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.Dd April 8, 2011 .Dt FFS32 3 .Os .Sh NAME .Nm ffs32 , .Nm ffs64 , .Nm fls32 , .Nm fls64 .Nd find first or last bit set .Sh SYNOPSIS n sys/bitops.h .Ft int .Fn ffs32 "uint32_t n" .Ft int .Fn ffs64 "uint64_t n" .Ft int .Fn fls32 "uint32_t n" .Ft int .Fn fls64 "uint64_t n" .Sh DESCRIPTION The .Fn ffs32 and .Fn ffs64 functions find the first bit set in .Fa n and return the index of that bit. Conversely, the .Fn fls32 and .Fn fls64 functions find the last bit set in .Fa n , returning the index of the bit.
p
The search always starts from the bit 1 (the least significant bit).
If the argument
.Fa n
is zero, each function returns zero.
.Sh IMPLEMENTATION NOTES
The described functions are implemented as
.Em static inline
functions in the
n sys/bitops.h header.
The standard C library includes a more portable
.Xr ffs 3
for user applications.
XXX: It is noted in the CVS history of <sys/bitops.h> that MD-optimized
<machine/bitops.h> is a TODO. If those start to appear, note it here.
.Sh EXAMPLES
In the following example
.Va f = 3
and
.Va l = 7 :
d -literal -offset indent uint32_t n = 0x44; /* 01000100 */
int f, l;
f = ffs32(n);
l = fls32(n);
.Ed
.Sh SEE ALSO
.Xr bitops 3 ,
.Xr bits 3 ,
.Xr bitstring 3 ,
.Xr ffs 3 ,
.Xr setbit 9
.Sh HISTORY
These functions first appeared in
.Nx 5.0 .