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Subject: Re: [boost] Any interest in bitstream class?
From: Paul Long (plong_at_[hidden])
Date: 2013-06-29 22:28:22

On 6/29/2013 9:48 AM, Phil Endecott wrote:
> Have you measured the performance of your implementation ... ?

No, I have not measured the performance of ibitstream.

> I'm curious to know if you are doing bit-by-bit processing of the fields
> with shift amounts known only at run time, compared to extracting
> groups of
> contiguous bits simultaneously with shift amounts known at compile time -
> and if so, how much that affects performance.

ibitstream performs bit-by-bit processing. It can be optimized to a
certain degree as a follow-on task. I suppose that by exposing some
bitstream code to the calling context via inlining, the compiler could
perform some optimizations, e.g., strength reduction, but I haven't
thought about it.

> I have previously tried to do some basic MPEG stream processing on an
> embedded device and started trying to write a general-purpose facility
> like yours, but decided that it was not fast enough.

Hmm... I guess I have been thinking that bitstream would be used for
something less intensive and more high level like packetization as
opposed to being the sole means of a writing and reading bits for a
media codec. I believe the performance--once optimized--can be quite
good and often good enough, but it will never be as efficient as
hand-coded logic.


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