sysdeps/i386/memset.c

   1 /* Set a block of memory to some byte value.
   2    For Intel 80x86, x>=3.
   3    Copyright (C) 1991,1992,1993,1997,1998,2003 Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5    Contributed by Torbjorn Granlund (tege@sics.se).
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Lesser General Public
   9    License as published by the Free Software Foundation; either
  10    version 2.1 of the License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser General Public
  18    License along with the GNU C Library; if not, write to the Free
  19    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  20    02111-1307 USA.  */
  21
  22 #include <string.h>
  23 #include <memcopy.h>
  24
  25 #ifdef  __GNUC__
  26
  27 #undef memset
  28
  29 void *
  30 memset (void *dstpp, int c, size_t len)
  31 {
  32   int d0;
  33   unsigned long int dstp = (unsigned long int) dstpp;
  34
  35   /* This explicit register allocation
  36      improves code very much indeed.  */
  37   register op_t x asm("ax");
  38
  39   x = (unsigned char) c;
  40
  41   /* Clear the direction flag, so filling will move forward.  */
  42   asm volatile("cld");
  43
  44   /* This threshold value is optimal.  */
  45   if (len >= 12)
  46     {
  47       /* Fill X with four copies of the char we want to fill with.  */
  48       x |= (x << 8);
  49       x |= (x << 16);
  50
  51       /* Adjust LEN for the bytes handled in the first loop.  */
  52       len -= (-dstp) % OPSIZ;
  53
  54       /* There are at least some bytes to set.
  55          No need to test for LEN == 0 in this alignment loop.  */
  56
  57       /* Fill bytes until DSTP is aligned on a longword boundary.  */
  58       asm volatile("rep\n"
  59                    "stosb" /* %0, %2, %3 */ :
  60                    "=D" (dstp), "=c" (d0) :
  61                    "0" (dstp), "1" ((-dstp) % OPSIZ), "a" (x) :
  62                    "memory");
  63
  64       /* Fill longwords.  */
  65       asm volatile("rep\n"
  66                    "stosl" /* %0, %2, %3 */ :
  67                    "=D" (dstp), "=c" (d0) :
  68                    "0" (dstp), "1" (len / OPSIZ), "a" (x) :
  69                    "memory");
  70       len %= OPSIZ;
  71     }
  72
  73   /* Write the last few bytes.  */
  74   asm volatile("rep\n"
  75                "stosb" /* %0, %2, %3 */ :
  76                "=D" (dstp), "=c" (d0) :
  77                "0" (dstp), "1" (len), "a" (x) :
  78                "memory");
  79
  80   return dstpp;
  81 }
  82 libc_hidden_builtin_def (memset)
  83
  84 #else
  85 #include <sysdeps/generic/memset.c>
  86 #endif