62 lines
1.2 KiB
C
62 lines
1.2 KiB
C
|
///////////////////////////////////////////////////////////////////////////////
|
||
|
|
//
|
||
|
|
/// \file bsr.h
|
||
|
|
/// \brief Bit scan reverse
|
||
|
|
//
|
||
|
|
// This code has been put into the public domain.
|
||
|
|
//
|
||
|
|
// This library is distributed in the hope that it will be useful,
|
||
|
|
// but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
|
|
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
|
||
|
|
//
|
||
|
|
///////////////////////////////////////////////////////////////////////////////
|
||
|
|
|
||
|
|
#ifndef LZMA_BSR_H
|
||
|
|
#define LZMA_BSR_H
|
||
|
|
|
||
|
|
// NOTE: Both input and output variables for lzma_bsr must be uint32_t.
|
||
|
|
|
||
|
|
#if defined(__GNUC__) && (defined (HAVE_ASM_X86) || defined(HAVE_ASM_X86_64))
|
||
|
|
# define lzma_bsr(dest, n) \
|
||
|
|
__asm__("bsrl %1, %0" : "=r" (dest) : "rm" (n))
|
||
|
|
|
||
|
|
#else
|
||
|
|
# define lzma_bsr(dest, n) dest = lzma_bsr_helper(n)
|
||
|
|
|
||
|
|
static inline uint32_t
|
||
|
|
lzma_bsr_helper(uint32_t n)
|
||
|
|
{
|
||
|
|
assert(n != 0);
|
||
|
|
|
||
|
|
uint32_t i = 31;
|
||
|
|
|
||
|
|
if ((n & UINT32_C(0xFFFF0000)) == 0) {
|
||
|
|
n <<= 16;
|
||
|
|
i = 15;
|
||
|
|
}
|
||
|
|
|
||
|
|
if ((n & UINT32_C(0xFF000000)) == 0) {
|
||
|
|
n <<= 8;
|
||
|
|
i -= 8;
|
||
|
|
}
|
||
|
|
|
||
|
|
if ((n & UINT32_C(0xF0000000)) == 0) {
|
||
|
|
n <<= 4;
|
||
|
|
i -= 4;
|
||
|
|
}
|
||
|
|
|
||
|
|
if ((n & UINT32_C(0xC0000000)) == 0) {
|
||
|
|
n <<= 2;
|
||
|
|
i -= 2;
|
||
|
|
}
|
||
|
|
|
||
|
|
if ((n & UINT32_C(0x80000000)) == 0)
|
||
|
|
--i;
|
||
|
|
|
||
|
|
return i;
|
||
|
|
}
|
||
|
|
|
||
|
|
#endif
|
||
|
|
|
||
|
|
#endif
|