firmware/libc/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 "config.h"
  35 #include "_ansi.h"
  36 #include <string.h>
  37 #include <limits.h>
  38
  39 #define LBLOCKSIZE   (sizeof (long))
  40 #define UNALIGNED(X) ((long)X & (LBLOCKSIZE - 1))
  41
  42 #if LONG_MAX == 2147483647L
  43 #define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
  44 #else
  45 #if LONG_MAX == 9223372036854775807L
  46 /* Nonzero if X (a long int) contains a NULL byte. */
  47 #define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
  48 #else
  49 #error long int is not a 32bit or 64bit type.
  50 #endif
  51 #endif
  52
  53 #ifndef DETECTNULL
  54 #error long int is not a 32bit or 64bit byte
  55 #endif
  56
  57 size_t
  58 _DEFUN (strlen, (str),
  59         _CONST char *str) ICODE_ATTR;
  60
  61 size_t
  62 _DEFUN (strlen, (str),
  63         _CONST char *str)
  64 {
  65 #if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  66   _CONST char *start = str;
  67
  68   while (*str)
  69     str++;
  70
  71   return str - start;
  72 #else
  73   _CONST char *start = str;
  74   unsigned long *aligned_addr;
  75
  76   if (!UNALIGNED (str))
  77     {
  78       /* If the string is word-aligned, we can check for the presence of
  79          a null in each word-sized block.  */
  80       aligned_addr = (unsigned long*)str;
  81       while (!DETECTNULL (*aligned_addr))
  82         aligned_addr++;
  83
  84       /* Once a null is detected, we check each byte in that block for a
  85          precise position of the null.  */
  86       str = (char*)aligned_addr;
  87     }
  88
  89   while (*str)
  90     str++;
  91   return str - start;
  92 #endif /* not PREFER_SIZE_OVER_SPEED */
  93 }