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* |
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* Note that this shift count expression works because we know shift |
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* counts are taken mod 32. |
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*/ |
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const uint32_t before_mask = (1 << (s_int << 3)) - 1; |
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uint32_t v = (*p | before_mask) ^ (goal & __insn_shrib(before_mask, 1)); |
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uint32_t zero_matches, goal_matches; |
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while (1) { |
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/* Look for a terminating '\0'. */ |
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zero_matches = __insn_seqb(v, 0); |
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/* Look for the goal byte. */ |
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goal_matches = __insn_seqb(v, goal); |
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if (__builtin_expect(zero_matches | goal_matches, 0)) |
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break; |
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v = *++p; |
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} |
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z = __insn_ctz(zero_matches); |
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g = __insn_ctz(goal_matches); |
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/* If we found c before '\0' we got a match. Note that if c == '\0' |
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* then g == z, and we correctly return the address of the '\0' |
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* rather than NULL. |
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*/ |
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return (g <= z) ? ((char *)p) + (g >> 3) : NULL; |
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} |
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EXPORT_SYMBOL(strchr);
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