firmware/libc/memmove.c

   1 /*
   2 FUNCTION
   3         <<memmove>>---move possibly overlapping memory
   4
   5 INDEX
   6         memmove
   7
   8 ANSI_SYNOPSIS
   9         #include <string.h>
  10         void *memmove(void *<[dst]>, const void *<[src]>, size_t <[length]>);
  11
  12 TRAD_SYNOPSIS
  13         #include <string.h>
  14         void *memmove(<[dst]>, <[src]>, <[length]>)
  15         void *<[dst]>;
  16         void *<[src]>;
  17         size_t <[length]>;
  18
  19 DESCRIPTION
  20         This function moves <[length]> characters from the block of
  21         memory starting at <<*<[src]>>> to the memory starting at
  22         <<*<[dst]>>>. <<memmove>> reproduces the characters correctly
  23         at <<*<[dst]>>> even if the two areas overlap.
  24
  25
  26 RETURNS
  27         The function returns <[dst]> as passed.
  28
  29 PORTABILITY
  30 <<memmove>> is ANSI C.
  31
  32 <<memmove>> requires no supporting OS subroutines.
  33
  34 QUICKREF
  35         memmove ansi pure
  36 */
  37
  38 #include "config.h"
  39 #include <_ansi.h>
  40 #include <string.h>
  41
  42 /* Nonzero if either X or Y is not aligned on a "long" boundary.  */
  43 #define UNALIGNED(X, Y) \
  44   (((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1)))
  45
  46 /* How many bytes are copied each iteration of the 4X unrolled loop.  */
  47 #define BIGBLOCKSIZE    (sizeof (long) << 2)
  48
  49 /* How many bytes are copied each iteration of the word copy loop.  */
  50 #define LITTLEBLOCKSIZE (sizeof (long))
  51
  52 /* Threshhold for punting to the byte copier.  */
  53 #define TOO_SMALL(LEN)  ((LEN) < BIGBLOCKSIZE)
  54
  55 _PTR
  56 _DEFUN (memmove, (dst_void, src_void, length),
  57         _PTR dst_void _AND
  58         _CONST _PTR src_void _AND
  59         size_t length) ICODE_ATTR;
  60
  61 _PTR
  62 _DEFUN (memmove, (dst_void, src_void, length),
  63         _PTR dst_void _AND
  64         _CONST _PTR src_void _AND
  65         size_t length)
  66 {
  67 #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  68   char *dst = dst_void;
  69   _CONST char *src = src_void;
  70
  71   if (src < dst && dst < src + length)
  72     {
  73       /* Have to copy backwards */
  74       src += length;
  75       dst += length;
  76       while (length--)
  77         {
  78           *--dst = *--src;
  79         }
  80     }
  81   else
  82     {
  83       while (length--)
  84         {
  85           *dst++ = *src++;
  86         }
  87     }
  88
  89   return dst_void;
  90 #else
  91   char *dst = dst_void;
  92   _CONST char *src = src_void;
  93   long *aligned_dst;
  94   _CONST long *aligned_src;
  95   unsigned int   len =  length;
  96
  97   if (src < dst && dst < src + len)
  98     {
  99       /* Destructive overlap...have to copy backwards */
 100       src += len;
 101       dst += len;
 102       while (len--)
 103         {
 104           *--dst = *--src;
 105         }
 106     }
 107   else
 108     {
 109       /* Use optimizing algorithm for a non-destructive copy to closely
 110          match memcpy. If the size is small or either SRC or DST is unaligned,
 111          then punt into the byte copy loop.  This should be rare.  */
 112       if (!TOO_SMALL(len) && !UNALIGNED (src, dst))
 113         {
 114           aligned_dst = (long*)dst;
 115           aligned_src = (long*)src;
 116
 117           /* Copy 4X long words at a time if possible.  */
 118           while (len >= BIGBLOCKSIZE)
 119             {
 120               *aligned_dst++ = *aligned_src++;
 121               *aligned_dst++ = *aligned_src++;
 122               *aligned_dst++ = *aligned_src++;
 123               *aligned_dst++ = *aligned_src++;
 124               len -= BIGBLOCKSIZE;
 125             }
 126
 127           /* Copy one long word at a time if possible.  */
 128           while (len >= LITTLEBLOCKSIZE)
 129             {
 130               *aligned_dst++ = *aligned_src++;
 131               len -= LITTLEBLOCKSIZE;
 132             }
 133
 134           /* Pick up any residual with a byte copier.  */
 135           dst = (char*)aligned_dst;
 136           src = (char*)aligned_src;
 137         }
 138
 139       while (len--)
 140         {
 141           *dst++ = *src++;
 142         }
 143     }
 144
 145   return dst_void;
 146 #endif /* not PREFER_SIZE_OVER_SPEED */
 147 }