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[Qemu-devel] Re: [PATCH] softfloat: fix floatx80_is_{quiet, signaling}_n


From: Peter Maydell
Subject: [Qemu-devel] Re: [PATCH] softfloat: fix floatx80_is_{quiet, signaling}_nan()
Date: Wed, 12 Jan 2011 15:05:10 -0600

On 12 January 2011 13:59, Aurelien Jarno <address@hidden> wrote:

> @@ -494,7 +495,8 @@ int floatx80_is_quiet_nan( floatx80 a )
>  int floatx80_is_signaling_nan( floatx80 a )
>  {
>  #if SNAN_BIT_IS_ONE
> -    return ( ( a.high & 0x7FFF ) == 0x7FFF ) && (bits64) ( a.low<<1 );
> +    return ( ( a.high & 0x7FFF ) == 0x7FFF )
> +        && (LIT64( 0x8000000000000000 ) >= ((bits64) ( a.low<<1 )));
>  #else
>     bits64 aLow;

If a is {0x7ffff,0} (ie +inf) this will return true, which is wrong.
Do you want "<=" instead?

Actually, will
  return ((a.high & 0x7fff) == 0x7fff) && (a.low >= LIT64(0x4000000000000000));
do? Untested but I think it will do the right thing. I'm not sure
why this code has those bit64 casts, incidentally, since a.low is
already a uint64_t.

Also, maybe we should have a comment somewhere explaining
why this is different from the other NaN functions (ie that the
x80 format has an explicit bit and the others don't) ?

-- PMM



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