floor(3) Library Functions Manual floor(3)

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

Math library (libm, -lm)

#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

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.

These functions return the floor of x.

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

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

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

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

C11, POSIX.1-2008.

C99, POSIX.1-2001.

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

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).)

ceil(3), lrint(3), nearbyint(3), rint(3), round(3), trunc(3)

2024-05-02 Linux man-pages 6.8