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Date: Mon, 29 Mar 1999 22:00:02 -0800 (PST)
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To: freebsd-bugs@FreeBSD.org
Cc: 
From: Dave Bodenstab <imdave@mcs.net>
Subject: Re: bin/10863: rint(3) returns erratic results
Reply-To: Dave Bodenstab <imdave@mcs.net>
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The following reply was made to PR bin/10863; it has been noted by GNATS.

From: Dave Bodenstab <imdave@mcs.net>
To: twp@rootsweb.com
Cc: FreeBSD-gnats-submit@FreeBSD.ORG
Subject: Re: bin/10863: rint(3) returns erratic results
Date: Mon, 29 Mar 1999 23:59:48 -0600

 twp@rootsweb.com wrote:
 > 
 > >Number:         10863
 > >Category:       bin
 > >Synopsis:       rint(3) returns erratic results
 > >Confidential:   yes
 > >Severity:       serious
 > >Priority:       low
 > >Responsible:    freebsd-bugs
 > >State:          open
 > >Quarter:
 > >Keywords:
 > >Date-Required:
 > >Class:          sw-bug
 > >Submitter-Id:   current-users
 > >Arrival-Date:   Mon Mar 29 14:20:01 PST 1999
 > >Closed-Date:
 > >Last-Modified:
 > >Originator:     Tim Pierce
 > >Release:        FreeBSD 2.2.7-RELEASE i386
 > >Organization:
 > RootsWeb Genealogical Data Cooperative
 > >Environment:
 > 
 > 
 > 
 > >Description:
 > 
 > rint(3) appears to return inconsistent results for some inputs.  For
 > example, it rounds both 5.5 and 6.5 to 6.  If rint always rounds up,
 > it should round these numbers to 6 and 7; if it always rounds down, it
 > should round these numbers to 5 and 6; if it always rounds to the
 > nearest integer, it should round to 6 and 7.  Is there any situation
 > where it would be correct to round both 5.5 and 6.5 to 6?
 > 
 > >How-To-Repeat:
 > 
 > #include <math.h>
 > 
 > main()
 > {
 >     printf ("%f\n", rint(5.5));
 >     printf ("%f\n", rint(6.5));
 > }
 > 
 > >Fix:
 
 See ieeefp.h and floatingpoint.h: this is the correct behaviour
 for the default rounding mode of `round to nearest'.  See the
 Intel manuals for the exact definition of each rounding mode...
 briefly, round to nearest chooses the even number if the difference
 to the next higher/lower integer is the same.
 
 Change your program to the following and inspect the results.
 
 #include <math.h>
 #include <floatingpoint.h>
 
 main()
 {
   printf( "FP_RN:\n" );
   fpsetround( FP_RN );
   printf ("%f\n", rint(5.5));
   printf ("%f\n", rint(6.5));
 
   printf( "FP_RM:\n" );
   fpsetround( FP_RM );
   printf ("%f\n", rint(5.5));
   printf ("%f\n", rint(6.5));
 
   printf( "FP_RP:\n" );
   fpsetround( FP_RP );
   printf ("%f\n", rint(5.5));
   printf ("%f\n", rint(6.5));
 
   printf( "FP_RZ:\n" );
   fpsetround( FP_RZ );
   printf ("%f\n", rint(5.5));
   printf ("%f\n", rint(6.5));
 }
 
 Dave Bodenstab
 imdave@mcs.net
 


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