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.