floorf (3)
Leading comments
Copyright 2001 Andries Brouwer <aeb@cwi.nl>. and Copyright 2008, Linux Foundation, written by Michael Kerrisk <mtk.manpages@gmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived wor...
NAME
floor, floorf, floorl  largest integral value not greater than argumentSYNOPSIS
#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():

_BSD_SOURCE  _SVID_SOURCE  _XOPEN_SOURCE >= 600  _ISOC99_SOURCE 
_POSIX_C_SOURCE >= 200112L;
or cc std=c99
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.12001 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  MTSafe 
CONFORMING TO
C99, POSIX.12001, POSIX.12008.The variant returning double also conforms to SVr4, 4.3BSD, C89.