On Fri, Feb 03, 2017 at 02:40:09PM +0000, Peter Maydell wrote:
> On 1 February 2017 at 10:49, Bharata B Rao <bhar...@linux.vnet.ibm.com> wrote:
> > Implement float128_to_uint64() and use that to implement
> > float128_to_uint64_round_to_zero()
> >
> > This is required by xscvqpudz instruction of PowerPC ISA 3.0.
> >
> > Signed-off-by: Bharata B Rao <bhar...@linux.vnet.ibm.com>
> > ---
> > fpu/softfloat.c | 65
> > +++++++++++++++++++++++++++++++++++++++++++++++++
> > include/fpu/softfloat.h | 2 ++
> > 2 files changed, 67 insertions(+)
> >
> > diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> > index c295f31..49a06c5 100644
> > --- a/fpu/softfloat.c
> > +++ b/fpu/softfloat.c
> > @@ -6110,6 +6110,71 @@ int64_t float128_to_int64_round_to_zero(float128 a,
> > float_status *status)
> >
> >
> > /*----------------------------------------------------------------------------
> > | Returns the result of converting the quadruple-precision floating-point
> > +| value `a' to the 64-bit unsigned integer format. The conversion
> > +| is performed according to the IEC/IEEE Standard for Binary Floating-Point
> > +| Arithmetic---which means in particular that the conversion is rounded
> > +| according to the current rounding mode. If `a' is a NaN, the largest
> > +| positive integer is returned. Otherwise, if the conversion overflows,
> > the
> > +| largest unsigned integer is returned. If 'a' is negative, the value is
> > +| rounded and zero is returned; negative values that do not round to zero
> > +| will raise the inexact exception.
> > +*----------------------------------------------------------------------------*/
> > +
> > +uint64_t float128_to_uint64(float128 a, float_status *status)
> > +{
> > + flag aSign;
> > + int32_t aExp, shiftCount;
> > + uint64_t aSig0, aSig1;
>
> I think we should have a float128_squash_input_denormal() function
> which we call here (compare float64_to_uint64).
I followed float128_to_int64() which doesn't have that _denormal() call.
>
> > +
> > + aSig1 = extractFloat128Frac1( a );
>
> Can you use the QEMU coding style for this rather than following
> the softfloat weird one, please?
Sure, I will henceforth switch to QEMU coding style, I was under the
impression that we should stick to the existing style since almost
entire softfloat.c is in different style.
>
> > + aSig0 = extractFloat128Frac0( a );
> > + aExp = extractFloat128Exp( a );
> > + aSign = extractFloat128Sign( a );
> > + if ( aExp ) aSig0 |= LIT64( 0x0001000000000000 );
> > + shiftCount = 0x402F - aExp;
> > + if ( shiftCount <= 0 ) {
> > + if ( 0x403E < aExp ) {
> > + float_raise(float_flag_invalid, status);
> > + if ( ! aSign
> > + || ( ( aExp == 0x7FFF )
> > + && ( aSig1 || ( aSig0 != LIT64( 0x0001000000000000 )
> > ) )
> > + )
> > + ) {
> > + return LIT64( 0xFFFFFFFFFFFFFFFF );
> > + }
> > + return 0;
> > + }
> > + shortShift128Left( aSig0, aSig1, - shiftCount, &aSig0, &aSig1 );
> > + }
> > + else {
> > + shift64ExtraRightJamming( aSig0, aSig1, shiftCount, &aSig0, &aSig1
> > );
> > + }
> > + return roundAndPackUint64(aSign, aSig0, aSig1, status);
>
> I'm finding this a bit difficult to understand, because it doesn't
> follow the code pattern of (for instance) float64_to_uint64().
> Is it based on some other existing function?
As I said above, it is based on float128_to_int64()
Actually what I really need is float128_to_uint64_round_to_zero().
However it is a bit confusing as to which existing routine to follow here.
I see there are 3 different ways floatXX_to_uintYY_round_to_zero is done:
1. Eg float64_to_uint32_round_to_zero()
Uses float64_to_uint64_round_to_zero()
2. Eg float128_to_int32_round_to_zero()
Doesn't use float128_to_int32() but instead is implemented
fully separately.
3. Eg float64_to_uint64_round_to_zero()
Sets the rounding mode to round-to-zero
Uses float64_to_uint64()
I don't know if the above variants came about during different points
in time or they are actually implemented that way due to some
subtlety involved. I am following the 3rd pattern above as
I found it to be easier for this particular case (float128_to_uint128)
In fact I need float128_to_uint32() also next, but haven't yet been
able to figure out which way to do it.
>
> > +}
> > +
> > +/*----------------------------------------------------------------------------
> > +| Returns the result of converting the quadruple-precision floating-point
> > +| value `a' to the 64-bit unsigned integer format. The conversion
> > +| is performed according to the IEC/IEEE Standard for Binary Floating-Point
> > +| Arithmetic, except that the conversion is always rounded toward zero.
> > +| according to the current rounding mode. If `a' is a NaN, the largest
> > +| positive integer is returned. Otherwise, if the conversion overflows,
> > the
> > +| largest unsigned integer is returned. If 'a' is negative, the value is
> > +| rounded and zero is returned; negative values that do not round to zero
> > +| will raise the inexact exception.
> > +*----------------------------------------------------------------------------*/
> > +
> > +uint64_t float128_to_uint64_round_to_zero(float128 a, float_status *status)
> > +{
> > + signed char current_rounding_mode = status->float_rounding_mode;
> > + set_float_rounding_mode(float_round_to_zero, status);
> > + uint64_t v = float128_to_uint64(a, status);
> > + set_float_rounding_mode(current_rounding_mode, status);
> > + return v;
> > +}
>
> This function is OK, though our coding style would suggest putting
> the declaration of 'uint64_t v;' at the top of the function.
Sure will change in the next iteration when I switch to QEMU style.
Regards,
Bharata.
