1  /* Scan memory for a character.  Generic version
       2     Copyright (C) 1991-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library; if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  #include <libc-pointer-arith.h>
      20  #include <string-fzb.h>
      21  #include <string-fzc.h>
      22  #include <string-fzi.h>
      23  #include <string-shift.h>
      24  #include <string.h>
      25  
      26  #undef memchr
      27  
      28  #ifdef MEMCHR
      29  # define __memchr MEMCHR
      30  #endif
      31  
      32  static __always_inline const char *
      33  sadd (uintptr_t x, uintptr_t y)
      34  {
      35    return (const char *)(y > UINTPTR_MAX - x ? UINTPTR_MAX : x + y);
      36  }
      37  
      38  /* Search no more than N bytes of S for C.  */
      39  void *
      40  __memchr (void const *s, int c_in, size_t n)
      41  {
      42    if (__glibc_unlikely (n == 0))
      43      return NULL;
      44  
      45    /* Read the first word, but munge it so that bytes before the array
      46       will not match goal.  */
      47    const op_t *word_ptr = PTR_ALIGN_DOWN (s, sizeof (op_t));
      48    uintptr_t s_int = (uintptr_t) s;
      49  
      50    op_t word = *word_ptr;
      51    op_t repeated_c = repeat_bytes (c_in);
      52    /* Compute the address of the last byte taking in consideration possible
      53       overflow.  */
      54    const char *lbyte = sadd (s_int, n - 1);
      55    /* And also the address of the word containing the last byte. */
      56    const op_t *lword = (const op_t *) PTR_ALIGN_DOWN (lbyte, sizeof (op_t));
      57  
      58    find_t mask = shift_find (find_eq_all (word, repeated_c), s_int);
      59    if (mask != 0)
      60      {
      61        char *ret = (char *) s + index_first (mask);
      62        return (ret <= lbyte) ? ret : NULL;
      63      }
      64    if (word_ptr == lword)
      65      return NULL;
      66  
      67    word = *++word_ptr;
      68    while (word_ptr != lword)
      69      {
      70        if (has_eq (word, repeated_c))
      71  	return (char *) word_ptr + index_first_eq (word, repeated_c);
      72        word = *++word_ptr;
      73      }
      74  
      75    if (has_eq (word, repeated_c))
      76      {
      77        /* We found a match, but it might be in a byte past the end of the
      78  	 array.  */
      79        char *ret = (char *) word_ptr + index_first_eq (word, repeated_c);
      80        if (ret <= lbyte)
      81  	return ret;
      82      }
      83    return NULL;
      84  }
      85  #ifndef MEMCHR
      86  weak_alias (__memchr, memchr)
      87  libc_hidden_builtin_def (memchr)
      88  #endif