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Top Forums Shell Programming and Scripting printf (awk,perl,shell) float rounding issue Post 302715341 by Scrutinizer on Sunday 14th of October 2012 02:48:10 PM
Old 10-14-2012
Quote:
Originally Posted by Don Cragun
There are some statistics books that recommend rounding even values down (4.5 -> 4) and odd values up (5.5 -> 6) assuming that doing so will produce sums of rounded numbers closer to the value of the sums of the unrounded values. But I doubt that ksh is trying to provide that capability. I would guess that this could easily be caused by some programs using float, others using double, and still others using long double and having the process of converting 4.5 to the closest value in those formats sitting on opposite sides of the not quite exact value 4.5 representable in the various formats.
If it were something that is a random consquence of some conversion, then I think the rounding would not be as consistent as it is in those shells other than ksh... The rounding of half-integers are a special case and a choice needs to be made...

Apparently "round half to even" is the default and/or recommended way according to IEE754

Last edited by Scrutinizer; 10-14-2012 at 04:11 PM..
 

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ROUND(3)						   BSD Library Functions Manual 						  ROUND(3)

NAME
round, lround, llround -- round to integral value, regardless of rounding direction SYNOPSIS
#include <math.h> double round(double x); float roundf(float x); long int lround(double x); long int lroundf(float x); long long int llround(double x); long long int llroundf(float x); DESCRIPTION
The round() and roundf() functions return the integral value nearest to x rounding half-way cases away from zero, regardless of the current rounding direction. The lround() , lroundf() , llround() and llroundf() functions return the integral value nearest to x (rounding half-way cases away from zero, regardless of the current rounding direction) in the return formats specified. If the rounded value is outside the range of the return type, the numeric result is unspecified and the "invalid" floating-point exception is raised. A range error may occur if the magnitude of x is too large. SPECIAL VALUES
round(+-0) returns +-0. round(+-infinity) returns +-infinity. The round() functions may, but are not required to, raise the "inexact" floating-point exception for non-integer numeric arguments. The lround() and llround() functions need not raise the "inexact" floating-point exception for non-integer arguments that round to within the range of the return type. SEE ALSO
abs(3), fabs(3), ceil(3), floor(3), ieee(3), math(3), rint(3) STANDARDS
The round() , roundf() , lround() , lroundf() , llround() , and llroundf() functions conform to ISO/IEC 9899:1999(E). BSD
July 22, 2003 BSD
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