CloverBootloader/rEFIt_UEFI/PlatformEFI/posix/strlen.cpp

//#include <posix.h> // use angled, so posix.h will vary depending of the platform

#include <stdlib.h> // for abort
#include <stddef.h> // for size_t
#include <limits.h> // for SIZE_T_MAX
#include <string.h> // for strlen definition

#ifdef MAP_TO_EDK_STRLEN
extern "C" UINTN EFIAPI AsciiStrLen(IN CONST CHAR8 *String);
#endif

// Hope that unsigned long long is as big in bits sa a pointer difference.

#define DOWN_CAST_TO_SIZE_T(a) (  (uintptr_t)(a) > (uintptr_t)(SIZE_T_MAX) ? abort(), 0 : (size_t)(a)  )

/* Return the length of the null-terminated string STR.  Scan for
   the null terminator quickly by testing four bytes at a time.  */
size_t strlen (const char *str)
{
#ifdef MAP_TO_EDK_STRLEN
	return (size_t)(AsciiStrLen(str));
#endif

  const char *char_ptr;
  const unsigned long int *longword_ptr;
  unsigned long int longword, himagic, lomagic;

  /* Handle the first few characters by reading one character at a time.
     Do this until CHAR_PTR is aligned on a longword boundary.  */
  for (char_ptr = str; ((uintptr_t) char_ptr
                        & (sizeof (longword) - 1)) != 0;
       ++char_ptr)
    if (*char_ptr == '\0') {
      return DOWN_CAST_TO_SIZE_T(char_ptr - str);
	}

  /* All these elucidatory comments refer to 4-byte longwords,
     but the theory applies equally well to 8-byte longwords.  */

  longword_ptr = (unsigned long int *) char_ptr;

  /* Bits 31, 24, 16, and 8 of this number are zero.  Call these bits
     the "holes."  Note that there is a hole just to the left of
     each byte, with an extra at the end:

     bits:  01111110 11111110 11111110 11111111
     bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD

     The 1-bits make sure that carries propagate to the next 0-bit.
     The 0-bits provide holes for carries to fall into.  */
  himagic = 0x80808080L;
  lomagic = 0x01010101L;
  if (sizeof (longword) > 4)
    {
      /* 64-bit version of the magic.  */
      /* Do the shift in two steps to avoid a warning if long has 32 bits.  */
      himagic = ((himagic << 16) << 16) | himagic;
      lomagic = ((lomagic << 16) << 16) | lomagic;
    }
  if (sizeof (longword) > 8)
    abort ();

  /* Instead of the traditional loop which tests each character,
     we will test a longword at a time.  The tricky part is testing
     if *any of the four* bytes in the longword in question are zero.  */
  for (;;)
    {
      longword = *longword_ptr++;

      if (((longword - lomagic) & ~longword & himagic) != 0)
        {
          /* Which of the bytes was the zero?  If none of them were, it was
             a misfire; continue the search.  */

          const char *cp = (const char *) (longword_ptr - 1);

          if (cp[0] == 0)
            return DOWN_CAST_TO_SIZE_T(cp - str);
          if (cp[1] == 0)
            return DOWN_CAST_TO_SIZE_T(cp - str + 1);
          if (cp[2] == 0)
            return DOWN_CAST_TO_SIZE_T(cp - str + 2);
          if (cp[3] == 0)
            return DOWN_CAST_TO_SIZE_T(cp - str + 3);
          if (sizeof (longword) > 4)
            {
              if (cp[4] == 0)
                return DOWN_CAST_TO_SIZE_T(cp - str + 4);
              if (cp[5] == 0)
                return DOWN_CAST_TO_SIZE_T(cp - str + 5);
              if (cp[6] == 0)
                return DOWN_CAST_TO_SIZE_T(cp - str + 6);
              if (cp[7] == 0)
                return DOWN_CAST_TO_SIZE_T(cp - str + 7);
            }
        }
    }
}