remquo(), remquof(), remquol()

Updated: May 06, 2022

Compute the floating point remainder

Synopsis:

#include <math.h>

double remquo( double x, 
               double y,
               int *quo );

float remquof( float x, 
               float y,
               int *quo );

long double remquol( long double x, 
                     long double y,
                     int *quo );

Arguments:

x
The numerator of the division.
y
The denominator.
quo
A pointer to a location where the function can store the sign and at least the last three bits of x / y.

Library:

libm
The general-purpose math library.
libm-sve
(QNX Neutrino 7.1 or later) A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.

Your system requirements will determine how you should work with these libraries:

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.

Description:

The remquo(), remquof(), and remquol() functions compute the floating-point remainder of the division operation x / y, as remainder() does. Additionally, they store the sign and at least the three of the last bits of x / y in the location that quo points to, sufficient to determine the octant of the result within a period. The current rounding mode doesn't affect these functions.

These functions are useful when you're using periodic functions where the period is exactly representable as a floating-point value. For example, if you're calculating sin(πx) for a very large x, calling sin() directly may result in a large error; if you first reduce the function's argument with remquo(), you can use the low-order bits of the quotient to determine the sign and the octant of the result within the period, and use the remainder to calculate the value with high precision.

To check for error situations, use feclearexcept() and fetestexcept(). For example:

Returns:

The floating point remainder r = x - ny, where y is nonzero.

If: These functions return: Errors:
x is Inf NaN FE_INVALID
x or y is NaN NaN
x isn't NaN, and y is zero NaN FE_INVALID

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

Classification:

C11, POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler Yes
Signal handler Yes
Thread Yes