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/*
* 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;
}
/**
* 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;
}
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