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/* integer_length_l - find most significant bit in an 'unsigned long'.
Copyright (C) 2011-2021 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program 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. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* Written by Bruno Haible <bruno@clisp.org>, 2011. */
#include <config.h>
/* Specification. */
#include "integer_length.h"
#include <limits.h>
#include <stddef.h>
#undef MIN
#define MIN(a,b) ((a) < (b) ? (a) : (b))
#ifdef USE_LONG_LONG
# define FUNC integer_length_ll
# define TYPE unsigned long long
# define GCC_BUILTIN __builtin_clzll
# ifdef _WIN64
# define MSVC_BUILTIN _BitScanReverse64
# endif
#else
# define FUNC integer_length_l
# define TYPE unsigned long
# define GCC_BUILTIN __builtin_clzl
# define MSVC_BUILTIN _BitScanReverse
#endif
#if defined _MSC_VER && !(__clang_major__ >= 4)
# include <intrin.h>
/* Copied from integer_length.c. */
static inline int
integer_length (unsigned int x)
{
/* _BitScanReverse
<https://docs.microsoft.com/en-us/cpp/intrinsics/bitscanreverse-bitscanreverse64> */
unsigned long bit;
if (_BitScanReverse (&bit, x))
return bit + 1;
else
return 0;
}
#endif
#define NBITS (sizeof (TYPE) * CHAR_BIT)
/* Modify shift count to be in bounds, even in dead code, otherwise GCC
emits warnings "right shift count >= width of type". */
#define MSC(i) MIN (i, NBITS - 1)
int
FUNC (TYPE x)
{
#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__clang_major__ >= 4)
if (x == 0)
return 0;
else
return NBITS - GCC_BUILTIN (x);
#elif defined _MSC_VER && defined MSVC_BUILTIN
/* _BitScanReverse, _BitScanReverse64
<https://docs.microsoft.com/en-us/cpp/intrinsics/bitscanreverse-bitscanreverse64> */
unsigned long bit;
if (MSVC_BUILTIN (&bit, x))
return bit + 1;
else
return 0;
#else
/* Split x into chunks, and look at one chunk after the other. */
if (sizeof (TYPE) > 2 * sizeof (unsigned int))
{
/* Generic loop. */
size_t i;
for (i = (sizeof (TYPE) - 1) / sizeof (unsigned int); i >= 2; i--)
{
unsigned int y = x >> (i * sizeof (unsigned int) * CHAR_BIT);
if (y != 0)
return i * sizeof (unsigned int) * CHAR_BIT + integer_length (y);
}
}
/* Unrolled the last 2 loop rounds. */
/* i = 1 */
if (sizeof (TYPE) > 1 * sizeof (unsigned int))
{
unsigned int y = x >> MSC (1 * sizeof (unsigned int) * CHAR_BIT);
if (y != 0)
return 1 * sizeof (unsigned int) * CHAR_BIT + integer_length (y);
}
/* i = 0 */
return integer_length ((unsigned int) x);
#endif
}
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