strlen_32.c

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/*
 * Copyright 2010 Tilera Corporation. All Rights Reserved.
 *
 *   This program is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU General Public License
 *   as published by the Free Software Foundation, version 2.
 *
 *   This program is distributed in the hope that it will be useful, but
 *   WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
 *   NON INFRINGEMENT.  See the GNU General Public License for
 *   more details.
 */

#include <linux/types.h>
#include <linux/string.h>
#include <linux/module.h>

#undef strlen

size_t strlen(const char *s)
{
    /* Get an aligned pointer. */
    const uintptr_t s_int = (uintptr_t) s;
    const uint32_t *p = (const uint32_t *)(s_int & -4);

    /* Read the first word, but force bytes before the string to be nonzero.
     * This expression works because we know shift counts are taken mod 32.
     */
    uint32_t v = *p | ((1 << (s_int << 3)) - 1);

    uint32_t bits;
    while ((bits = __insn_seqb(v, 0)) == 0)
        v = *++p;

    return ((const char *)p) + (__insn_ctz(bits) >> 3) - s;
}
EXPORT_SYMBOL(strlen);