mirror of
https://gitlab.nic.cz/labs/bird.git
synced 2024-09-18 19:35:20 +00:00
89 lines
2.1 KiB
C
89 lines
2.1 KiB
C
/*
|
|
* BIRD Library -- Generic Bit Operations
|
|
*
|
|
* (c) 1998 Martin Mares <mj@ucw.cz>
|
|
*
|
|
* Can be freely distributed and used under the terms of the GNU GPL.
|
|
*/
|
|
|
|
#include "nest/bird.h"
|
|
#include "bitops.h"
|
|
|
|
/**
|
|
* u32_mkmask - create a bit mask
|
|
* @n: number of bits
|
|
*
|
|
* u32_mkmask() returns an unsigned 32-bit integer which binary
|
|
* representation consists of @n ones followed by zeroes.
|
|
*/
|
|
u32
|
|
u32_mkmask(uint n)
|
|
{
|
|
return n ? ~((1 << (32 - n)) - 1) : 0;
|
|
}
|
|
|
|
/**
|
|
* u32_masklen - calculate length of a bit mask
|
|
* @x: bit mask
|
|
*
|
|
* This function checks whether the given integer @x represents
|
|
* a valid bit mask (binary representation contains first ones, then
|
|
* zeroes) and returns the number of ones or 255 if the mask is invalid.
|
|
*/
|
|
uint
|
|
u32_masklen(u32 x)
|
|
{
|
|
int l = 0;
|
|
u32 n = ~x;
|
|
|
|
if (n & (n+1)) return 255;
|
|
if (x & 0x0000ffff) { x &= 0x0000ffff; l += 16; }
|
|
if (x & 0x00ff00ff) { x &= 0x00ff00ff; l += 8; }
|
|
if (x & 0x0f0f0f0f) { x &= 0x0f0f0f0f; l += 4; }
|
|
if (x & 0x33333333) { x &= 0x33333333; l += 2; }
|
|
if (x & 0x55555555) l++;
|
|
if (x & 0xaaaaaaaa) l++;
|
|
return l;
|
|
}
|
|
|
|
/**
|
|
* u32_log2 - compute a binary logarithm.
|
|
* @v: number
|
|
*
|
|
* This function computes a integral part of binary logarithm of given
|
|
* integer @v and returns it. The computed value is also an index of the
|
|
* most significant non-zero bit position.
|
|
*/
|
|
|
|
u32
|
|
u32_log2(u32 v)
|
|
{
|
|
/* The code from http://www-graphics.stanford.edu/~seander/bithacks.html */
|
|
u32 r, shift;
|
|
r = (v > 0xFFFF) << 4; v >>= r;
|
|
shift = (v > 0xFF ) << 3; v >>= shift; r |= shift;
|
|
shift = (v > 0xF ) << 2; v >>= shift; r |= shift;
|
|
shift = (v > 0x3 ) << 1; v >>= shift; r |= shift;
|
|
r |= (v >> 1);
|
|
return r;
|
|
}
|
|
|
|
|
|
/**
|
|
* u32_bitflip - flips bits in number.
|
|
* @n: number
|
|
*
|
|
* This function flips bits in the given number such that MSB becomes LSB and vice versa.
|
|
*/
|
|
|
|
u32
|
|
u32_bitflip(u32 n)
|
|
{
|
|
n = ((n & 0xffff0000) >> 16) | ((n & 0x0000ffff) << 16);
|
|
n = ((n & 0xff00ff00) >> 8) | ((n & 0x00ff00ff) << 8);
|
|
n = ((n & 0xf0f0f0f0) >> 4) | ((n & 0x0f0f0f0f) << 4);
|
|
n = ((n & 0xcccccccc) >> 2) | ((n & 0x33333333) << 2);
|
|
n = ((n & 0xaaaaaaaa) >> 1) | ((n & 0x55555555) << 1);
|
|
return n;
|
|
}
|