copysign, drem, finite, logb, scalb - copysign, remainder, exponent

#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;

These functions are required for, or recommended by the IEEE
standard 754 for floating-point arithmetic.

Copysign(x,y) returns x with its sign changed to y’s.

Drem(x,y) returns the remainder r := x - n*y where n is the integer
nearest the exact value of x/y; moreover if |n-x/y|=1/2 then n is
even. Consequently the remainder is computed exactly and |r| <=
|y|/2. But drem(x,0) is exceptional; see below under DIAGNOSTICS.

Finite(x) = 1 just when -infinity < x < +infinity,
= 0 otherwise (when |x| = infinity or x is NaN)

Logb(x) returns x’s exponent n, a signed integer converted to
double-precision floating-point and so chosen that 1 <= |x|/2**n <
2 unless x = 0, +-infinity or a NaN.

Scalb(x,n) = x*(2**n) computed, for integer n, without first
computing 2**n.

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.

floor(3), libm(3)

Kwok-Choi Ng