Bug 132158

Summary:	log function gives wrong value for number more than 10^308
Product:	[Applications] kcalc	Reporter:	Jagadish R <krshnam>
Component:	general	Assignee:	Evan Teran <evan.teran>
Status:	RESOLVED FIXED
Severity:	normal	CC:	chr_bl, david, evan.teran
Priority:	NOR
Version First Reported In:	unspecified
Target Milestone:	---
Platform:	unspecified
OS:	Linux
Latest Commit:	https://commits.kde.org/kcalc/2a05545830fdc9a2fe6a1d249d9eff52c53b7d1f	Version Fixed In:	19.08.0
Sentry Crash Report:

Description Jagadish R 2006-08-09 20:36:24 UTC

Version:           2.0.2 (using KDE 3.5.2, Gentoo)
Compiler:          gcc version 3.4.4 (Gentoo 3.4.4-r1, ssp-3.4.4-1.0, pie-8.7.8)
OS:                Linux (i686) release 2.6.15-gentoo-r1

log(10^m) = m. In kcalc if m is more than 308, log function gives the wrong answer. For example, Log(10^309) gives 1.797693134862315908e+308

Comment 1 Klaus Niederkrüger 2007-01-16 09:27:58 UTC

*** Bug 138168 has been marked as a duplicate of this bug. ***

Comment 2 Markus Grob 2008-02-28 21:17:42 UTC

I think this is, because the result is stored in a double and they have an upper limit from 1.79769313486231 57E+308.
I now, this isn't a solution, but a possible reason.

Comment 3 David Johnson 2008-12-09 05:14:24 UTC

Many functions use standard C math functions taking double values. The fix will require changes to the underlying math engine (currently based on libgmp).

Comment 4 Evan Teran 2013-01-14 22:04:53 UTC

The kcalc which will ship with KDE 4.10 has a newly rewritten knumber core library, which aims to make things simpler and easier to code with.

After the 4.10 release, I will start to work on using MPFR (A high precision math library which can do trig functions with GMP types). Some work has already been done in this area, but I wanted to minimize the changes in this release to make it easier to find any regressions. Hopefully the following release will have support for higher precision trig functions :-).

Comment 5 Christoph Feck 2019-06-23 10:22:49 UTC

Git commit 2a05545830fdc9a2fe6a1d249d9eff52c53b7d1f by Christoph Feck, on behalf of Marcelo Mariano.
Committed on 23/06/2019 at 10:21.
Pushed by cfeck into branch 'master'.

Use MPFR in knumber_float in order to improve floating-point precision
Related: bug 148357, bug 407318
FIXED-IN: 19.08.0

Differential Revision: https://phabricator.kde.org/D21495

M  +8    -0    CMakeLists.txt
M  +2    -2    knumber/knumber.cpp
M  +0    -3    knumber/knumber_base.h
M  +80   -415  knumber/knumber_float.cpp
M  +14   -8    knumber/knumber_float.h
M  +8    -1    knumber/knumber_integer.cpp
M  +3    -2    knumber/tests/CMakeLists.txt

https://commits.kde.org/kcalc/2a05545830fdc9a2fe6a1d249d9eff52c53b7d1f