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Library: Reverse-engineered ALAC decoder v0.1.0
Imported: 2005-08-14 by Dave Chapman
This directory contains a local version of an ALAC (Apple Lossless Audio
Codec) for use by Rockbox for software decoding of ALAC files. It is
based on the reverse-engineered decoder by David Hamilton.
LICENSING INFORMATION
/*
* ALAC (Apple Lossless Audio Codec) decoder
* Copyright (c) 2005 David Hammerton
* All rights reserved.
*
* This is the actual decoder.
*
* http://crazney.net/programs/itunes/alac.html
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use,
* copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*
*/
IMPORT DETAILS
The base version first imported into Rockbox was the first release
(v0.1.0) of the ALAC decoder by David Hammerton.
Only the files alac.[ch], demux.[ch] and stream.h were used.
stream.c (the original FILE* based I/O implementation) was replaced with
functions in the ALAC codec - to interface with the Rockbox audio playback
system.
References to <stdint.h> were replaced with <inttypes.h> and debugging
calls to fprintf were removed.
The ALAC decoder itself was modified to return samples in host-endian
order, instead of little-endian.
The run-time detection of CPU endianness was replaced with
compile-time tests of the ROCKBOX_LITTLE_ENDIAN define.
All malloc calls were removed from alac.c, but some are still present
in the metadata parser in demux.c - to store unbounded data such as
the size in bytes of each compressed block in the file.
The only changes to demux.c were to remove debugging calls to fprintf.
The most-used buffers (the temporary 32-bit output buffer) were moved
into IRAM (on the iRiver). This was enough to make the decoder work
in real-time.
A point of interest - the -O3 gcc option (the setting used in the
original Makefile provided with the alac decoder) gives a significant
speedup compared to -O2. With -O2, the Coldfire runs at a constant
120MHz, but with -O3, it can power-down to 40MHz for a small amount of
time.
The file alac.c contained some hints from the original author for
places where major optimisations can be made - specifically the
unrolling and optimisation of certain cases of general loops.
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