CloverBootloader/rEFIt_UEFI/PlatformEFI/posix/strlen.cpp
jief666 0a8f273560 Cleaning and improvement of PlatformPOSIX.
Create a PlatformPOSIX+EFI.
2021-05-05 13:20:40 +03:00

100 lines
3.3 KiB
C++
Executable File

//#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);
}
}
}
}