kopia lustrzana https://github.com/cyoung/stratux
121 wiersze
4.6 KiB
Plaintext
121 wiersze
4.6 KiB
Plaintext
COPYRIGHT
|
|
|
|
This package is copyright 2006 by Phil Karn, KA9Q. It may be used
|
|
under the terms of the GNU Lesser General Public License (LGPL). See
|
|
the file "lesser.txt" in this package for license details.
|
|
|
|
INTRODUCTION
|
|
|
|
This package provides a set of functions that implement several
|
|
popular forward error correction (FEC) algorithms and several low-level routines
|
|
useful in modems implemented with digital signal processing (DSP).
|
|
|
|
The following routines are provided:
|
|
|
|
1. Viterbi decoders for the following convolutional codes:
|
|
|
|
r=1/2 k=7 ("Voyager" code, now a widely used industry standard)
|
|
r=1/2 k=9 (Used on the IS-95 CDMA forward link)
|
|
r=1/6 k=15 ("Cassini" code, used by several NASA/JPL deep space missions)
|
|
|
|
2. Reed-Solomon encoders and decoders for any user-specified code.
|
|
|
|
3. Optimized encoder and decoder for the CCSDS-standard (255,223)
|
|
Reed-Solomon code, with and without the CCSDS-standard "dual basis"
|
|
symbol representation.
|
|
|
|
4. Compute dot product between a 16-bit buffer and a set of 16-bit
|
|
coefficients. This is the basic DSP primitive for digital filtering
|
|
and correlation.
|
|
|
|
4. Compute sum of squares of a buffer of 16-bit signed integers. This is
|
|
useful in DSP for finding the total energy in a signal.
|
|
|
|
5. Find peak value in a buffer of 16-bit signed integers, useful for
|
|
scaling a signal to prevent overflow.
|
|
|
|
SIMD SUPPORT
|
|
|
|
This package automatically makes use of various SIMD (Single
|
|
Instruction stream, Multiple Data stream) instruction sets, when
|
|
available: MMX, SSE and SSE2 on the IA-32 (Intel) architecture, and
|
|
Altivec on the PowerPC G4 and G5 used by Power Macintoshes.
|
|
|
|
"Altivec" is a Motorola trademark; Apple calls it "Velocity Engine",
|
|
and IBM calls it "VMX". Altivec is roughly comparable to SSE2 on the
|
|
IA-32.
|
|
|
|
Many of the SIMD versions run more than an order of
|
|
magnitude faster than their portable C versions. The available SIMD
|
|
instruction sets, if any, are determined at run time and the proper
|
|
version of each routine is automatically selected. If no SIMD
|
|
instructions are available, the portable C version is invoked by
|
|
default. On targets other than IA-32 and PPC, only the portable C
|
|
version is built.
|
|
|
|
The SIMD-assisted versions generally produce the same results as the C
|
|
versions, with a few minor exceptions. The Viterbi decoders in C have
|
|
a very slightly greater Eb/No performance due to their use of 32-bit
|
|
path metrics. On the other hand, the SIMD versions use the
|
|
"saturating" arithmetic available in these instructions to avoid the
|
|
integer wraparounds that can occur in C when argument ranges are not
|
|
properly constrained. This applies primarily to the "dotprod" (dot
|
|
product) function.
|
|
|
|
The MMX (MultiMedia eXtensions) instruction set was introduced on
|
|
later Pentium CPUs; it is also implemented on the Pentium II and most
|
|
AMD CPUs starting with the K6. SSE (SIMD Streaming Extensions) was
|
|
introduced in the Pentium III; AMD calls it "3D Now! Professional".
|
|
Intel introduced SSE2 on the Pentium 4, and it has been picked up by
|
|
later AMD CPUs. SSE support implies MMX support, while SSE2 support
|
|
implies both SSE and MMX support.
|
|
|
|
The latest IA-32 SIMD instruction set, SSE3 (also known as "Prescott
|
|
New Instructions") was introduced in early 2004 with the latest
|
|
("Prescott") revision of the Pentium 4. Relatively little was
|
|
introduced with SSE3, and this library currently makes no use of it.
|
|
|
|
See the various manual pages for details on how to use the library
|
|
routines.
|
|
|
|
Copyright 2006, Phil Karn, KA9Q
|
|
karn@ka9q.net
|
|
http://www.ka9q.net/
|
|
|
|
This software may be used under the terms of the GNU Lesser General
|
|
Public License (LGPL); see the file lesser.txt for details.
|
|
|
|
Revision history:
|
|
Version 1.0 released 29 May 2001
|
|
|
|
Version 2.0 released 3 Dec 2001:
|
|
Restructured to add support for shared libraries.
|
|
|
|
Version 2.0.1 released 8 Dec 2001:
|
|
Includes autoconf/configure script
|
|
|
|
Version 2.0.2 released 4 Feb 2002:
|
|
Add SIMD version override options
|
|
Test for lack of SSE2 mnemonic support in 'as'
|
|
Build only selected version
|
|
|
|
Version 2.0.3 released 6 Feb 2002:
|
|
Fix to parityb function in parity.h
|
|
|
|
feclib version 1.0 released November 2003
|
|
Merged SIMD-Viterbi, RS and DSP libraries
|
|
Changed SIMD Viterbi decoder to detect SSE2/SSE/MMX at runtime rather than build time
|
|
|
|
feclib version 2.0 (unreleased) Mar 2004
|
|
General speedups and cleanups
|
|
Switch from 4 to 8-bit input symbols on all Viterbi decoders
|
|
Support for Altivec on PowerPC
|
|
Support for k=15 r=1/6 Cassini/Mars Pathfinder/Mars Exploration Rover/STEREO code
|
|
Changed license to GNU Lesser General Public License (LGPL)
|
|
|
|
feclib version 2.1 June 5 2006
|
|
Added error checking, fixed alignment bug in SSE2 versions of Viterbi decoders causing segfaults
|
|
|
|
feclib version 2.1.1 June 6 2006
|
|
Fix test/benchmark time measurement on Linux
|