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Re: [Qemu-devel] [PATCH] fix fdiv instruction

From: Programmingkid
Subject: Re: [Qemu-devel] [PATCH] fix fdiv instruction
Date: Sun, 24 Jun 2018 09:46:12 -0400

> On Jun 24, 2018, at 12:18 AM, Richard Henderson <address@hidden> wrote:
> On 06/23/2018 01:17 PM, Programmingkid wrote:
>>>> https://www.pdfdrive.net/powerpc-microprocessor-family-the-programming-environments-for-32-e3087633.html
>>>> This document has the information on the fdiv. Page 133 has the 
>>>> information on what action is executed when a division by zero situation 
>>>> takes place. 
> Even in your referenced PDF, table 3-13, it says that frD is unmodified.

Actually it says when FPSCR[ZE] is set is when frD is unmodified. When 
FPSCR[ZE] is not set it frD's sign is determined by an XOR of the signs of the 
operands. I have verified that this is what happens on real PowerPC 750 and 950 

>>> struct sigaction a = { .sa_sigaction = handle, .sa_flags = SA_SIGINFO };
>>> sigaction(SIGFPE, &a, NULL);
>>> feenableexcept(FE_ALL_EXCEPT);
>> This is C99 code. There are a lot of floating point bugs with this 
>> implementation. I suggest all future testing be done using PowerPC assembly 
>> language only.
> Um.. have you really ever seen an implementation that won't set ZE?

I do know that when I did try to use C99 floating point code I saw a lot of 
problems. Bypassing any library issues by directly setting the FPSCR is best 
for testing. Table 2-4 in the pdf has information on the FPSCR. 

>> What compiler did you use to compile this program?
> gcc 7.2.
>> What operating system did you run this program on?
> CentOS 7, so kernel 3.10, glibc 2.17.
>> What are the specs of the system you used to test this program on?
> CHRP IBM,8231-E2B (Power7).

I was just wondering are you able to run a PowerPC operating system in QEMU in 
KVM mode on this Power7 computer?

Thank you.

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