FFS32(3) Library Functions Manual FFS32(3)
ffs32, ffs64, fls32, fls64 -- find first or last bit set
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.
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.
In the following example f = 3 and l = 7:
uint32_t n = 0x44; /* 01000100 */
int f, l;
f = ffs32(n);
l = fls32(n);
bitops(3), bits(3), bitstring(3), ffs(3), setbit(9)
These functions first appeared in NetBSD 5.0.
NetBSD 6.1.5 April 8, 2011 NetBSD 6.1.5