fls64(3) [netbsd man page]

FFS32(3)						   BSD 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() func-
     tions 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 por-
     table 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.

BSD
								   April 8, 2011							       BSD

FAST_DIVIDE32(3)					   BSD Library Functions Manual 					  FAST_DIVIDE32(3)

NAME

     fast_divide32, fast_divide32_prepare, fast_remainder32 -- fast 32bit division and remainder

SYNOPSIS

     #include <sys/bitops.h>

     uint32_t
     fast_divide32(uint32_t v, uint32_t div, uint32_t m, uint8_t s1, uint8_t s2);

     uint32_t
     fast_remainder32(uint32_t v, uint32_t div, uint32_t m, uint8_t s1, uint8_t s2);

     void
     fast_divide32_prepare(uint32_t div, uint32_t *m, uint8_t *s1, uint8_t *s2);

DESCRIPTION

     The fast_divide32 and fast_remainder32 functions compute the equivalent of v / div and v % div using optimised CPU instructions.  The con-
     stants m, s1, and s2 must first be preset for a given value of div with the fast_divide32_prepare function.

RATIONALE

     These functions are useful for inner loops and other performance-sensitive tasks.	The functions expand to code that is typically slightly
     larger than a plain division instruction, but requires less time to execute.  The code for constant div arguments should be equivalent to the
     assembly created by GCC.

EXAMPLES

     The following example computes q = a / b and r = a % b:

	   uint32_t a, b, q, r, m;
	   uint8_t s1, s2;

	   fast_divide32_prepare(b, &m, &s1, &s2);

	   q = fast_divide32(a, b, m, s1, s2);
	   r = fast_remainder32(a, b, m, s1, s2);

SEE ALSO

     bitops(3), div(3), remainder(3)

     Torbjorn Granlund and Peter L. Montgomery, "Division by Invariant Integers Using Multiplication", ACM SIGPLAN Notices, Issue 6, Volume 29,
     http://gmplib.org/~tege/divcnst-pldi94.pdf, 61-72, June 1994.

HISTORY

     The fast_divide32 function appeared in NetBSD 6.0.

BSD
								   May 10, 2011 							       BSD