ieee_functions(3M)

NAME

ieee_functions, ilogb, isnan, copysign, fabs, fmod, nextafter, remainder, scalbn − appendix and related miscellaneous functions for IEEE arithmetic

SYNOPSIS

cc [ flag ... ] file ... −lm [ library ... ]

#include <math.h>

int ilogb(double x);

int isnan(double x);

double copysign(double x, double y);

double fabs(double x);

double fmod(double x, double y);

double nextafter(double x, double y);

double remainder(double x, double y);

double scalbn(double x, int n);

MT-LEVEL

MT-Safe

DESCRIPTION

Most of these functions provide capabilities required by ANSI/IEEE Std 754-1985 or suggested in its appendix.

ilogb(x) returns the unbiased exponent of x in integer format. ilogb(±∞) = +MAXINT and ilogb(0) = −MAXINT; <values.h> defines MAXINT as the largest int. ilogb(x) never generates an exception. When x is subnormal, ilogb(x) returns an exponent computed as if x were first normalized.

isnan(x) returns 1 if x is NaN; otherwise it returns 0.

copysign(x,y) returns a value with the magnitude of x and with the sign bit of y.

fabs(x) returns the absolute value of x.

nextafter(x,y) returns the next machine representable number from x in the direction y.

remainder(x,y) and fmod(x,y) return a remainder of x with respect to y; that is, the result r is one of the numbers that differ from x by an integral multiple of y. Thus (x−r)/y is an integral value, even though it might exceed MAXINT, the largest int defined in <values.h> if it were explicitly computed as an int. Both functions return one of the two such r smallest in magnitude. remainder(x,y) is the operation specified in ANSI/IEEE Std 754-1985; the result of fmod(x,y) may differ from remainder’s result by ±y. The magnitude of remainder’s result cannot exceed half that of y; its sign might not agree with either x or y. The magnitude of fmod’s result is less than that of y; its sign agrees with that of x. Neither function can generate an exception as long as both arguments are normal or subnormal.

remainder(x,0), fmod(x,0), remainder(∞,y), and fmod(∞,y) are invalid operations; in IEEE754 mode (i.e. the −xlibmieee cc compilation option), a NaN is returned.

scalbn(x,n) returns x∗2∗∗n computed by exponent manipulation rather than by actually performing an exponentiation or a multiplication. Thus

1 ≤ scalbn(fabs(x),−ilogb(x)) < 2

for every x except 0, ∞, and NaN.

RETURN VALUES

For exceptional cases, matherr(3M) tabulates the values to be returned as dictated by various Standards.

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