mirror of
https://gitlab.nic.cz/labs/bird.git
synced 2024-12-22 01:31:55 +00:00
48 lines
1.1 KiB
C
48 lines
1.1 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(unsigned 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 -1 if the mask is invalid.
|
|
*/
|
|
int
|
|
u32_masklen(u32 x)
|
|
{
|
|
int l = 0;
|
|
u32 n = ~x;
|
|
|
|
if (n & (n+1)) return -1;
|
|
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;
|
|
}
|