* Bug in valarith.c:value_equal()?
@ 2005-02-08 10:11 Mark Kettenis
2005-02-08 15:46 ` Andrew Cagney
0 siblings, 1 reply; 3+ messages in thread
From: Mark Kettenis @ 2005-02-08 10:11 UTC (permalink / raw)
To: gdb
I've found the cause of the testsuite problems I reported yesterday.
The additional testsuite failures are intermittent. If you look
careful at the gdb.mi/mi-var-cmd.exp test you'll see that the test is
checking whether some uninitialized local variables have been changed.
The testsuite failures indicate that sometimes, the floating-point
variables change unexpectedly. Some further investigation showed that
these unexpected changes happened when the (unitialized) variables
were NaNs. All of a sudden things make sense. The variables don't
really change. GDB tries to determine whether a variable changes by
comparing its current value to a previous value. This is done by
calling valarith.c:value_equal(). For floating-point variables, this
function does the following check:
return value_as_double (arg1) == value_as_double (arg2);
Now in C this will return 0, if ARG1 and ARG2 are NaN, even if they
are bit for bit equal.
Actually I think the implementation of valarithm.c:value_equal() is
right; when GDB evaluates expressions NaN == NaN should be zero.
Therefore I think we shouldn't use this function when establishing
when a variable has been changed. Does it make sense to simply do a
bit-for-bit comparison in that case?
Mark
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Bug in valarith.c:value_equal()?
2005-02-08 10:11 Bug in valarith.c:value_equal()? Mark Kettenis
@ 2005-02-08 15:46 ` Andrew Cagney
2005-02-09 1:34 ` M.M. Kettenis
0 siblings, 1 reply; 3+ messages in thread
From: Andrew Cagney @ 2005-02-08 15:46 UTC (permalink / raw)
To: Mark Kettenis; +Cc: gdb
Mark Kettenis wrote:
Your right, varobj should use bitwise comparison. Suggest a function
value_content_equal.
Andrew
> I've found the cause of the testsuite problems I reported yesterday.
> The additional testsuite failures are intermittent. If you look
> careful at the gdb.mi/mi-var-cmd.exp test you'll see that the test is
> checking whether some uninitialized local variables have been changed.
> The testsuite failures indicate that sometimes, the floating-point
> variables change unexpectedly. Some further investigation showed that
> these unexpected changes happened when the (unitialized) variables
> were NaNs. All of a sudden things make sense. The variables don't
> really change. GDB tries to determine whether a variable changes by
> comparing its current value to a previous value. This is done by
> calling valarith.c:value_equal(). For floating-point variables, this
> function does the following check:
>
> return value_as_double (arg1) == value_as_double (arg2);
>
> Now in C this will return 0, if ARG1 and ARG2 are NaN, even if they
> are bit for bit equal.
>
> Actually I think the implementation of valarithm.c:value_equal() is
> right; when GDB evaluates expressions NaN == NaN should be zero.
> Therefore I think we shouldn't use this function when establishing
> when a variable has been changed. Does it make sense to simply do a
> bit-for-bit comparison in that case?
>
> Mark
>
>
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Bug in valarith.c:value_equal()?
2005-02-08 15:46 ` Andrew Cagney
@ 2005-02-09 1:34 ` M.M. Kettenis
0 siblings, 0 replies; 3+ messages in thread
From: M.M. Kettenis @ 2005-02-09 1:34 UTC (permalink / raw)
To: Andrew Cagney, Mark Kettenis, gdb
Andrew Cagney <cagney@gnu.org> wrote:
> Mark Kettenis wrote:
>
> Your right, varobj should use bitwise comparison. Suggest a function
> value_content_equal.
Consider it done. The varobj stuff does a lot of dancing to catch errors. I'll see if I can simplify that a bit, so it might take a few days.
Mark
^ permalink raw reply [flat|nested] 3+ messages in thread
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2005-02-08 10:11 Bug in valarith.c:value_equal()? Mark Kettenis
2005-02-08 15:46 ` Andrew Cagney
2005-02-09 1:34 ` M.M. Kettenis
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