FLOOR

Section: POSIX Programmer's Manual (3P)
Updated: 2003
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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 non-zero, 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 non-zero, then errno shall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow floating-point 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 floating-point 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 non-zero.  

RATIONALE

None.  

FUTURE DIRECTIONS

None.  

SEE ALSO

ceil(), feclearexcept(), fetestexcept(), isnan(), the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions, <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) 2001-2003 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 original Standard can be obtained online at http://www.opengroup.org/unix/online.html .