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/* pow2, Copyright (c) 2016 Dave Odell <dmo2118@gmail.com>
*
* Permission to use, copy, modify, distribute, and sell this software and its
* documentation for any purpose is hereby granted without fee, provided that
* the above copyright notice appear in all copies and that both that
* copyright notice and this permission notice appear in supporting
* documentation. No representations are made about the suitability of this
* software for any purpose. It is provided "as is" without express or
* implied warranty.
*/
#include "pow2.h"
#include <limits.h>
int
i_log2 (size_t x)
{
/* -1 works best for to_pow2. */
if (!x)
return -1;
/* GCC 3.4 also has this. */
# if defined __GNUC__ && __GNUC__ >= 4 || defined __clang__
return sizeof(long) * CHAR_BIT - __builtin_clzl(x) - 1;
# else
{
unsigned bits = sizeof(x) * CHAR_BIT;
size_t mask = (size_t)-1;
unsigned result = bits - 1;
while (bits) {
if (!(x & mask)) {
result -= bits;
x <<= bits;
}
bits >>= 1;
mask <<= bits;
}
return result;
}
# endif
}
size_t
to_pow2 (size_t x)
{
return !x ? 1 : 1 << (i_log2(x - 1) + 1);
}
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