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Old 21 June 2018, 13:44   #1
PeterK
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FMOD and FREM are broken in 80 bit non-Jit

Sorry for finding this bug today after the release of 4.0.0, but FMOD and FREM which correspond with FPREM and FPREM1 on the x87 FPU are broken in the 80 bit non-Jit mode only, but not in 64 bit or Jit or softfloat. I wished I did that test 1 or 2 days ago.

-----------------

Btw, on my low-end Mini-PC with just 2*1MB cache for 4 CPU cores WinUAE sometimes gets relative sluggish when the Jit cache is set to more than 8 MB. This is not new since 4.0.0 and not a problem for me at all. I just mention it for the case that other users report similar issues and can't find the reason.
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Old 21 June 2018, 18:14   #2
Toni Wilen
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So whats the problem? I don't really care about those weird FPU instructions that no one uses anyway
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Old 21 June 2018, 21:01   #3
PeterK
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I wrote a small program to test my Pow(x,y) function which has a double loop for x and y to check all integer operands from 0 to 31 with positive or negative values for the base. So it runs from 0^0 to 31^31 and prints out all results. For negative base values in Pow() I have to check whether the exponent in FP1 is even or odd to set the sign for (-x)^oddy. This is done with
Code:
     FREM.S #2,FP1  ; or FMOD.S
     FBEQ.W even
     BSET.L #31,D0
even RTS
To reproduce this problem it should be enough to test with a few integer values for FPx from 0 to 5 and check the result of FREM.S #2,FPx and the condition code.

This works with all configs except 80 bit non-Jit. I noticed it because it needs a few loops before the Jit starts and the wrong results suddenly changed into correct values.
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Old 21 June 2018, 21:35   #4
Toni Wilen
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Parameters were swapped for x86 fprem and fprem1.. Fixed.
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Old 21 June 2018, 21:40   #5
PeterK
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Is WinUAE.7z updated with that fix?

Ok, test passed. Thanks.

Last edited by PeterK; 21 June 2018 at 22:13.
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Old 22 June 2018, 13:35   #6
Toni Wilen
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I thought I tested each fpu function with some simple tests but perhaps I used same value for both operands and assumed it worked if result was always zero
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