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From: Leon Alrae <leon.alrae@imgtec.com>
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Date: Fri, 1 Apr 2016 20:02:41 +0100
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Subject: Re: [Qemu-devel] [PATCH 1/2] softfloat: Enable
 run-time-configurable meaning of signaling NaN bit
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To: Aleksandar Markovic <aleksandar.markovic@rt-rk.com>, qemu-devel@nongnu.org
Cc: peter.maydell@linaro.org, ehabkost@redhat.com, proljc@gmail.com, mark.cave-ayland@ilande.co.uk, agraf@suse.de, kbastian@mail.uni-paderborn.de, petar.jovanovic@imgtec.com, blauwirbel@gmail.com, jcmvbkbc@gmail.com, miodrag.dinic@imgtec.com, qemu-arm@nongnu.org, qemu-ppc@nongnu.org, edgar.iglesias@gmail.com, pbonzini@redhat.com, gxt@mprc.pku.edu.cn, afaerber@suse.de, aurelien@aurel32.net, rth@twiddle.net

On 25/03/16 12:50, Aleksandar Markovic wrote:
>  /*----------------------------------------------------------------------------
>  | The pattern for a default generated single-precision NaN.
>  *----------------------------------------------------------------------------*/
> +float32 float32_default_nan(float_status *status) {
>  #if defined(TARGET_SPARC)
> -const float32 float32_default_nan = const_float32(0x7FFFFFFF);
> +    return const_float32(0x7FFFFFFF);
>  #elif defined(TARGET_PPC) || defined(TARGET_ARM) || defined(TARGET_ALPHA) || \
>        defined(TARGET_XTENSA) || defined(TARGET_S390X) || defined(TARGET_TRICORE)
> -const float32 float32_default_nan = const_float32(0x7FC00000);
> -#elif SNAN_BIT_IS_ONE
> -const float32 float32_default_nan = const_float32(0x7FBFFFFF);
> +    return const_float32(0x7FC00000);
>  #else
> -const float32 float32_default_nan = const_float32(0xFFC00000);
> +    if (status->snan_bit_is_one)
> +        return const_float32(0x7FBFFFFF);
> +    else
> +        return const_float32(0xFFC00000);

Here for MIPS (when FCR31.NAN2008 is set) we should generate 0x7FC00000
for single-precision. Reference:
"MIPS Architecture For Programmers, Volume I-A: Introduction to the
MIPS64 Architecture", Imagination Technologies LTD., Document Number:
MD00083, Revision 6.01, August 20, 2014, Table 6.3 "Value Supplied When
a New Quiet NaN Is Created", p. 84

Also, for double-precision we should generate 0x7FF8000000000000.

Thanks,
Leon