67 строки
1.9 KiB
C
67 строки
1.9 KiB
C
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/*
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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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#undef strchr
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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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