drem Subroutine

Purpose

Computes the IEEE Remainder as defined in the IEEE Floating-Point Standard.

Libraries

IEEE Math Library (libm.a) or System V Math Library (libmsaa.a)

Syntax

#include <math.h>

double drem ( x, y) double x, y;

Description

The drem subroutine calculates the remainder r equal to x minus n to the x power multiplied by y (r = x - n * y), where the n parameter is the integer nearest the exact value of x divided by y (x/y). If |n -x/y| = 1/2, then the n parameter is an even value. Therefore, the remainder is computed exactly, and the absolute value of r (|r|) is less than or equal to the absolute value of y divided by 2 (|y|/2).

The IEEE Remainder differs from the fmod subroutine in that the IEEE Remainder always returns an r parameter such that |r| is less than or equal to |y|/2, while FMOD returns an r such that |r| is less than or equal to |y|. The IEEE Remainder is useful for argument reduction for transcendental functions.

Note: Compile any routine that uses subroutines from the libm.a library with the -lm flag. For example: compile the drem.c file:

cc drem.c -lm

Note: For new development, the remainder subroutine is the preferred interface.

Parameters

Item	Description
x	Specifies double-precision floating-point value.
y	Specifies a double-precision floating-point value.

Return Values

The drem subroutine returns a NaNQ value for (x, 0) and (+/-INF, y).