newlib/libc/string/strlen.c

   1 /*
   2 FUNCTION
   3         <<strlen>>---character string length
   4
   5 INDEX
   6         strlen
   7
   8 SYNOPSIS
   9         #include <string.h>
  10         size_t strlen(const char *<[str]>);
  11
  12 DESCRIPTION
  13         The <<strlen>> function works out the length of the string
  14         starting at <<*<[str]>>> by counting chararacters until it
  15         reaches a <<NULL>> character.
  16
  17 RETURNS
  18         <<strlen>> returns the character count.
  19
  20 PORTABILITY
  21 <<strlen>> is ANSI C.
  22
  23 <<strlen>> requires no supporting OS subroutines.
  24
  25 QUICKREF
  26         strlen ansi pure
  27 */
  28
  29 #include <_ansi.h>
  30 #include <string.h>
  31 #include <limits.h>
  32
  33 #define LBLOCKSIZE   (sizeof (long))
  34 #define UNALIGNED(X) ((long)X & (LBLOCKSIZE - 1))
  35
  36 #if LONG_MAX == 2147483647L
  37 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  38 #else
  39 #if LONG_MAX == 9223372036854775807L
  40 /* Nonzero if X (a long int) contains a NULL byte. */
  41 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  42 #else
  43 #error long int is not a 32bit or 64bit type.
  44 #endif
  45 #endif
  46
  47 #ifndef DETECTNULL
  48 #error long int is not a 32bit or 64bit byte
  49 #endif
  50
  51 size_t
  52 strlen (const char *str)
  53 {
  54   const char *start = str;
  55
  56 #if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
  57   unsigned long *aligned_addr;
  58
  59   /* Align the pointer, so we can search a word at a time.  */
  60   while (UNALIGNED (str))
  61     {
  62       if (!*str)
  63         return str - start;
  64       str++;
  65     }
  66
  67   /* If the string is word-aligned, we can check for the presence of
  68      a null in each word-sized block.  */
  69   aligned_addr = (unsigned long *)str;
  70   while (!DETECTNULL (*aligned_addr))
  71     aligned_addr++;
  72
  73   /* Once a null is detected, we check each byte in that block for a
  74      precise position of the null.  */
  75   str = (char *) aligned_addr;
  76
  77 #endif /* not PREFER_SIZE_OVER_SPEED */
  78
  79   while (*str)
  80     str++;
  81   return str - start;
  82 }