On Wed, 4 May 2016, Aleksandar Markovic wrote:
> > > @@ -8919,7 +8920,11 @@ static void gen_farith (DisasContext *ctx, enum
> > > fopcode op1,
> > > TCGv_i64 fp64 = tcg_temp_new_i64();
> > >
> > > gen_load_fpr32(ctx, fp32, fs);
> > > - gen_helper_float_roundl_s(fp64, cpu_env, fp32);
> > > + if ((ctx->insn_flags & ISA_MIPS32R6) && (ctx->nan2008)) {
>
> > Why testing the version of the architecture? This will generate wrong
> > helper for P5600 which is R5 and IEEE 754-2008 compliant.
>
> The code reflects the documentation.
>
> I just want to bring to your attention following two versions of the
> paragraph detailing return value of ROUND.L.S for some special cases - one
> version from R6 documention, and the other from R5 documentation:
>
> R6: ("MIPS® Architecture For Programmers Volume II-A: The MIPS64® Instruction
> Set Reference Manual", Revision 6.04, page 393)
>
> "When the source value is Infinity, NaN, or rounds to an integer outside the
> range -2 63 to 2 63 -1, the result cannot be
> represented correctly and an IEEE Invalid Operation condition exists. The
> Invalid Operation flag is set in the FCSR.
> If the Invalid Operation Enable bit is set in the FCSR, no result is written
> to fd and an Invalid Operation exception is
> taken immediately. Otherwise, a default result is written to fd. On cores
> with FCSR[NAN2008]=0, the default result is
> 2^63–1. On cores with FCSR[NAN2008]=1, the default result is:
> • 0 when the input value is NaN
> • 2^63 –1 when the input value is +infinity or rounds to a number larger
> than 2^63 –1
> • -2^63 –1 when the input value is –infinity or rounds to a number smaller
> than -2^63 –1"
This is clearly wrong given that FCSR[NAN2008] is hardwired to 1 in R6;
see Table 6.8 in MIPS64 vol. I rev. 6.01. Please note that individual
instruction descriptions should not be used as a (primary) reference,
especially in the case of documentation discrepancies -- refer to Table
6.3 in vol. I for architectural definitions.
> R5: ("MIPS® Architecture For Programmers Volume II-A: The MIPS64® Instruction
> Set Reference Manual", Revision 5.04, page 314)
>
> "When the source value is Infinity, NaN, or rounds to an integer outside the
> range -2 63 to 2 63 -1, the result cannot be
> represented correctly and an IEEE Invalid Operation condition exists. In this
> case the Invalid Operation flag is set in
> the FCSR. If the Invalid Operation Enable bit is set in the FCSR, no result
> is written to fd and an Invalid Operation
> exception is taken immediately. Otherwise, the default result, 2 63 – 1, is
> written to fd."
This is likewise wrong, and refer to Table 5.7 and 5.3 respectively in
MIPS64 vol. I rev. 5.04.
In any case FCSR[NAN2008] is the only condition to be referred.
Maciej
