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target/mips: Fix minor bug in FPU

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Wrong type of NaN was generated for IEEE 754-2008 by MADDF.<D|S> and
MSUBF.<D|S> instructions when the arguments were (Inf, Zero, NaN) or
(Zero, Inf, NaN).

The if-else statement establishes if the system conforms to IEEE
754-1985 or IEEE 754-2008, and defines different behaviors depending
on that. In case of IEEE 754-2008, in mentioned cases of inputs,
<MADDF|MSUBF>.<D|S> returns the input value 'c' [2] (page 53) and
raises floating point exception 'Invalid Operation' [1] (pages 349,
350).

These scenarios were tested and the results in QEMU emulation match
the results obtained on the machine that has a MIPS64R6 CPU.

[1] MIPS Architecture for Programmers Volume II-a: The MIPS64
    Instruction Set Reference Manual, Revision 6.06
[2] MIPS Architecture for Programmers Volume IV-j: The MIPS64
    SIMD Architecture Module, Revision 1.12

Signed-off-by: Mateja Marjanovic <mateja.marjanovic@rt-rk.com>
Message-Id: <1553008916-15274-2-git-send-email-mateja.marjanovic@rt-rk.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[AJB: fixed up commit message]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
This commit is contained in:
Mateja Marjanovic 2019-03-19 16:21:56 +01:00 committed by Alex Bennée
parent aec2927dda
commit 7ca96e1a9c
1 changed files with 16 additions and 8 deletions
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24
fpu/softfloat-specialize.h
View file

@ -495,15 +495,15 @@ static int pickNaNMulAdd(FloatClass a_cls, FloatClass b_cls, FloatClass c_cls,
return 1;
}
#elif defined(TARGET_MIPS)
/* For MIPS, the (inf,zero,qnan) case sets InvalidOp and returns
* the default NaN
*/
if (infzero) {
float_raise(float_flag_invalid, status);
return 3;
}
if (snan_bit_is_one(status)) {
/*
* For MIPS systems that conform to IEEE754-1985, the (inf,zero,nan)
* case sets InvalidOp and returns the default NaN
*/
if (infzero) {
float_raise(float_flag_invalid, status);
return 3;
}
/* Prefer sNaN over qNaN, in the a, b, c order. */
if (is_snan(a_cls)) {
return 0;
@ -519,6 +519,14 @@ static int pickNaNMulAdd(FloatClass a_cls, FloatClass b_cls, FloatClass c_cls,
return 2;
}
} else {
/*
* For MIPS systems that conform to IEEE754-2008, the (inf,zero,nan)
* case sets InvalidOp and returns the input value 'c'
*/
if (infzero) {
float_raise(float_flag_invalid, status);
return 2;
}
/* Prefer sNaN over qNaN, in the c, a, b order. */
if (is_snan(c_cls)) {
return 2;