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NAME

copysign(), copysignf(), drem(), finite(), finitef(), logb(), scalb() − exponent manipulations

SYNOPSIS

#include <math.h>

double copysign(double x, double y);

double drem(double x, double y);

int finite(double x);

double logb(double x);

double scalb(double x, int n);

float copysignf(float x, float y);

int finitef(float x);

DESCRIPTION

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

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

drem() 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 ERRORS.

finite() returns 1 only when −INFINITY < x < +INFINITY. Otherwise it returns 0 (i.e., when |x| = INFINITY or x is NaN).

logb() returns x’s exponent n, a signed integer converted to double-precision floating point and chosen such that 1 ≤ |x|/2∗∗n < 2 unless x = 0 or (only on machines that conform to the IEEE -754 standard) |x| = INFINITY or x lies between 0 and the underflow threshold.

scalb() returns x∗(2∗∗n) computed, for integer n, without first computing 2∗∗n.

copysignf() and finitef() are float versions of copysign() and finite(). They are named in accordance with the conventions specified in the "Future Library Directions" section of the ANSI C standard. Programs must be compiled in ANSI mode (use the -Aa option) in order to use these functions; otherwise, the compiler promotes the float arguments to double, and the functions return incorrect results.

DEPENDENCIES

Series 300/400

These functions are not supported on Series 300/400 systems.

Series 700/800

These functions are provided in the PA1.1 versions of the math library only. The +DA1.1 option (the default on Series 700 systems) links in a PA1.1 version automatically. A PA1.1 library can be linked in explicitly. For more information, see the HP-UX Floating-Point Guide.

ERRORS

The IEEE -754 standard defines drem(x,0) and drem(INFINITY,y) to be invalid operations that produce a NaN.

The IEEE -754 standard defines logb(±INFINITY) = +INFINITY and logb(0) = −INFINITY, and requires the latter to signal a division-by-zero exception.

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