# Category : C Source Code

Archive : ECSTR.ZIP

Filename : FFS.C

Author : Richard A. O'Keefe.

Updated: 20 April 1984

Defines: ffs(), ffc()

ffs(i) returns the index of the least significant 1 bit in i,

where 1 means the least significant bit and 32 means the

most significant bit, or returns -1 if i is 0.

ffc(i) returns the index of the least significant 0 bit in i,

where 1 means the least significant bit and 32 means the

most significant bit, or returns -1 if i is ~0.

These functions mimic the VAX FFS and FFC instructions, except that

the latter return much more sensible values. This file only exists

to make it easier to move 4.2bsd programs to System III (which is

rather like moving up from a Rolls Royce to a model T Ford), and so

I haven't bother with assembly code versions.

*/

#include "strings.h"

int ffs(i)

register int i;

{

register int N;

for (N = 8*sizeof(int); --N >= 0; i >>= 1)

if (i&1) return 8*sizeof(int)-N;

return -1;

}

int ffc(i)

register int i;

{

register int N;

for (N = 8*sizeof(int); --N >= 0; i >>= 1)

if (!(i&1)) return 8*sizeof(int)-N;

return -1;

}

Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

This is so awesome! 😀 I’d be cool if you could download an entire archive of this at once, though.

But one thing that puzzles me is the “mtswslnkmcjklsdlsbdmMICROSOFT” string. There is an article about it here. It is definitely worth a read: http://www.os2museum.com/wp/mtswslnk/