Re: [PATCH v2 04/28] softfloat: Move minmax_flags to softfloat-parts.c.inc

[Richard Henderson]

On 6/2/21 1:36 PM, Alex Bennée wrote:
> Richard Henderson <richard.henderson@linaro.org> writes:
>
> > Rename to parts$N_minmax.  Combine 3 bool arguments to a bitmask,
> > return a tri-state value to indicate nan vs unchanged operand.
> > Introduce ftype_minmax functions as a common optimization point.
> > Fold bfloat16 expansions into the same macro as the other types.
> >
> > Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> > ---
> <snip>
> > -        switch (a.cls) {
> > -        case float_class_normal:
> > -            a_exp = a.exp;
> > -            break;
> > -        case float_class_inf:
> > -            a_exp = INT_MAX;
> > -            break;
> > -        case float_class_zero:
> > -            a_exp = INT_MIN;
> > -            break;
> > -        default:
> > -            g_assert_not_reached();
> > -            break;
> > -        }
> > -        switch (b.cls) {
> > -        case float_class_normal:
> > -            b_exp = b.exp;
> > -            break;
> > -        case float_class_inf:
> > -            b_exp = INT_MAX;
> > -            break;
> > -        case float_class_zero:
> > -            b_exp = INT_MIN;
> > -            break;
> > -        default:
> > -            g_assert_not_reached();
> > -            break;
> > -        }
> > -
> <snip>
> > +    if (unlikely(ab_mask != float_cmask_normal)) {
> > +        switch (a->cls) {
> > +        case float_class_normal:
> > +            break;
> > +        case float_class_inf:
> > +            a_exp = INT16_MAX;
>
> We've gone from min/max of our internal representation to INT16_MIN/MAX
> - I guess that doesn't break until we get to Float256 but why the change?

Ah, because I've changed from "bool a_less" to "int cmp".  I subtract the two 
exponents and I don't want that subtraction to overflow.


r~