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[Bug 1923629] Re: RISC-V Vector Instruction vssub.vv not saturating
From: |
Alistair Francis |
Subject: |
[Bug 1923629] Re: RISC-V Vector Instruction vssub.vv not saturating |
Date: |
Thu, 15 Apr 2021 04:42:15 -0000 |
Thanks for raising this bug case. A fix should be available soon.
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https://bugs.launchpad.net/bugs/1923629
Title:
RISC-V Vector Instruction vssub.vv not saturating
Status in QEMU:
New
Bug description:
I noticed doing a negate ( 0 – 0x80000000 ) using vssub.vv produces an
incorrect result of 0x80000000 (should saturate to 0x7FFFFFFF).
Here is the bit of the code:
vmv.v.i v16, 0
…
8f040457 vssub.vv v8,v16,v8
I believe the instruction encoding is correct (vssub.vv with vd = v8,
vs2 = v16, rs1 = v8), but the result does not saturate in QEMU.
I’ve just tested with what I think is the latest branch (
https://github.com/sifive/qemu/tree/rvv-1.0-upstream-v7 commit 26 Feb
2021: 1151361fa7d45cc90d69086ccf1a4d8397931811 ) and the problem still
exists.
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