Commit 7ca96e1a authored Mar 19, 2019 by Mateja Marjanovic Committed by Alex Bennée Mar 25, 2019

target/mips: Fix minor bug in FPU



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>

parent aec2927d

fpu/softfloat-specialize.h

+16 −8

Original line number	Diff line number	Diff line
		@@ -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 (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;
		}

		if (snan_bit_is_one(status)) {
		/* 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;