sysdeps/i386/bzero.c

   1 /* bzero -- set a block of memory to zero.  For Intel 80x86, x>=3.
   2    This file is part of the GNU C Library.
   3    Copyright (C) 1991-2015 Free Software Foundation, Inc.
   4    Contributed by Torbjorn Granlund (tege@sics.se).
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <string.h>
  21 #include <memcopy.h>
  22
  23 #undef  bzero
  24 #undef  __bzero
  25
  26 #ifdef  __GNUC__
  27
  28 void
  29 __bzero (dstpp, len)
  30      void *dstpp;
  31      size_t len;
  32 {
  33   /* N.B.: This code is almost verbatim from memset.c.  */
  34   int d0;
  35   unsigned long int dstp = (unsigned long int) dstpp;
  36
  37   /* This explicit register allocation
  38      improves code very much indeed.  */
  39   register op_t x asm ("ax");
  40
  41   x = 0;
  42
  43   /* Clear the direction flag, so filling will move forward.  */
  44   asm volatile ("cld");
  45
  46   /* This threshold value is optimal.  */
  47   if (len >= 12)
  48     {
  49       /* Adjust LEN for the bytes handled in the first loop.  */
  50       len -= (-dstp) % OPSIZ;
  51
  52       /* There are at least some bytes to set.
  53          No need to test for LEN == 0 in this alignment loop.  */
  54
  55       /* Fill bytes until DSTP is aligned on a longword boundary.  */
  56       asm volatile ("rep\n"
  57                     "stosb" /* %0, %2, %3 */ :
  58                     "=D" (dstp), "=c" (d0) :
  59                     "0" (dstp), "1" ((-dstp) % OPSIZ), "a" (x) :
  60                     "memory");
  61
  62       /* Fill longwords.  */
  63       asm volatile ("rep\n"
  64                     "stosl" /* %0, %2, %3 */ :
  65                     "=D" (dstp), "=c" (d0) :
  66                     "0" (dstp), "1" (len / OPSIZ), "a" (x) :
  67                     "memory");
  68       len %= OPSIZ;
  69     }
  70
  71   /* Write the last few bytes.  */
  72   asm volatile ("rep\n"
  73                 "stosb" /* %0, %2, %3 */ :
  74                 "=D" (dstp), "=c" (d0) :
  75                 "0" (dstp), "c" (len), "a" (x) :
  76                 "memory");
  77 }
  78 weak_alias (__bzero, bzero)
  79
  80 #else
  81 #include <string/bzero.c>
  82 #endif