On Wed, Jul 16, 2014 at 11:04:22PM +0100, Zi Shen Lim wrote:
> On Wed, Jul 16, 2014 at 05:17:15PM +0100, Will Deacon wrote:
> > On Tue, Jul 15, 2014 at 07:25:06AM +0100, Zi Shen Lim wrote:
> > > Introduce function to generate move wide (immediate) instructions.
> >
> > [...]
> >
> > > +u32 aarch64_insn_gen_movewide(enum aarch64_insn_register dst,
> > > + int imm, int shift,
> > > + enum aarch64_insn_variant variant,
> > > + enum aarch64_insn_movewide_type type)
> > > +{
> > > + u32 insn;
> > > +
> > > + switch (type) {
> > > + case AARCH64_INSN_MOVEWIDE_ZERO:
> > > + insn = aarch64_insn_get_movz_value();
> > > + break;
> > > + case AARCH64_INSN_MOVEWIDE_KEEP:
> > > + insn = aarch64_insn_get_movk_value();
> > > + break;
> > > + case AARCH64_INSN_MOVEWIDE_INVERSE:
> > > + insn = aarch64_insn_get_movn_value();
> > > + break;
> > > + default:
> > > + BUG_ON(1);
> > > + }
> > > +
> > > + BUG_ON(imm < 0 || imm > 65535);
> >
> > Do this check with masking instead?
>
> Ok, if you prefer, I can change it to:
>
> BUG_ON(imm & ~GENMASK(15, 0));
Sure, that or use a named constant for the upper-bound (SZ_64K - 1).
> > > + switch (variant) {
> > > + case AARCH64_INSN_VARIANT_32BIT:
> > > + BUG_ON(shift != 0 && shift != 16);
> > > + break;
> > > + case AARCH64_INSN_VARIANT_64BIT:
> > > + insn |= BIT(31);
> > > + BUG_ON(shift != 0 && shift != 16 && shift != 32 &&
> > > + shift != 48);
> >
> > Would be neater as a nested switch, perhaps? If you reorder the
> > outer-switch, you could probably fall-through too and combine the shift
> > checks.
>
> Not sure I picture what you had in mind... I couldn't come up with a
> neater version with the properties you described.
>
> The alternative I had was using masks instead of integer values, but
> one could argue that while neater, it could also be harder to read:
>
> switch (variant) {
> case AARCH64_INSN_VARIANT_32BIT:
> BUG_ON(shift & ~BIT(4));
> break;
> case AARCH64_INSN_VARIANT_64BIT:
> insn |= BIT(31);
> BUG_ON(shift & ~GENMASK(5, 4));
> ...
I was thinking of using nested switches, but that doesn't fall out like I
hoped. How about:
switch (variant) {
case AARCH64_INSN_VARIANT_64BIT:
BUG_ON(shift != 32 && shift != 48);
case AARCH64_INSN_VARIANT_32BIT:
BUG_ON(shift != 0 && shift != 16);
};
?
Will
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