newlib/libc/string/memccpy.c

   1 /*
   2 FUNCTION
   3         <<memccpy>>---copy memory regions with end-token check
   4
   5 SYNOPSIS
   6         #include <string.h>
   7         void* memccpy(void *restrict <[out]>, const void *restrict <[in]>,
   8                       int <[endchar]>, size_t <[n]>);
   9
  10 DESCRIPTION
  11         This function copies up to <[n]> bytes from the memory region
  12         pointed to by <[in]> to the memory region pointed to by
  13         <[out]>.  If a byte matching the <[endchar]> is encountered,
  14         the byte is copied and copying stops.
  15
  16         If the regions overlap, the behavior is undefined.
  17
  18 RETURNS
  19         <<memccpy>> returns a pointer to the first byte following the
  20         <[endchar]> in the <[out]> region.  If no byte matching
  21         <[endchar]> was copied, then <<NULL>> is returned.
  22
  23 PORTABILITY
  24 <<memccpy>> is a GNU extension.
  25
  26 <<memccpy>> requires no supporting OS subroutines.
  27
  28         */
  29
  30 #include <_ansi.h>
  31 #include <stddef.h>
  32 #include <string.h>
  33 #include <limits.h>
  34
  35 /* Nonzero if either X or Y is not aligned on a "long" boundary.  */
  36 #define UNALIGNED(X, Y) \
  37   (((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1)))
  38
  39 /* How many bytes are copied each iteration of the word copy loop.  */
  40 #define LITTLEBLOCKSIZE (sizeof (long))
  41
  42 /* Threshhold for punting to the byte copier.  */
  43 #define TOO_SMALL(LEN)  ((LEN) < LITTLEBLOCKSIZE)
  44
  45 /* Macros for detecting endchar */
  46 #if LONG_MAX == 2147483647L
  47 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  48 #else
  49 #if LONG_MAX == 9223372036854775807L
  50 /* Nonzero if X (a long int) contains a NULL byte. */
  51 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  52 #else
  53 #error long int is not a 32bit or 64bit type.
  54 #endif
  55 #endif
  56
  57
  58 void *
  59 memccpy (void *__restrict dst0,
  60         const void *__restrict src0,
  61         int endchar0,
  62         size_t len0)
  63 {
  64
  65 #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  66   void *ptr = NULL;
  67   char *dst = (char *) dst0;
  68   char *src = (char *) src0;
  69   char endchar = endchar0 & 0xff;
  70
  71   while (len0--)
  72     {
  73       if ((*dst++ = *src++) == endchar)
  74         {
  75           ptr = dst;
  76           break;
  77         }
  78     }
  79
  80   return ptr;
  81 #else
  82   void *ptr = NULL;
  83   unsigned char *dst = dst0;
  84   const unsigned char *src = src0;
  85   long *aligned_dst;
  86   const long *aligned_src;
  87   unsigned char endchar = endchar0 & 0xff;
  88
  89   /* If the size is small, or either SRC or DST is unaligned,
  90      then punt into the byte copy loop.  This should be rare.  */
  91   if (!TOO_SMALL(len0) && !UNALIGNED (src, dst))
  92     {
  93       unsigned int i;
  94       unsigned long mask = 0;
  95
  96       aligned_dst = (long*)dst;
  97       aligned_src = (long*)src;
  98
  99       /* The fast code reads the ASCII one word at a time and only
 100          performs the bytewise search on word-sized segments if they
 101          contain the search character, which is detected by XORing
 102          the word-sized segment with a word-sized block of the search
 103          character and then detecting for the presence of NULL in the
 104          result.  */
 105       for (i = 0; i < LITTLEBLOCKSIZE; i++)
 106         mask = (mask << 8) + endchar;
 107
 108
 109       /* Copy one long word at a time if possible.  */
 110       while (len0 >= LITTLEBLOCKSIZE)
 111         {
 112           unsigned long buffer = (unsigned long)(*aligned_src);
 113           buffer ^=  mask;
 114           if (DETECTNULL (buffer))
 115             break; /* endchar is found, go byte by byte from here */
 116           *aligned_dst++ = *aligned_src++;
 117           len0 -= LITTLEBLOCKSIZE;
 118         }
 119
 120        /* Pick up any residual with a byte copier.  */
 121       dst = (unsigned char*)aligned_dst;
 122       src = (unsigned char*)aligned_src;
 123     }
 124
 125   while (len0--)
 126     {
 127       if ((*dst++ = *src++) == endchar)
 128         {
 129           ptr = dst;
 130           break;
 131         }
 132     }
 133
 134   return ptr;
 135 #endif /* not PREFER_SIZE_OVER_SPEED */
 136 }