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  1. /*
  2. FUNCTION
  3.         <<strncpy>>---counted copy string
  4.  
  5. INDEX
  6.         strncpy
  7.  
  8. ANSI_SYNOPSIS
  9.         #include <string.h>
  10.         char *strncpy(char *restrict <[dst]>, const char *restrict <[src]>,
  11.                       size_t <[length]>);
  12.  
  13. TRAD_SYNOPSIS
  14.         #include <string.h>
  15.         char *strncpy(<[dst]>, <[src]>, <[length]>)
  16.         char *<[dst]>;
  17.         char *<[src]>;
  18.         size_t <[length]>;
  19.  
  20. DESCRIPTION
  21.         <<strncpy>> copies not more than <[length]> characters from the
  22.         the string pointed to by <[src]> (including the terminating
  23.         null character) to the array pointed to by <[dst]>.  If the
  24.         string pointed to by <[src]> is shorter than <[length]>
  25.         characters, null characters are appended to the destination
  26.         array until a total of <[length]> characters have been
  27.         written.
  28.  
  29. RETURNS
  30.         This function returns the initial value of <[dst]>.
  31.  
  32. PORTABILITY
  33. <<strncpy>> is ANSI C.
  34.  
  35. <<strncpy>> requires no supporting OS subroutines.
  36.  
  37. QUICKREF
  38.         strncpy ansi pure
  39. */
  40.  
  41. #include <string.h>
  42. #include <limits.h>
  43.  
  44. /*SUPPRESS 560*/
  45. /*SUPPRESS 530*/
  46.  
  47. /* Nonzero if either X or Y is not aligned on a "long" boundary.  */
  48. #define UNALIGNED(X, Y) \
  49.   (((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1)))
  50.  
  51. #if LONG_MAX == 2147483647L
  52. #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  53. #else
  54. #if LONG_MAX == 9223372036854775807L
  55. /* Nonzero if X (a long int) contains a NULL byte. */
  56. #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  57. #else
  58. #error long int is not a 32bit or 64bit type.
  59. #endif
  60. #endif
  61.  
  62. #ifndef DETECTNULL
  63. #error long int is not a 32bit or 64bit byte
  64. #endif
  65.  
  66. #define TOO_SMALL(LEN) ((LEN) < sizeof (long))
  67.  
  68. char *
  69. _DEFUN (strncpy, (dst0, src0),
  70.         char *__restrict dst0 _AND
  71.         _CONST char *__restrict src0 _AND
  72.         size_t count)
  73. {
  74. #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  75.   char *dscan;
  76.   _CONST char *sscan;
  77.  
  78.   dscan = dst0;
  79.   sscan = src0;
  80.   while (count > 0)
  81.     {
  82.       --count;
  83.       if ((*dscan++ = *sscan++) == '\0')
  84.         break;
  85.     }
  86.   while (count-- > 0)
  87.     *dscan++ = '\0';
  88.  
  89.   return dst0;
  90. #else
  91.   char *dst = dst0;
  92.   _CONST char *src = src0;
  93.   long *aligned_dst;
  94.   _CONST long *aligned_src;
  95.  
  96.   /* If SRC and DEST is aligned and count large enough, then copy words.  */
  97.   if (!UNALIGNED (src, dst) && !TOO_SMALL (count))
  98.     {
  99.       aligned_dst = (long*)dst;
  100.       aligned_src = (long*)src;
  101.  
  102.       /* SRC and DEST are both "long int" aligned, try to do "long int"
  103.          sized copies.  */
  104.       while (count >= sizeof (long int) && !DETECTNULL(*aligned_src))
  105.         {
  106.           count -= sizeof (long int);
  107.           *aligned_dst++ = *aligned_src++;
  108.         }
  109.  
  110.       dst = (char*)aligned_dst;
  111.       src = (char*)aligned_src;
  112.     }
  113.  
  114.   while (count > 0)
  115.     {
  116.       --count;
  117.       if ((*dst++ = *src++) == '\0')
  118.         break;
  119.     }
  120.  
  121.   while (count-- > 0)
  122.     *dst++ = '\0';
  123.  
  124.   return dst0;
  125. #endif /* not PREFER_SIZE_OVER_SPEED */
  126. }
  127.