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From: | Richard Henderson |
Subject: | Re: [Qemu-devel] [PATCH v5 3/6] target-m68k: use floatx80 internally |
Date: | Wed, 21 Jun 2017 09:37:19 -0700 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 |
On 06/21/2017 09:18 AM, Philippe Mathieu-Daudé wrote:
+typedef CPU_LDoubleU FPReg;What an awful name... Anyway checking on "qemu/bswap.h" it seems there is some endianess issue with it if your host is little-endian.
There is no endian-ness issue because we do not attempt to read that structure from memory as a whole. Instead, Laurent uses two big-endian loads (with appropriate address arithmetic) and stores the result into this host structure in host-endian order. Further, the host routines use the structure members by name and do not assume any particular relationship between them.
Do you have a way to run Berkeley TestFloat?
As noted in Laurent's cover message, floatx80 isn't quite right -- that is the x86 data type, and the proper m68k data type is slightly different.
I would expect the results from using floatx80 to be Just Good Enough to produce a working m68k user-land. It will produce correct results for normal numbers in arithmetic such as 1.0 + 10.0. But I would expect many of the edge conditions that TestFloat would attempt (especially de-normals and un-normals) would fail.
r~
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