string/stpcpy.c

   1 /* Copyright (C) 1992-2024 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #define NO_MEMPCPY_STPCPY_REDIRECT
  19 #include <string.h>
  20 #include <stdint.h>
  21 #include <memcopy.h>
  22 #include <string-fzb.h>
  23 #include <string-misc.h>
  24
  25 #undef __stpcpy
  26 #undef stpcpy
  27
  28 #ifndef STPCPY
  29 # define STPCPY __stpcpy
  30 #endif
  31
  32 static __always_inline char *
  33 write_byte_from_word (op_t *dest, op_t word)
  34 {
  35   char *d = (char *) dest;
  36   for (size_t i = 0; i < OPSIZ; i++, ++d)
  37     {
  38       char c = extractbyte (word, i);
  39       *d = c;
  40       if (c == '\0')
  41         break;
  42     }
  43   return d;
  44 }
  45
  46 static __always_inline char *
  47 stpcpy_aligned_loop (op_t *restrict dst, const op_t *restrict src)
  48 {
  49   op_t word;
  50   while (1)
  51     {
  52       word = *src++;
  53       if (has_zero (word))
  54         break;
  55       *dst++ = word;
  56     }
  57
  58   return write_byte_from_word (dst, word);
  59 }
  60
  61 static __always_inline char *
  62 stpcpy_unaligned_loop (op_t *restrict dst, const op_t *restrict src,
  63                        uintptr_t ofs)
  64 {
  65   op_t w2a = *src++;
  66   uintptr_t sh_1 = ofs * CHAR_BIT;
  67   uintptr_t sh_2 = OPSIZ * CHAR_BIT - sh_1;
  68
  69   op_t w2 = MERGE (w2a, sh_1, (op_t)-1, sh_2);
  70   if (!has_zero (w2))
  71     {
  72       op_t w2b;
  73
  74       /* Unaligned loop.  The invariant is that W2B, which is "ahead" of W1,
  75          does not contain end-of-string.  Therefore it is safe (and necessary)
  76          to read another word from each while we do not have a difference.  */
  77       while (1)
  78         {
  79           w2b = *src++;
  80           w2 = MERGE (w2a, sh_1, w2b, sh_2);
  81           /* Check if there is zero on w2a.  */
  82           if (has_zero (w2))
  83             goto out;
  84           *dst++ = w2;
  85           if (has_zero (w2b))
  86             break;
  87           w2a = w2b;
  88         }
  89
  90       /* Align the final partial of P2.  */
  91       w2 = MERGE (w2b, sh_1, 0, sh_2);
  92     }
  93
  94 out:
  95   return write_byte_from_word (dst, w2);
  96 }
  97
  98
  99 /* Copy SRC to DEST, returning the address of the terminating '\0' in DEST.  */
 100 char *
 101 STPCPY (char *dest, const char *src)
 102 {
 103   /* Copy just a few bytes to make DEST aligned.  */
 104   size_t len = (-(uintptr_t) dest) % OPSIZ;
 105   for (; len != 0; len--, ++dest)
 106     {
 107       char c = *src++;
 108       *dest = c;
 109       if (c == '\0')
 110         return dest;
 111     }
 112
 113   /* DEST is now aligned to op_t, SRC may or may not be.  */
 114   uintptr_t ofs = (uintptr_t) src % OPSIZ;
 115   return ofs == 0 ? stpcpy_aligned_loop ((op_t*) dest, (const op_t *) src)
 116                   : stpcpy_unaligned_loop ((op_t*) dest,
 117                                            (const op_t *) (src - ofs) , ofs);
 118 }
 119 weak_alias (__stpcpy, stpcpy)
 120 libc_hidden_def (__stpcpy)
 121 libc_hidden_builtin_def (stpcpy)