On 28 March 2011 18:23, Alexander Graf <ag...@suse.de> wrote:
> On 03/24/2011 06:29 PM, Peter Maydell wrote:
>>> +/* condition codes for binary FP ops */
>>> +static uint32_t set_cc_f32(float32 v1, float32 v2)
>>> +{
>>> + if (float32_is_any_nan(v1) || float32_is_any_nan(v2)) {
>>> + return 3;
>>> + } else if (float32_eq(v1, v2,&env->fpu_status)) {
>>> + return 0;
>>> + } else if (float32_lt(v1, v2,&env->fpu_status)) {
>>> + return 1;
>>> + } else {
>>> + return 2;
>>> + }
>>> +}
>>
>> Can you not use float32_compare_quiet() (returns a value
>> telling you if it's less/equal/greater/unordered)?
>> If not, needs a comment saying why you need to do it the hard way.
>
> I just checked the macros there and it looks like float32_compare_quiet
> returns eq when both numbers are NaN.
Hmm?
if (( ( extractFloat ## s ## Exp( a ) == nan_exp ) && \
extractFloat ## s ## Frac( a ) ) || \
( ( extractFloat ## s ## Exp( b ) == nan_exp ) && \
extractFloat ## s ## Frac( b ) )) { \
if (!is_quiet || \
float ## s ## _is_signaling_nan( a ) || \
float ## s ## _is_signaling_nan( b ) ) { \
float_raise( float_flag_invalid STATUS_VAR); \
} \
return float_relation_unordered; \
} \
If A is a NaN (ie its exponent is nan_exp and the frac bits aren't zero)
or B is a NaN then we return float_relation_unordered.
> We would still have to convert from
> the return value from that over to a CC value. I honestly don't see any
> benefit - the code doesn't become cleaner or smaller.
So you get
static uint32_t set_cc_f32(float32 v1, float32 v2)
{
switch (float32_compare_quiet(v1, v2, &env->fpu_status)) {
case float_relation_unordered:
return 3;
case float_relation_equal:
return 0;
case float_relation_less:
return 1;
case float_relation_greater:
return 2;
case float_relation_unordered:
return 3;
}
}
(and you probably want to put the conversion switch into a function
since you'll be using it several times.)
Which I think is pretty straightforward, cleaner because we only
call one softfloat function rather than several, and should be
faster too (we get to avoid repeating a pile of tedious bit manipulation
in the eq and lt functions).
>>> +/* load 128-bit FP zero */
>>> +void HELPER(lzxr)(uint32_t f1)
>>> +{
>>> + CPU_QuadU x;
>>> + x.q = float64_to_float128(float64_zero,&env->fpu_status);
>>
>> Yuck. Just define a float128_zero if we need one.
>
> Good point. Mind to do so? I find myself struggling with the code there.
We could just follow the pattern of float128_default_nan_{low,high}
in softfloat.h:
#define float128_zero_low LIT64(0)
#define float128_zero_high LIT64(0)
then your function has:
x.q.high = float128_zero_high;
x.q.low = float128_zero_low;
Or we could do something with an expression that returns a
struct type; that would be cleaner. I think the default nan
code is assuming it might have to be compiled with something
other than gcc. However I forget the C syntax and have to go
home now :-)
-- PMM
