ieee(3m) ieee(3m)
Name
copysign, drem, finite, logb, scalb - copysign, remainder, exponent manipulations
Syntax
#include <math.h>
double copysign(x,y)
double x,y;
double drem(x,y)
double x,y;
int finite(x)
double x;
double logb(x)
double x;
double scalb(x,n)
double x;
int n;
Description
These functions are required, or recommended by the IEEE standard 754 for floating-point arithmetic.
The function returns x with its sign changed to y's.
The function returns the remainder r := x - n*y where n is the integer nearest the exact value of x/y. Additionally if |n-x/y|=1/2, then n
is even. Consequently the remainder is computed exactly and |r| <= |y|/2. Note that is the exception (see Diagnostics).
Finite(x) = 1 just when -infinity < x < +infinity,
= 0 otherwise (when |x| = infinity or x is NaN)
The a signed integer converted to double-precision floating-point and so chosen that 1 <= |x|/2**n < 2 unless x = 0 or |x| = infinity or x
lies between 0 and the Underflow Threshold.
Scalb(x,n) = x*(2**n) computed, for integer n, without first computing 2**N.
Diagnostics
IEEE 754 defines drem(x,0) and drem(infinity,y) to be invalid operations that produce a NaN.
IEEE 754 defines logb(+-infinity) = +infinity and logb(0) = -infinity, requires the latter to signal Division-by-Zero.
Restrictions
IEEE 754 currently specifies that logb(denormalized no.) = logb(tiniest normalized no. > 0) but the consensus has changed to the specifica-
tion in the new proposed IEEE standard p854, namely that logb(x) satisfy
1 <= scalb(|x|,-logb(x)) < Radix ... = 2 for IEEE 754
for every x except 0, infinity and NaN. Almost every program that assumes 754's specification will work correctly if logb follows 854's
specification instead.
IEEE 754 requires copysign(x,NaN) = +-x but says nothing else about the sign of a NaN.
See Also
floor(3M), fp_class(3), math(3M)
RISC ieee(3m)
