| .\" Copyright 2001 Andries Brouwer <aeb@cwi.nl>. |
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| .TH CEIL 3 2021-03-22 "" "Linux Programmer's Manual" |
| .SH NAME |
| ceil, ceilf, ceill \- ceiling function: smallest integral value not |
| less than argument |
| .SH SYNOPSIS |
| .nf |
| .B #include <math.h> |
| .PP |
| .BI "double ceil(double " x ); |
| .BI "float ceilf(float " x ); |
| .BI "long double ceill(long double " x ); |
| .fi |
| .PP |
| Link with \fI\-lm\fP. |
| .PP |
| .RS -4 |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .RE |
| .PP |
| .BR ceilf (), |
| .BR ceill (): |
| .nf |
| _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L |
| || /* Since glibc 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE |
| .fi |
| .SH DESCRIPTION |
| These functions return the smallest integral value that is not less than |
| .IR x . |
| .PP |
| For example, |
| .IR ceil(0.5) |
| is 1.0, and |
| .IR ceil(\-0.5) |
| is 0.0. |
| .SH RETURN VALUE |
| These functions return the ceiling of |
| .IR x . |
| .PP |
| If |
| .I x |
| is integral, +0, \-0, NaN, or infinite, |
| .I x |
| itself is returned. |
| .SH ERRORS |
| No errors occur. |
| POSIX.1-2001 documents a range error for overflows, but see NOTES. |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR ceil (), |
| .BR ceilf (), |
| .BR ceill () |
| T} Thread safety MT-Safe |
| .TE |
| .hy |
| .ad |
| .sp 1 |
| .SH CONFORMING TO |
| C99, POSIX.1-2001, POSIX.1-2008. |
| .PP |
| The variant returning |
| .I double |
| also conforms to |
| SVr4, 4.3BSD, C89. |
| .SH NOTES |
| SUSv2 and POSIX.1-2001 contain text about overflow (which might set |
| .I errno |
| to |
| .BR ERANGE , |
| or raise an |
| .B FE_OVERFLOW |
| exception). |
| In practice, the result cannot overflow on any current machine, |
| so this error-handling stuff is just nonsense. |
| .\" The POSIX.1-2001 APPLICATION USAGE SECTION discusses this point. |
| (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 128 (respectively, 1024), |
| and the number of mantissa bits is 24 (respectively, 53).) |
| .PP |
| The integral value returned by these functions may be too large |
| to store in an integer type |
| .RI ( int , |
| .IR long , |
| etc.). |
| To avoid an overflow, which will produce undefined results, |
| an application should perform a range check on the returned value |
| before assigning it to an integer type. |
| .SH SEE ALSO |
| .BR floor (3), |
| .BR lrint (3), |
| .BR nearbyint (3), |
| .BR rint (3), |
| .BR round (3), |
| .BR trunc (3) |