MIPS: math-emu: Always propagate sNaN payload in quieting
Propagate sNaN payload in quieting in the legacy-NaN mode as well. If
clearing the quiet bit would produce infinity, then set the next lower
trailing significand field bit, matching the SB-1 and BMIPS5000 hardware
implementations. Some other MIPS FPU hardware implementations do
produce the default qNaN bit pattern instead.
This reverts some changes made for semantics preservation with commit
dc3ddf42 [MIPS: math-emu: Update sNaN quieting handlers], consequently
bringing back most of the semantics from before commit fdffbafb [Lots of
FPU bug fixes from Kjeld Borch Egevang.], except from the qNaN produced
in the infinity case. Previously the default qNaN bit pattern was
produced in that case.
Signed-off-by: Maciej W. Rozycki <macro@imgtec.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Fortune <Matthew.Fortune@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/11483/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/math-emu/ieee754dp.c b/arch/mips/math-emu/ieee754dp.c
index 47d26c8..465a034 100644
--- a/arch/mips/math-emu/ieee754dp.c
+++ b/arch/mips/math-emu/ieee754dp.c
@@ -54,10 +54,13 @@
assert(ieee754dp_issnan(r));
ieee754_setcx(IEEE754_INVALID_OPERATION);
- if (ieee754_csr.nan2008)
+ if (ieee754_csr.nan2008) {
DPMANT(r) |= DP_MBIT(DP_FBITS - 1);
- else
- r = ieee754dp_indef();
+ } else {
+ DPMANT(r) &= ~DP_MBIT(DP_FBITS - 1);
+ if (!ieee754dp_isnan(r))
+ DPMANT(r) |= DP_MBIT(DP_FBITS - 2);
+ }
return r;
}