firmware/common/strlen.c

   1 /*
   2 FUNCTION
   3         <<strlen>>---character string length
   4
   5 INDEX
   6         strlen
   7
   8 ANSI_SYNOPSIS
   9         #include <string.h>
  10         size_t strlen(const char *<[str]>);
  11
  12 TRAD_SYNOPSIS
  13         #include <string.h>
  14         size_t strlen(<[str]>)
  15         char *<[src]>;
  16
  17 DESCRIPTION
  18         The <<strlen>> function works out the length of the string
  19         starting at <<*<[str]>>> by counting chararacters until it
  20         reaches a <<NULL>> character.
  21
  22 RETURNS
  23         <<strlen>> returns the character count.
  24
  25 PORTABILITY
  26 <<strlen>> is ANSI C.
  27
  28 <<strlen>> requires no supporting OS subroutines.
  29
  30 QUICKREF
  31         strlen ansi pure
  32 */
  33
  34 #include <_ansi.h>
  35 #include <string.h>
  36 #include <limits.h>
  37
  38 #define LBLOCKSIZE   (sizeof (long))
  39 #define UNALIGNED(X) ((long)X & (LBLOCKSIZE - 1))
  40
  41 #if LONG_MAX == 2147483647L
  42 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  43 #else
  44 #if LONG_MAX == 9223372036854775807L
  45 /* Nonzero if X (a long int) contains a NULL byte. */
  46 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  47 #else
  48 #error long int is not a 32bit or 64bit type.
  49 #endif
  50 #endif
  51
  52 #ifndef DETECTNULL
  53 #error long int is not a 32bit or 64bit byte
  54 #endif
  55
  56 size_t
  57 _DEFUN (strlen, (str),
  58         _CONST char *str) __attribute__ ((section (".icode")));
  59
  60 size_t
  61 _DEFUN (strlen, (str),
  62         _CONST char *str)
  63 {
  64 #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  65   _CONST char *start = str;
  66
  67   while (*str)
  68     str++;
  69
  70   return str - start;
  71 #else
  72   _CONST char *start = str;
  73   unsigned long *aligned_addr;
  74
  75   if (!UNALIGNED (str))
  76     {
  77       /* If the string is word-aligned, we can check for the presence of
  78          a null in each word-sized block.  */
  79       aligned_addr = (unsigned long*)str;
  80       while (!DETECTNULL (*aligned_addr))
  81         aligned_addr++;
  82
  83       /* Once a null is detected, we check each byte in that block for a
  84          precise position of the null.  */
  85       str = (char*)aligned_addr;
  86     }
  87
  88   while (*str)
  89     str++;
  90   return str - start;
  91 #endif /* not PREFER_SIZE_OVER_SPEED */
  92 }