[Bug math/30993] New: feenableexcept, fedisableexcept are incomplete on m68k

[Bug math/30993] New: feenableexcept, fedisableexcept are incomplete on m68k

[bruno at clisp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30993

            Bug ID: 30993
           Summary: feenableexcept, fedisableexcept are incomplete on m68k
           Product: glibc
           Version: 2.37
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: bruno at clisp dot org
  Target Milestone: ---

When, on m68k, feenableexcept or fedisableexcept is called with an argument
that contained FE_INVALID, it changes only bit 13 of the floating-point control
register (fpcr).

However, the m68k fpcr has three bit positions for various types of invalid
operation:
  - bit 15 for branch/set on unordered
  - bit 14 for signaling not-a-number
  - bit 13 for operand error
Reference: https://www.nxp.com/docs/en/reference-manual/M68000PM.pdf section
1.2.2, page 1-5, figure 1-3.

But when an unordered comparison is executed, this counts as an IEEE 754
"Invalid Operation" as well.
Reference:
https://www.gnu.org/software/libc/manual/html_node/FP-Exceptions.html

And when a signalling NaN is used in a floating-point operation, this counts as
an IEEE 754 "Invalid Operation" as well.
Reference: https://en.wikipedia.org/wiki/NaN#Signaling_NaN

So, instead of setting/clearing only bit 13, these two functions should
set/clear all of bit 15, bit 14, bit 13 all together.

Disclaimer: I can't test this on real hardware; I'm looking only at the
specifications.

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[Bug math/30993] feenableexcept, fedisableexcept are incomplete on m68k

[bruno at clisp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30993

Bruno Haible <bruno at clisp dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
               Host|                            |m68k-linux-gnu

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[Bug math/30993] feenableexcept, fedisableexcept are incomplete on m68k

[bruno at clisp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30993

--- Comment #1 from Bruno Haible <bruno at clisp dot org> ---
Created attachment 15192
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15192&action=edit
proposed fix

Find attached a proposed fix (untested).

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