NAME

remquo, remquof, remquol — remainder functions

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);


DESCRIPTION

^[CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2024 defers to the ISO C standard.

The remquo(), remquof(), and remquol() functions shall compute the same remainder as the remainder(), remainderf(), and remainderl() functions, respectively. In the object pointed to by quo, they store a value whose sign is the sign of x/y and whose magnitude is congruent modulo 2ⁿ to the magnitude of the integral quotient of x/y, where n is an implementation-defined integer greater than or equal to 3. If y is zero, the value stored in the object pointed to by quo is unspecified.

An application wishing to check for error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

RETURN VALUE

These functions shall return x REM y.

^[MX] When subnormal results are supported, the returned value shall be exact.

If NaN is supported and a NaN is returned, the value stored in the object pointed to by quo is unspecified.

On systems that do not support the IEC 60559 Floating-Point option, if y is zero, it is implementation-defined whether a domain error occurs or zero is returned.

^[MX] If x or y is NaN, a NaN shall be returned.

If x is ±Inf or y is zero and the other argument is non-NaN, a domain error shall occur, and a NaN shall be returned.

ERRORS

These functions shall fail if:

Domain Error

^[MX] The x argument is ±Inf, or the y argument is ±0 and the other argument is non-NaN.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.

These functions may fail if:

Domain Error

The y argument is zero.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.

EXAMPLES

None.

APPLICATION USAGE

On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

RATIONALE

These functions are intended for implementing argument reductions which can exploit a few low-order bits of the quotient. Note that x may be so large in magnitude relative to y that an exact representation of the quotient is not practical.

FUTURE DIRECTIONS

None.

SEE ALSO

feclearexcept, fetestexcept, remainder

XBD 4.23 Treatment of Error Conditions for Mathematical Functions, <math.h>

CHANGE HISTORY

First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.

Issue 7

ISO/IEC 9899:1999 standard, Technical Corrigendum 2 #56 (SD5-XSH-ERN-83) is applied.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0507 [320] is applied.

Issue 8

Austin Group Defect 713 is applied, clarifying the behavior when a NaN is returned.

Austin Group Defect 1302 is applied, aligning these functions with the ISO/IEC 9899:2018 standard.