Re: [Qemu-devel] [PATCH RFC v19 09/13] target-avr: adding instruction decoder

[Michael Rolnik <mrolnik@gmail.com>]

this is generated code.

On Tue, Jun 13, 2017 at 11:01 PM, Thomas Huth <huth@tuxfamily.org> wrote:

> On 08.06.2017 20:49, Michael Rolnik wrote:
> > Signed-off-by: Michael Rolnik <mrolnik@gmail.com>
> > Message-Id: <1471522070-77598-10-git-send-email-mrolnik@gmail.com>
> > Signed-off-by: Richard Henderson <rth@twiddle.net>
> > ---
> >  target/avr/Makefile.objs |   1 +
> >  target/avr/decode.c      | 691 ++++++++++++++++++++++++++++++
> +++++++++++++++++
> >  target/avr/translate.c   |   2 +
> >  3 files changed, 694 insertions(+)
> >  create mode 100644 target/avr/decode.c
> >
> > diff --git a/target/avr/Makefile.objs b/target/avr/Makefile.objs
> > index a448792ff3..9848b1cb4c 100644
> > --- a/target/avr/Makefile.objs
> > +++ b/target/avr/Makefile.objs
> > @@ -21,4 +21,5 @@
> >  obj-y += translate.o cpu.o helper.o
> >  obj-y += gdbstub.o
> >  obj-y += translate-inst.o
> > +obj-y += decode.o
> >  obj-$(CONFIG_SOFTMMU) += machine.o
> > diff --git a/target/avr/decode.c b/target/avr/decode.c
> > new file mode 100644
> > index 0000000000..2d2e54e448
> > --- /dev/null
> > +++ b/target/avr/decode.c
> > @@ -0,0 +1,691 @@
> > +/*
> > + * QEMU AVR CPU
> > + *
> > + * Copyright (c) 2016 Michael Rolnik
> > + *
> > + * This library is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU Lesser General Public
> > + * License as published by the Free Software Foundation; either
> > + * version 2.1 of the License, or (at your option) any later version.
> > + *
> > + * This library is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > + * Lesser General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU Lesser General Public
> > + * License along with this library; if not, see
> > + * <http://www.gnu.org/licenses/lgpl-2.1.html>
> > + */
> > +
> > +#include <stdint.h>
> > +#include "translate.h"
> > +
> > +void avr_decode(uint32_t pc, uint32_t *l, uint32_t c,
> translate_function_t *t)
> > +{
> > +    uint32_t opc = extract32(c, 0, 16);
> > +    switch (opc & 0x0000d000) {
> > +        case 0x00000000: {
> > +            switch (opc & 0x00002c00) {
> > +                case 0x00000000: {
> > +                    switch (opc & 0x00000300) {
> > +                        case 0x00000000: {
> > +                            *l = 16;
> > +                            *t = &avr_translate_NOP;
> > +                            break;
> > +                        }
> > +                        case 0x00000100: {
> > +                            *l = 16;
> > +                            *t = &avr_translate_MOVW;
> > +                            break;
> > +                        }
> > +                        case 0x00000200: {
> > +                            *l = 16;
> > +                            *t = &avr_translate_MULS;
> > +                            break;
> > +                        }
> > +                        case 0x00000300: {
> > +                            switch (opc & 0x00000088) {
> > +                                case 0x00000000: {
> > +                                    *l = 16;
> > +                                    *t = &avr_translate_MULSU;
> > +                                    break;
> > +                                }
> > +                                case 0x00000008: {
> > +                                    *l = 16;
> > +                                    *t = &avr_translate_FMUL;
> > +                                    break;
> > +                                }
> > +                                case 0x00000080: {
> > +                                    *l = 16;
> > +                                    *t = &avr_translate_FMULS;
> > +                                    break;
> > +                                }
> > +                                case 0x00000088: {
> > +                                    *l = 16;
> > +                                    *t = &avr_translate_FMULSU;
> > +                                    break;
> > +                                }
> > +                            }
> > +                            break;
> > +                        }
> > +                    }
> > +                    break;
> > +                }
> [...]
>
> This functions with all those nested switch-statements is really huge
> and hard to read. Could you split it up in multiple functions or use
> tables instead?
>
> Also coding style is not very space-saving here ... you don't need most
> of the curly braces, and it is more common nowadays to put the "case" on
> the same indentation level as the "switch" keyword.
>
>  Thomas
>



-- 
Best Regards,
Michael Rolnik