floor, floorf, floorl — largest integral value not greater than argument

## Synopsis

```#include <math.h>

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

`Link with -lm.`

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

floorf(), floorl():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

## Description

These functions return the largest integral value that is not greater than x.

For example, floor(0.5) is 0.0, and floor(-0.5) is -1.0.

## Return Value

These functions return the floor of x.

If x is integral, +0, -0, NaN, or an infinity, x itself is returned.

## Errors

No errors occur. POSIX.1-2001 documents a range error for overflows, but see Notes.

## Attributes

For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
floor(), floorf(), floorl() Thread safety MT-Safe

## Conforming to

C99, POSIX.1-2001, POSIX.1-2008.

The variant returning double also conforms to SVr4, 4.3BSD, C89.

## Notes

SUSv2 and POSIX.1-2001 contain text about overflow (which might set errno to ERANGE, or raise an FE_OVERFLOW exception). In practice, the result cannot overflow on any current machine, so this error-handling stuff is just nonsense. (More precisely, overflow can happen only when the maximum value of the exponent is smaller than the number of mantissa bits. For the IEEE-754 standard 32-bit and 64-bit floating-point numbers the maximum value of the exponent is 128 (respectively, 1024), and the number of mantissa bits is 24 (respectively, 53).)