Legacy Document

ceil

You can use the ceil function to round a real number upward to the nearest integer value.

double_t ceil (double_t x);

x

Any floating-point number.

DESCRIPTION

The ceil function rounds its argument upward. This is an ANSI standard C library function. The result is returned in a floating-point data type.

This function is the same as performing the following code sequence:

r = fegetround();       /* save current rounding direction */
fesetround(FE_UPWARD);  /* round upward */
rint(x);                /* round to integer */
fesetround(r);          /* restore rounding direction */

EXCEPTIONS

When x is finite and nonzero, the result of $ceil(x)$ is exact.

SPECIAL CASES

Table 9-3 shows the results when the argument to the ceil function is a zero, a NaN, or an Infinity.

Special cases for the ceil function

Operation	Result	Exceptions raised
$ceil(+0)$	+0	None
$ceil(-0)$	$-0$	None
$ceil(NaN)$	NaN	None[14]
$ceil(+$ )	+	None
$ceil(-$ )	$-$	None

EXAMPLES

z = ceil(+INFINITY); /* z = +INFINITY because +INFINITY is already 
                        an integer value by definition. */
z = ceil(300.1);     /* z = 301.0 */
z = ceil(-300.1);    /* z = -300.0 */

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[14] If the NaN is a signaling NaN, the invalid exception is raised.