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/**
* @file bitops.h
* @brief Bit twiddling operations
*
* Bit twiddling shortcuts for various
* operations; see http://graphics.stanford.edu/%7Eseander/bithacks.html
* for details.
*/
#ifndef _BITOPS_H
#define _BITOPS_H
/**
* @brief Next power of 2
* @param x The number to be rounded
* @return the rounded number
*
* Rounds an unsigned integer up to the
* next power of 2; i.e. 2, 4, 8, 16, etc.
*/
static inline unsigned int next_power_of_2(unsigned int x)
{
x--;
x |= (x >> 1);
x |= (x >> 2);
x |= (x >> 4);
x |= (x >> 8);
x |= (x >> 16);
return ++x;
}
/**
* @brief Count bits set
* @param w Number in which to count bits
* @return The number of bits set
*
* Counts the number of bits in an unsigned int
* that are set to 1. So, for example, in the
* number 5, hich is 101 in binary, there are
* two bits set to 1.
*/
static inline unsigned int count_bits_set(unsigned int w)
{
/*
* This is faster, and runs in parallel
*/
const int S[] = {1, 2, 4, 8, 16};
const int B[] = {0x55555555, 0x33333333, 0x0F0F0F0F, 0x00FF00FF, 0x0000FFFF};
int c = w;
c = ((c >> S[0]) & B[0]) + (c & B[0]);
c = ((c >> S[1]) & B[1]) + (c & B[1]);
c = ((c >> S[2]) & B[2]) + (c & B[2]);
c = ((c >> S[3]) & B[3]) + (c & B[3]);
c = ((c >> S[4]) & B[4]) + (c & B[4]);
return c;
}
/**
* @brief Make even number macro
* @param x Number to make even
*
* Quick macro to make a number even, by
* forcing the rightmost bit to 0.
*/
#define make_even_number(x) ((x) &= ~0x1)
/**
* @brief Conditionally set flag macro
* @param number to set or unset flag in
* @param mask bitmask to be set or unset
* @param condition whether to set or unset the flag
*
* According to a condition, this macro will set or unset a
* particular flag in a number. It's a quick way of doing
* this:
* if (condition) number |= mask; else number &= ~mask;
*/
#define conditionally_set_flag(number, mask, condition) ((number) ^= (-(condition) ^ (number)) & (mask))
#endif /* _BITOPS_H */
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