[FFmpeg-devel] [PATCH 6/6] truehd: add hand-scheduled ARM asm version of ff_mlp_pack_output.

[Clément Bœsch]

On Thu, Mar 20, 2014 at 03:30:21PM -0000, Ben Avison wrote:
> On Thu, 20 Mar 2014 09:41:59 -0000, Clément Bœsch <u at pkh.me> wrote:
> >>+.macro loadregoffsh2  group, index, base, offgroup, offindex
> >>+       .altmacro
> >>+       loadregoffsh2_ \group, %(\index), \base, \offgroup, %(\offindex)
> >>+       .noaltmacro
> >>+.endm
> >>+
> >>+.macro loadregoffsh2_ group, index, base, offgroup, offindex
> >>+        ldr     \group\index, [\base, \offgroup\offindex, lsl #2]
> >>+.endm
> >>+
> >>+.macro eorlslreg  check, data, group, index
> >>+        .altmacro
> >>+        eorlslreg_ \check, \data, \group, %(\index)
> >>+        .noaltmacro
> >>+.endm
> >>+
> >>+.macro eorlslreg_ check, data, group, index
> >>+        eor     \check, \check, \data, lsl \group\index
> >>+.endm
> >>+
> >
> >These 2 macros look like they are just 1 instruction each. They should be
> >inlined if possible, it's really unnecessary obfuscation.
> 
> I absolutely agree that it's horrible (I couldn't restrain myself from
> commenting on it myself next to the equivalent macros in mlpdsp_arm.S).
> However, that just seems to be the best that GAS can do - it has very
> poor expression manipulation abilities compared to other macro
> assemblers, and what little it can achieve is often by using deep nesting
> of macros like this.
> 
> What happens is that the outer macro is called with an assembler
> expression, which it evaluates to a string and passes to the inner macro.
> The inner macro performs a string concatenation with another argument and
> it is then able to interpret the resulting string as a symbolic register
> name.
> 
> The % operator only seems to be valid for invoking another macro - you
> don't seem to be able to combine it with a concatenation within a single
> level macro, using \group%(\index) or \group\()%(\index). Unless anyone
> knows any different? (The documentation for GAS leaves a lot to be
> desired in this area too.)
> 

JOIN() from libavutil/arm/asm.S can't help?

(sorry double mail in PV)

> Ben

-- 
Clément B.
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