Bug 1049658 - 64-bit version of DOSBox has inaccurate FPU emulation
Summary: 64-bit version of DOSBox has inaccurate FPU emulation
Keywords:
Status: CLOSED EOL
Alias: None
Product: Fedora
Classification: Fedora
Component: dosbox
Version: 24
Hardware: x86_64
OS: Linux
unspecified
medium
Target Milestone: ---
Assignee: Andreas Bierfert
QA Contact: Fedora Extras Quality Assurance
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2014-01-08 00:16 UTC by Nikolay Nikolov
Modified: 2017-08-08 11:44 UTC (History)
4 users (show)

Fixed In Version:
Clone Of:
Environment:
Last Closed: 2017-08-08 11:44:40 UTC
Type: Bug
Embargoed:


Attachments (Terms of Use)

Description Nikolay Nikolov 2014-01-08 00:16:49 UTC
Description of problem:

The x86_64 version of DOSBox uses SSE to emulate the x87 FPU. The problem with that is that the x87 FPU has 80-bit extended precision registers, while the SSE registers support only the standard 64-bit double precision floating point format, so this causes 80-bit floats to be rounded to 64-bit. Unfortunately, this breaks some DOS games and compilers, since they use the FPU to perform things like memory copy. Apparently, this was the fastest way to copy memory on the original Pentium processor and that's why it's used. Unfortunately, the rounding from 80-bit to 64-bit breaks it.

This issue was reported by me 2 years ago upstream here:

http://sourceforge.net/p/dosbox/bugs/369/

But unfortunately, the bug still remains open.

One possible solution to work around this problem in Fedora on x86_64 is to use the i386 version of DOSBox (similarly to how Fedora includes the 32-bit version of wine), so that's why I'm reporting it here.

Comment 1 Boris Gjenero 2015-01-26 03:34:00 UTC
This has been fixed in DOSBox r3851: http://sourceforge.net/p/dosbox/code-0/3851/. That change enables use of the x86 FPU in 64 bit mode. Running r3869, I am getting accurate results.

Comment 2 Fedora End Of Life 2015-05-29 10:22:45 UTC
This message is a reminder that Fedora 20 is nearing its end of life.
Approximately 4 (four) weeks from now Fedora will stop maintaining
and issuing updates for Fedora 20. It is Fedora's policy to close all
bug reports from releases that are no longer maintained. At that time
this bug will be closed as EOL if it remains open with a Fedora  'version'
of '20'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, simply change the 'version' 
to a later Fedora version.

Thank you for reporting this issue and we are sorry that we were not 
able to fix it before Fedora 20 is end of life. If you would still like 
to see this bug fixed and are able to reproduce it against a later version 
of Fedora, you are encouraged  change the 'version' to a later Fedora 
version prior this bug is closed as described in the policy above.

Although we aim to fix as many bugs as possible during every release's 
lifetime, sometimes those efforts are overtaken by events. Often a 
more recent Fedora release includes newer upstream software that fixes 
bugs or makes them obsolete.

Comment 3 Sidney Sedlak 2016-04-06 12:35:04 UTC
I can test it on F24, if it's still broken (which probably is, since the changelog only say Mass_Rebuild) so you may update the version to 24, where is a better chance to have this fixed than in F22...

Comment 4 Fedora End Of Life 2017-07-25 18:37:22 UTC
This message is a reminder that Fedora 24 is nearing its end of life.
Approximately 2 (two) weeks from now Fedora will stop maintaining
and issuing updates for Fedora 24. It is Fedora's policy to close all
bug reports from releases that are no longer maintained. At that time
this bug will be closed as EOL if it remains open with a Fedora  'version'
of '24'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, simply change the 'version'
to a later Fedora version.

Thank you for reporting this issue and we are sorry that we were not
able to fix it before Fedora 24 is end of life. If you would still like
to see this bug fixed and are able to reproduce it against a later version
of Fedora, you are encouraged  change the 'version' to a later Fedora
version prior this bug is closed as described in the policy above.

Although we aim to fix as many bugs as possible during every release's
lifetime, sometimes those efforts are overtaken by events. Often a
more recent Fedora release includes newer upstream software that fixes
bugs or makes them obsolete.

Comment 5 Fedora End Of Life 2017-08-08 11:44:40 UTC
Fedora 24 changed to end-of-life (EOL) status on 2017-08-08. Fedora 24 is
no longer maintained, which means that it will not receive any further
security or bug fix updates. As a result we are closing this bug.

If you can reproduce this bug against a currently maintained version of
Fedora please feel free to reopen this bug against that version. If you
are unable to reopen this bug, please file a new report against the
current release. If you experience problems, please add a comment to this
bug.

Thank you for reporting this bug and we are sorry it could not be fixed.


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