NAME

floor, floorf, floorl — floor function

SYNOPSIS

#include <math.h>

double floor(double x);
float floorf(float x);
long double floorl(long double x);


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.

These functions shall compute the largest integral value not greater than x.

^[MX] These functions may raise the inexact floating-point exception for finite non-integer arguments.

RETURN VALUE

^[MX] The returned value shall be independent of the current rounding direction mode and shall have the same sign as x.

Upon successful completion, these functions shall return the largest integral value not greater than x, expressed as a double, float, or long double, as appropriate for the return type of the function.

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

If x is ±0 or ±Inf, x shall be returned.

ERRORS

No errors are defined.

EXAMPLES

None.

APPLICATION USAGE

The integral value returned by these functions might not be expressible as an intmax_t. The return value should be tested before assigning it to an integer type to avoid the undefined results of an integer overflow.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

ceil, feclearexcept, fetestexcept, isnan

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

CHANGE HISTORY

First released in Issue 1. Derived from Issue 1 of the SVID.

Issue 5

The DESCRIPTION is updated to indicate how an application should check for an error. This text was previously published in the APPLICATION USAGE section.

Issue 6

The floorf() and floorl() functions are added for alignment with the ISO/IEC 9899:1999 standard.

The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 standard are marked.

Issue 7

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0141 [346] is applied.

Issue 8

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