03-26-2009
From perlfaq
Quote:
Found in /usr/perl5/5.00503/pod/perlfaq4.pod
Does Perl have a round() function? What about ceil() and floor()? Trig functions?
Remember that int() merely truncates toward 0. For rounding to a
certain number of digits, sprintf() or printf() is usually the
easiest route.
printf("%.3f", 3.1415926535); # prints 3.142
The POSIX module (part of the standard perl distribution)
implements ceil(), floor(), and a number of other mathematical
and trigonometric functions.
use POSIX;
$ceil = ceil(3.5); # 4
$floor = floor(3.5); # 3
In 5.000 to 5.003 Perls, trigonometry was done in the
Math::Complex module. With 5.004, the Math::Trig module (part of
the standard perl distribution) implements the trigonometric
functions. Internally it uses the Math::Complex module and some
functions can break out from the real axis into the complex
plane, for example the inverse sine of 2.
Rounding in financial applications can have serious
implications, and the rounding method used should be specified
precisely. In these cases, it probably pays not to trust
whichever system rounding is being used by Perl, but to instead
implement the rounding function you need yourself.
To see why, notice how you'll still have an issue on half-way-
point alternation:
for ($i = 0; $i < 1.01; $i += 0.05) { printf "%.1f ",$i}
0.0 0.1 0.1 0.2 0.2 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.7 0.7
0.8 0.8 0.9 0.9 1.0 1.0
Don't blame Perl. It's the same as in C. IEEE says we have to do
this. Perl numbers whose absolute values are integers under
2**31 (on 32 bit machines) will work pretty much like
mathematical integers. Other numbers are not guaranteed.
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floor(3) Library Functions Manual floor(3)
NAME
floor, ceil, modf, nint, rint, trunc - Round floating-point numbers to floating-point integers, return the nearest integral value, and
truncate a floating-point number
LIBRARY
Math Library (libm.a)
SYNOPSIS
#include <math.h>
double floor (double x);
float floorf (float x);
long double floorl (long double x);
double ceil (double x);
float ceilf (float x);
long double ceill (long double x);
double modf (double x, double *n);
float modff (float x, float *n);
long double modfl (long double x, long double *n);
double nint (double x);
float nintf (float x);
long double nintl (long double x);
double rint (double x);
float rintf (float x);
long double rintl (long double x);
double trunc (double x);
float truncf (float x);
long double truncl (long double x);
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
floor(): XPG4
ceil(): XPG4
modf(): XPG4
rint(): XPG4-UNIX
Refer to the standards(5) reference page for more information about industry standards and associated tags.
DESCRIPTION
The floor(), floorf(), and floorl() functions return the largest floating-point integer value less than or equal to x.
The ceil(), ceilf(), and ceill() functions return the smallest floating-point integer value greater than or equal to x.
The modf(), modff(), and modfl() functions split a floating-point number x into a fractional part f and an integer part i such that |f| <
1.0 and (f + i) = x. Both f and i have the same sign as x. The modf(), modff(), and modfl() functions return f and store i into the loca-
tion pointed to by n.
The nint(), nintf(), and nintl() functions return the nearest integral value to x, except halfway cases are rounded to the integral value
larger in magnitude. This corresponds to the FORTRAN generic intrinsic function nint().
The rint(), rintf(), and rintl() functions round x to an integral value according to the current IEEE rounding direction specified by the
user.
The trunc(), truncf(), and truncl() functions truncate x to an integral value. delim off
floor(3)