floor(3) Library Functions Manual floor(3)

# NAME¶

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

# LIBRARY¶

Math library (libm, -lm)

# SYNOPSIS¶

`#include <math.h>`
```double floor(double x);
float floorf(float x);
long double floorl(long double x);```

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 <= 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

# STANDARDS¶

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

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

# 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 127 (respectively, 1023), and the number of mantissa bits including the implicit bit is 24 (respectively, 53).)