MIPS: math-emu: Add IEEE Std 754-2008 NaN encoding emulation
Implement IEEE Std 754-2008 NaN encoding wired to the state of the
FCSR.NAN2008 bit. Make the interpretation of the quiet bit in NaN data
as follows:
* in the legacy mode originally defined by the MIPS architecture the
value of 1 denotes an sNaN whereas the value of 0 denotes a qNaN,
* in the 2008 mode introduced with revision 5 of the MIPS architecture
the value of 0 denotes an sNaN whereas the value of 1 denotes a qNaN,
following the definition of the preferred NaN encoding introduced with
IEEE Std 754-2008.
In the 2008 mode, following the requirement of the said standard, quiet
an sNaN where needed by setting the quiet bit to 1 and leaving all the
NaN payload bits unchanged.
Update format conversion operations according to the rules set by IEEE
Std 754-2008 and the MIPS architecture. Specifically:
* propagate NaN payload bits through conversions between floating-point
formats such that as much information as possible is preserved and
specifically a conversion from a narrower format to a wider format and
then back to the original format does not change a qNaN payload in any
way,
* conversions from a floating-point to an integer format where the
source is a NaN, infinity or a value that would convert to an integer
outside the range of the result format produce, under the default
exception handling, the respective values defined by the MIPS
architecture.
In full FPU emulation set the FIR.HAS2008 bit to 1, however do not make
any further FCSR bits writable.
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/11477/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/math-emu/sp_tlong.c b/arch/mips/math-emu/sp_tlong.c
index 9f3c742..a2450c7 100644
--- a/arch/mips/math-emu/sp_tlong.c
+++ b/arch/mips/math-emu/sp_tlong.c
@@ -39,10 +39,13 @@
switch (xc) {
case IEEE754_CLASS_SNAN:
case IEEE754_CLASS_QNAN:
- case IEEE754_CLASS_INF:
ieee754_setcx(IEEE754_INVALID_OPERATION);
return ieee754di_indef();
+ case IEEE754_CLASS_INF:
+ ieee754_setcx(IEEE754_INVALID_OPERATION);
+ return ieee754di_overflow(xs);
+
case IEEE754_CLASS_ZERO:
return 0;
@@ -57,7 +60,7 @@
/* Set invalid. We will only use overflow for floating
point overflow */
ieee754_setcx(IEEE754_INVALID_OPERATION);
- return ieee754di_indef();
+ return ieee754di_overflow(xs);
}
/* oh gawd */
if (xe > SP_FBITS) {
@@ -94,7 +97,7 @@
if ((xm >> 63) != 0) {
/* This can happen after rounding */
ieee754_setcx(IEEE754_INVALID_OPERATION);
- return ieee754di_indef();
+ return ieee754di_overflow(xs);
}
if (round || sticky)
ieee754_setcx(IEEE754_INEXACT);
