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https://issues.apache.org/jira/browse/MYNEWT-746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16037264#comment-16037264
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Sheela commented on MYNEWT-746:
-------------------------------
Need to document in release notes
> Sim - Floating point calculations sometimes incorrect
> -----------------------------------------------------
>
> Key: MYNEWT-746
> URL: https://issues.apache.org/jira/browse/MYNEWT-746
> Project: Mynewt
> Issue Type: Bug
> Security Level: Public(Viewable by anyone)
> Reporter: Christopher Collins
> Assignee: Christopher Collins
> Fix For: v1_1_0_rel
>
>
> *Note: this problem does not occur in OS X; it has only been seen in Linux.*
> In sim, some floating point calculations yield wildly incorrect results
> (usually 0 or NaN). The cause appears to be that the floating point
> registers are not restored when longjmp() is called. If subsequent code
> tries to use an intermediate value stored in a floating point register, the
> result is indeterminate.
> There is a gcc / clang compiler option which mostly solves this problem:
> *-ffloat-store*:
> {quote}
> -ffloat-store
> Do not store floating point variables in registers, and inhibit other
> options that might change whether a floating point value is taken from a
> register or memory.
> This option prevents undesirable excess precision on machines such as the
> 68000 where the floating registers (of the 68881) keep more precision than a
> double is supposed to have. Similarly for the x86 architecture. For most
> programs, the excess precision does only good, but a few programs rely on the
> precise definition of IEEE floating point. Use -ffloat-store for such
> programs, after modifying them to store all pertinent intermediate
> computations into variables.
> {quote}
> The problems disappeared when I started using this option. However, it seems
> there is still the occasional miscalculation, as a test failure just occurred
> due to an incorrect floating point value. In this case, assigning {{18.0}}
> to an int yielded the value {{-2147483648}}.
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