Re: [Qemu-devel] [PATCH 1/7] softfloat: Fix sNaN handling in FP conversion operations

[Leon Alrae]

On 09/12/2014 01:54, Maciej W. Rozycki wrote:
> Fix sNaN handling in floating-point format conversion operations, that 
> are classified by the IEEE 754-2008 standard as general-computational 
> operations [1]:
> 
> "5.4 formatOf general-computational operations
> 
> "5.4.2 Conversion operations for floating-point formats and decimal 
> character sequences
> 
> "Implementations shall provide the following formatOf conversion 
> operations from all supported floating-point formats to all supported 
> floating-point formats, as well as conversions to and from decimal 
> character sequences.  These operations shall not propagate non-canonical 
> results.  Some format conversion operations produce results in a 
> different radix than the operands."
> 
> according to the quietening requirement [2] set by the same standard:
> 
> "7.2 Invalid operation
> 
> "For operations producing results in floating-point format, the default 
> result of an operation that signals the invalid operation exception 
> shall be a quiet NaN that should provide some diagnostic information 
> (see 6.2).
> 
> "These operations are:
>     a)   any general-computational or signaling-computational operation 
>          on a signaling NaN (see 6.2), except for some conversions (see 
>          5.12)"
> 
> and the reference above is [3]:
> 
> "5.12 Details of conversion between floating-point data and external 
> character sequences"
> 
> so does not apply to conversions a pair of floating-point formats.
> 
> Therefore quieten any sNaN encountered in floating-point format 
> conversions, in the usual manner.
> 
> References:
> 
> [1] "IEEE Standard for Floating-Point Arithmetic", IEEE Computer 
>     Society, IEEE Std 754-2008, 29 August 2008, pp. 21-22
> 
> [2] same, p. 37
> 
> [3] same, p. 30
> 
> Signed-off-by: Maciej W. Rozycki <address@hidden>
> ---
>  This is in particular how MIPS hardware operates, other processors 
> supposedly do the same if they claim compliance to IEEE 754.
> 
>  Please apply.
> 
> qemu-softfloat-convert-snan.diff
> Index: qemu-git-trunk/fpu/softfloat.c

Reviewed-by: Leon Alrae <address@hidden>