[Flac-dev] libFLAC bitbuffer optimizations

[Josh Coalson]

thanks for the patch.

also, if you have miroslav's patch again a more updated version
of bitbuffer.c that would be great.  I have been meaning to get
around to applying it for a long time.

btw how are you playing it on the ipod?

not sure how to help out with lpc_restore_signal().  there are
x86 and PPC versions of the routines in CVS that might be good
references.  it is basically a multiply-accumulate loop but you
have to be careful about overflow.  an ARM7 version of this
function would help the speed on several other FLAC-supported
devices.

Josh

--- Eric Wong <eric at petta-tech.com> wrote:

> Pulled from my Arch archive, this following patch seems to have made
> quite a difference in getting my ARM7TDMI chip to play FLAC
> (compression
> levels 0-2) on my ipod.  I don't have benchmarks with hard numbers,
> but
> playing with skips vs playing without skips is a fairly noticeable
> difference.
> 
> memcpy and memset on uClibc are optimized in asm for the ARM7TDMI in
> uClibc. Other hardware/libc combinations may not benefit as much, but
> most C libraries should have optimized versions of these functions.
> 
> I'm also using Miroslav Lichvar's patch from Jan/Feb 2003 (that was
> posted here), which I retrieved and hand-merged from the archives.  I
> made a few minor changes to that, too, and managed to reduce it by a
> few
> ops (nothing major).  I can repost both his patch and mine on top of
> it,
> too.
> 
> I also have some alternate lpc_restore_signal implementations (in C)
> I
> can extract and post (don't really have a clean changeset), but I
> haven't been able to get lpc-enabled FLACs to play at normal speeds,
> yet.  I'll try to find some time in the next few months and learn
> enough
> asm tricks to make this one faster for the ARM.  Help would be
> greatly
> appreciated.  Right now I'm just looking at compiler output in asm,
> and
> counting ops (especially branch calls).
> 
> Anyways, here goes the patch I described in my first paragraph:
> 
> * added files
> 
>    
>
{arch}/flac/flac--ipod/flac--ipod--1.1.0/eric at petta-tech.com--2004b-ordinary/patch-log/patch-27
> 
> * modified files
> 
> --- orig/src/libFLAC/bitbuffer.c
> +++ mod/src/libFLAC/bitbuffer.c
> @@ -233,11 +233,26 @@
>  
>  	/* first shift the unconsumed buffer data toward the front as much
> as possible */
>  	if(bb->total_consumed_bits >= FLAC__BITS_PER_BLURB) {
> +#if FLAC__BITS_PER_BLURB == 8
> +		/*
> +		 * memset and memcpy are usually implemented in assembly language
> +		 * by the system libc, and they can be much faster
> +		 */
> +		unsigned r_end = (bb->blurbs + (bb->bits? 1:0)),
> +		         r = bb->consumed_blurbs, l = r_end - r;
> +		FLAC__blurb * rbuffer = &bb->buffer[r];
> +		memcpy(&bb->buffer[0], rbuffer, r_end/4 + r_end%4);
> +		memset(++rbuffer, 0, l/4 + l%4);
> +#elif FLAC__BITS_PER_BLURB == 32
> +		/* the original version */
>  		unsigned l = 0, r = bb->consumed_blurbs, r_end = bb->blurbs +
> (bb->bits? 1:0);
>  		for( ; r < r_end; l++, r++)
>  			bb->buffer[l] = bb->buffer[r];
>  		for( ; l < r_end; l++)
>  			bb->buffer[l] = 0;
> +#else
> +	FLAC__ASSERT(false); /* ERROR, only sizes of 8 and 32 are supported
> */
> +#endif /* FLAC__BITS_PER_BLURB == 32 or 8 */
>  		bb->blurbs -= bb->consumed_blurbs;
>  		bb->total_bits -= FLAC__BLURBS_TO_BITS(bb->consumed_blurbs);
>  		bb->consumed_blurbs = 0;
> 
> 
> 
> -- 
> Eric Wong / normalperson on freenode



		
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