
FLOOR(3P) POSIX Programmer's Manual FLOOR(3P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of
this interface may differ (consult the corresponding Linux manual page for details of
Linux behavior), or the interface may not be implemented on Linux.
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
These functions shall compute the largest integral value not greater than x.
An application wishing to check for error situations should set errno to zero and call
feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non
zero or fetestexcept(FE_INVALID  FE_DIVBYZERO  FE_OVERFLOW  FE_UNDERFLOW) is nonzero,
an error has occurred.
RETURN VALUE
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.
If x is NaN, a NaN shall be returned.
If x is +0 or +Inf, x shall be returned.
If the correct value would cause overflow, a range error shall occur and floor(),
floorf(), and floorl() shall return the value of the macro HUGE_VAL, HUGE_VALF, and
HUGE_VALL, respectively.
ERRORS
These functions shall fail if:
Range Error
The result would cause an overflow.
If the integer expression (math_errhandling & MATH_ERRNO) is nonzero, then errno shall be
set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non
zero, then the overflow floatingpoint exception shall be raised.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The integral value returned by these functions might not be expressible as an int or long.
The return value should be tested before assigning it to an integer type to avoid the
undefined results of an integer overflow.
The floor() function can only overflow when the floatingpoint representation has
DBL_MANT_DIG > DBL_MAX_EXP.
On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling &
MATH_ERREXCEPT) are independent of each other, but at least one of them must be nonzero.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
ceil(), feclearexcept(), fetestexcept(), isnan(), the Base Definitions volume of
IEEE Std 1003.12001, Section 4.18, Treatment of Error Conditions for Mathematical Func
tions, <math.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology  Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 20012003 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee document. The orig
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 FLOOR(3P) 
