In commit 8adcff4ae7 ("fpu: handle raising Invalid for infzero in
pick_nan_muladd") we changed the handling of 0 * Inf + QNaN to always
raise the Invalid exception regardless of target architecture. (This
was a change affecting hppa, i386, sh4 and tricore.) However, this
was incorrect for i386, which documents in the SDM section 14.5.2
that for the 0 * Inf + NaN case that it will only raise the Invalid
exception when the input is an SNaN. (This is permitted by the IEEE
754-2008 specification, which documents that whether we raise Invalid
for 0 * Inf + QNaN is implementation defined.)
Adjust the softfloat pick_nan_muladd code to allow the target to
suppress the raising of Invalid for the inf * zero + NaN case (as an
extra flag orthogonal to its choice for when to use the default NaN),
and enable that for x86.
We do not revert here the behaviour change for hppa, sh4 or tricore:
* The sh4 manual is clear that it should signal Invalid
* The tricore manual is a bit vague but doesn't say it shouldn't
* The hppa manual doesn't talk about fused multiply-add corner
cases at all
Cc: qemu-stable@nongnu.org
Fixes: 8adcff4ae7 (""fpu: handle raising Invalid for infzero in
pick_nan_muladd")
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
include/fpu/softfloat-types.h | 16 +++++++++++++---
target/i386/tcg/fpu_helper.c | 5 ++++-
fpu/softfloat-parts.c.inc | 5 +++--
3 files changed, 20 insertions(+), 6 deletions(-)
diff --git a/include/fpu/softfloat-types.h b/include/fpu/softfloat-types.h
index 9d37cdfaa8e..c51b2a5b3de 100644
--- a/include/fpu/softfloat-types.h
+++ b/include/fpu/softfloat-types.h
@@ -278,11 +278,21 @@ typedef enum __attribute__((__packed__)) {
/* No propagation rule specified */
float_infzeronan_none = 0,
/* Result is never the default NaN (so always the input NaN) */
- float_infzeronan_dnan_never,
+ float_infzeronan_dnan_never = 1,
/* Result is always the default NaN */
- float_infzeronan_dnan_always,
+ float_infzeronan_dnan_always = 2,
/* Result is the default NaN if the input NaN is quiet */
- float_infzeronan_dnan_if_qnan,
+ float_infzeronan_dnan_if_qnan = 3,
+ /*
+ * Don't raise Invalid for 0 * Inf + NaN. Default is to raise.
+ * IEEE 754-2008 section 7.2 makes it implementation defined whether
+ * 0 * Inf + QNaN raises Invalid or not. Note that 0 * Inf + SNaN will
+ * raise the Invalid flag for the SNaN anyway.
+ *
+ * This is a flag which can be ORed in with any of the above
+ * DNaN behaviour options.
+ */
+ float_infzeronan_suppress_invalid = (1 << 7),