The Open Group Base Specifications Issue 7
IEEE Std 1003.1, 2013 Edition
Copyright © 2001-2013 The IEEE and The Open Group

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] [Option Start] 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.1-2008 defers to the ISO C standard. [Option End]

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

RETURN VALUE

[MX] [Option Start] The result shall have the same sign as x. [Option End]

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] [Option Start] If x is NaN, a NaN shall be returned.

If x is ±0 or ±Inf, x shall be returned. [Option End]

ERRORS

No errors are defined.


The following sections are informative.

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.

These functions may raise the inexact floating-point exception if the result differs in value from the argument.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

ceil, feclearexcept, fetestexcept, isnan

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.

End of informative text.

 

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