clz.c

#include <stdio.h>
#include <stdint.h>


int iterative_clz(uint32_t x) {
    int n = 32, c = 16;
    do {
        uint32_t y = x >> c;
        if (y) { n -= c; x = y; }
        c >>= 1;
    } while (c);
    return (n - x);
}

int binary_clz(uint32_t x) {
    if (x == 0) return 32;
    int n = 0;
    if (x <= 0x0000FFFF) { n += 16; x <<= 16; }
    if (x <= 0x00FFFFFF) { n += 8; x <<= 8; }
    if (x <= 0x0FFFFFFF) { n += 4; x <<= 4; }
    if (x <= 0x3FFFFFFF) { n += 2; x <<= 2; }
    if (x <= 0x7FFFFFFF) { n += 1; x <<= 1; }
    return n;
}

int byte_clz(uint32_t x) {
    if (x == 0) return 32;
    int n = 1;
    if ((x >> 16) == 0) { n += 16; x <<= 16; }
    if ((x >> 24) == 0) { n += 8; x <<= 8; }
    if ((x >> 28) == 0) { n += 4; x <<= 4; }
    if ((x >> 30) == 0) { n += 2; x <<= 2; }
    n = n - (x >> 31);
    return n;
}

int recursive_clz(uint32_t x, int shift)
{
	if(x == 0)
		return 32;
	if(!shift) 
		return 0;

	uint16_t upper = (x >> shift); 
	uint16_t lower = (x & (0xFFFF >> (16 - shift)));
	return upper ? recursive_clz(upper,shift>>1) : shift + recursive_clz(lower,shift>>1);
}