FFS32(3) | Library Functions Manual | FFS32(3)

# NAME

ffs32, ffs64, fls32, fls64 — find first or last bit set

# SYNOPSIS

#include <sys/bitops.h>
int
ffs32(uint32_t n);
int
ffs64(uint64_t n);
int
fls32(uint32_t n);
int
fls64(uint64_t n);

# DESCRIPTION

The ffs32() and ffs64() functions find the first bit set in n and return the index of that bit. Conversely, the fls32() and fls64() functions find the last bit set in n, returning the index of the bit.
The search always starts from the bit 1 (the least significant bit). If the argument n is zero, each function returns zero.

# IMPLEMENTATION NOTES

The described functions are implemented as static inline functions in the <sys/bitops.h> header. The standard C library includes a more portable ffs(3) for user applications.

# EXAMPLES

In the following example f = 3 and l = 7:

    uint32_t n = 0x44;	/* 01000100 */
    int f, l;

    f = ffs32(n);
    l = fls32(n);

# SEE ALSO

bitops(3), bits(3), bitstring(3), ffs(3), setbit(9)

# HISTORY

These functions first appeared in NetBSD 5.0.

April 8, 2011 | NetBSD 8.2