Messages in this thread | | | Date | Thu, 17 Jul 2014 10:41:02 +0100 | From | Will Deacon <> | Subject | Re: [PATCH RFCv3 08/14] arm64: introduce aarch64_insn_gen_movewide() |
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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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