ビット演算を使わずにビット演算する

bit.c

/* 決まったやり方がありそうだけど、適当にやる */

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <limits.h>
#include <assert.h>

#define BIT_M 32
#define N 10000

unsigned int
bit_not(unsigned int v)
{
	int i;
	unsigned int ret = 0;
	
	for (i = BIT_M; i >= 0; --i) {
		unsigned int c = (unsigned int)pow(2.0, i);
		if (v >= c) {
			v -= c;
		} else {
			ret += c;
		}
	}
	return ret;
}

unsigned int
bit_or(unsigned int v, unsigned int bits)
{
	int i;
	unsigned int ret = 0;
	
	for (i = BIT_M; i >= 0; --i) {
		unsigned int c = (unsigned int)pow(2.0, i);
		int on = 0;
		if (bits >= c) {
			bits -= c;
			on = 1;
		}
		if (v >= c) {
			v -= c;
			ret += c;
		} else {
			if (on) {
				ret += c;
			}
		}
	}
	return ret;
}

unsigned int
bit_and(unsigned int v, unsigned int bits)
{
	int i;
	unsigned int ret = 0;
	
	for (i = BIT_M; i >= 0; --i) {
		unsigned int c = (unsigned int)pow(2.0, i);
		int on = 0;
		if (bits >= c) {
			bits -= c;
			on = 1;
		}
		if (v >= c) {
			v -= c;
			if (on) {
				ret += c;
			}
		}
	}
	return ret;
}

unsigned int
bit_shift_right(unsigned int v, int n)
{
	unsigned int c = (unsigned int)pow(2.0, n);
	return v / c;
}

unsigned int
bit_shift_left(unsigned int v, int n)
{
	unsigned int c = (unsigned int)pow(2.0, n);
	return v * c;
}

int
main(void)
{
	unsigned int i;
	
	for (i = 0; i < N; ++i) {
		unsigned int bit = (unsigned int)(((double)rand() / RAND_MAX) * 32);
		unsigned int mask = (unsigned int)(((double)rand() / RAND_MAX) * INT_MAX);
		
		assert((i & mask) == bit_and(i, mask));
		assert((i | mask) == bit_or(i, mask));
		assert((~i) == bit_not(i));
		assert((i << bit) == bit_shift_left(i, bit));
		assert((i >> bit) == bit_shift_right(i, bit));
	}
	return 0;
}