mirror of
https://github.com/oasislinux/oasis.git
synced 2026-05-12 21:34:47 +02:00
Michael Forney
55 lines
1.2 KiB
C
55 lines
1.2 KiB
C
#include <stdint.h>
|
|
|
|
/*
|
|
* Find highest one bit set.
|
|
* Returns bit number + 1 of highest bit that is set, otherwise returns 0.
|
|
*/
|
|
int
|
|
highbit64(uint64_t i)
|
|
{
|
|
if (i == 0)
|
|
return (0);
|
|
|
|
static const char debruijn[64] = {
|
|
1, 36, 2, 57, 37, 22, 3, 61,
|
|
58, 50, 38, 32, 23, 17, 4, 62,
|
|
55, 59, 30, 53, 51, 45, 39, 33,
|
|
47, 27, 24, 18, 41, 12, 5, 63,
|
|
35, 56, 21, 60, 49, 31, 16, 54,
|
|
29, 52, 44, 46, 26, 40, 11, 34,
|
|
20, 48, 15, 28, 43, 25, 10, 19,
|
|
14, 42, 9, 13, 8, 7, 6, 64
|
|
};
|
|
i |= i >> 1;
|
|
i |= i >> 2;
|
|
i |= i >> 4;
|
|
i |= i >> 8;
|
|
i |= i >> 16;
|
|
i |= i >> 32;
|
|
return (debruijn[(i * 0x03F79C6D30BACA89) >> 58 & 0x3F]);
|
|
}
|
|
|
|
/*
|
|
* Find lowest one bit set.
|
|
* Returns bit number + 1 of lowest bit that is set, otherwise returns 0.
|
|
*/
|
|
int
|
|
lowbit64(uint64_t i)
|
|
{
|
|
if (i == 0)
|
|
return (0);
|
|
|
|
static const char debruijn[64] = {
|
|
1, 2, 37, 3, 58, 38, 23, 4,
|
|
62, 59, 51, 39, 33, 24, 18, 5,
|
|
63, 56, 60, 31, 54, 52, 46, 40,
|
|
34, 48, 28, 25, 19, 42, 13, 6,
|
|
64, 36, 57, 22, 61, 50, 32, 17,
|
|
55, 30, 53, 45, 47, 27, 41, 12,
|
|
35, 21, 49, 16, 29, 44, 26, 11,
|
|
20, 15, 43, 10, 14, 9, 8, 7,
|
|
};
|
|
i &= -i;
|
|
return (debruijn[(i * 0x03F79C6D30BACA89) >> 58 & 0x3F]);
|
|
}
|