ffs

Name

ffs, ffsl, fls, flsl
- find first bit set in a word

Library

libc.lib

Synopsis

#include <strings.h>

int ffs (int value);

int ffsl (long value);

int fls (int value);

int flsl (long value);

Return values

Detailed description

The ffs and ffsl functions find the first bit set in value and return the index of that bit.

The fls and flsl functions find the last bit set in value and return the index of that bit.

Bits are numbered starting from 1, starting at the right-most (least significant) bit. A return value of zero from any of these functions means that the argument was zero.

Examples

#include <string.h>
#include <stdio.h>
int main()
{
    int i = 0x10;
    int j = ffs(i);
    if(j == 5) printf("First bit position in 0x10 is %d\n",j);
    return 0;
}

Output

First bit position in 0x10 is 5

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