Updated: 2021/Apr/14

FFS32(3) Library Functions Manual FFS32(3)NAMEffs32,ffs64,fls32,fls64- find first or last bit setSYNOPSIS#include<sys/bitops.h>intffs32(uint32_t n); intffs64(uint64_t n); intfls32(uint32_t n); intfls64(uint64_t n);DESCRIPTIONTheffs32() andffs64() functions find the first bit set in n and return the index of that bit. Conversely, thefls32() andfls64() 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.IMPLEMENTATIONNOTESThe 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.EXAMPLESIn the following example f = 3 and l = 7: uint32_t n = 0x44; /* 01000100 */ int f, l; f = ffs32(n); l = fls32(n);SEEALSObitops(3), bits(3), bitstring(3), ffs(3), setbit(9)HISTORYThese functions first appeared in NetBSD 5.0. NetBSD 9.99 April 8, 2011 NetBSD 9.99