payloads/libpayload/arch/x86/string.c

   1 /*
   2  * Copyright (C) 1991,1992,1993,1997,1998,2003, 2005 Free Software Foundation, Inc.
   3  * Copyright (c) 2011 The ChromiumOS Authors.
   4  *
   5  * This program is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU General Public License as
   7  * published by the Free Software Foundation; either version 2 of
   8  * the License, or (at your option) any later version.
   9  *
  10  * This program 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
  13  * GNU General Public License for more details.
  14  */
  15
  16 /* From glibc-2.14, sysdeps/i386/memset.c */
  17
  18 #include <stdint.h>
  19
  20 #include "string.h"
  21
  22 typedef uint32_t op_t;
  23
  24 void *memset(void *dstpp, int c, size_t len)
  25 {
  26         int d0;
  27         unsigned long int dstp = (unsigned long int) dstpp;
  28
  29         /* This explicit register allocation improves code very much indeed. */
  30         register op_t x asm("ax");
  31
  32         x = (unsigned char) c;
  33
  34         /* Clear the direction flag, so filling will move forward.  */
  35         asm volatile("cld");
  36
  37         /* This threshold value is optimal.  */
  38         if (len >= 12) {
  39                 /* Fill X with four copies of the char we want to fill with. */
  40                 x |= (x << 8);
  41                 x |= (x << 16);
  42
  43                 /* Adjust LEN for the bytes handled in the first loop.  */
  44                 len -= (-dstp) % sizeof(op_t);
  45
  46                 /*
  47                  * There are at least some bytes to set. No need to test for
  48                  * LEN == 0 in this alignment loop.
  49                  */
  50
  51                 /* Fill bytes until DSTP is aligned on a longword boundary. */
  52                 asm volatile(
  53                         "rep\n"
  54                         "stosb" /* %0, %2, %3 */ :
  55                         "=D" (dstp), "=c" (d0) :
  56                         "0" (dstp), "1" ((-dstp) % sizeof(op_t)), "a" (x) :
  57                         "memory");
  58
  59                 /* Fill longwords.  */
  60                 asm volatile(
  61                         "rep\n"
  62                         "stosl" /* %0, %2, %3 */ :
  63                         "=D" (dstp), "=c" (d0) :
  64                         "0" (dstp), "1" (len / sizeof(op_t)), "a" (x) :
  65                         "memory");
  66                 len %= sizeof(op_t);
  67         }
  68
  69         /* Write the last few bytes. */
  70         asm volatile(
  71                 "rep\n"
  72                 "stosb" /* %0, %2, %3 */ :
  73                 "=D" (dstp), "=c" (d0) :
  74                 "0" (dstp), "1" (len), "a" (x) :
  75                 "memory");
  76
  77         return dstpp;
  78 }
  79
  80 void *memcpy(void *dest, const void *src, size_t n)
  81 {
  82         unsigned long d0, d1, d2;
  83
  84         asm volatile(
  85                 "rep ; movsl\n\t"
  86                 "movl %4,%%ecx\n\t"
  87                 "rep ; movsb\n\t"
  88                 : "=&c" (d0), "=&D" (d1), "=&S" (d2)
  89                 : "0" (n >> 2), "g" (n & 3), "1" (dest), "2" (src)
  90                 : "memory"
  91         );
  92
  93         return dest;
  94 }