1COPYRIGHT 2 3This package is copyright 2006 by Phil Karn, KA9Q. It may be used 4under the terms of the GNU Lesser General Public License (LGPL). See 5the file "lesser.txt" in this package for license details. 6 7INTRODUCTION 8 9This package provides a set of functions that implement several 10popular forward error correction (FEC) algorithms and several low-level routines 11useful in modems implemented with digital signal processing (DSP). 12 13The following routines are provided: 14 151. Viterbi decoders for the following convolutional codes: 16 17r=1/2 k=7 ("Voyager" code, now a widely used industry standard) 18r=1/2 k=9 (Used on the IS-95 CDMA forward link) 19r=1/6 k=15 ("Cassini" code, used by several NASA/JPL deep space missions) 20 212. Reed-Solomon encoders and decoders for any user-specified code. 22 233. Optimized encoder and decoder for the CCSDS-standard (255,223) 24Reed-Solomon code, with and without the CCSDS-standard "dual basis" 25symbol representation. 26 274. Compute dot product between a 16-bit buffer and a set of 16-bit 28coefficients. This is the basic DSP primitive for digital filtering 29and correlation. 30 314. Compute sum of squares of a buffer of 16-bit signed integers. This is 32useful in DSP for finding the total energy in a signal. 33 345. Find peak value in a buffer of 16-bit signed integers, useful for 35scaling a signal to prevent overflow. 36 37SIMD SUPPORT 38 39This package automatically makes use of various SIMD (Single 40Instruction stream, Multiple Data stream) instruction sets, when 41available: MMX, SSE and SSE2 on the IA-32 (Intel) architecture, and 42Altivec on the PowerPC G4 and G5 used by Power Macintoshes. 43 44"Altivec" is a Motorola trademark; Apple calls it "Velocity Engine", 45and IBM calls it "VMX". Altivec is roughly comparable to SSE2 on the 46IA-32. 47 48Many of the SIMD versions run more than an order of 49magnitude faster than their portable C versions. The available SIMD 50instruction sets, if any, are determined at run time and the proper 51version of each routine is automatically selected. If no SIMD 52instructions are available, the portable C version is invoked by 53default. On targets other than IA-32 and PPC, only the portable C 54version is built. 55 56The SIMD-assisted versions generally produce the same results as the C 57versions, with a few minor exceptions. The Viterbi decoders in C have 58a very slightly greater Eb/No performance due to their use of 32-bit 59path metrics. On the other hand, the SIMD versions use the 60"saturating" arithmetic available in these instructions to avoid the 61integer wraparounds that can occur in C when argument ranges are not 62properly constrained. This applies primarily to the "dotprod" (dot 63product) function. 64 65The MMX (MultiMedia eXtensions) instruction set was introduced on 66later Pentium CPUs; it is also implemented on the Pentium II and most 67AMD CPUs starting with the K6. SSE (SIMD Streaming Extensions) was 68introduced in the Pentium III; AMD calls it "3D Now! Professional". 69Intel introduced SSE2 on the Pentium 4, and it has been picked up by 70later AMD CPUs. SSE support implies MMX support, while SSE2 support 71implies both SSE and MMX support. 72 73The latest IA-32 SIMD instruction set, SSE3 (also known as "Prescott 74New Instructions") was introduced in early 2004 with the latest 75("Prescott") revision of the Pentium 4. Relatively little was 76introduced with SSE3, and this library currently makes no use of it. 77 78See the various manual pages for details on how to use the library 79routines. 80 81Copyright 2006, Phil Karn, KA9Q 82karn@ka9q.net 83http://www.ka9q.net/ 84 85This software may be used under the terms of the GNU Lesser General 86Public License (LGPL); see the file lesser.txt for details. 87 88Revision history: 89Version 1.0 released 29 May 2001 90 91Version 2.0 released 3 Dec 2001: 92Restructured to add support for shared libraries. 93 94Version 2.0.1 released 8 Dec 2001: 95Includes autoconf/configure script 96 97Version 2.0.2 released 4 Feb 2002: 98Add SIMD version override options 99Test for lack of SSE2 mnemonic support in 'as' 100Build only selected version 101 102Version 2.0.3 released 6 Feb 2002: 103Fix to parityb function in parity.h 104 105feclib version 1.0 released November 2003 106Merged SIMD-Viterbi, RS and DSP libraries 107Changed SIMD Viterbi decoder to detect SSE2/SSE/MMX at runtime rather than build time 108 109feclib version 2.0 (unreleased) Mar 2004 110General speedups and cleanups 111Switch from 4 to 8-bit input symbols on all Viterbi decoders 112Support for Altivec on PowerPC 113Support for k=15 r=1/6 Cassini/Mars Pathfinder/Mars Exploration Rover/STEREO code 114Changed license to GNU Lesser General Public License (LGPL) 115 116feclib version 2.1 June 5 2006 117Added error checking, fixed alignment bug in SSE2 versions of Viterbi decoders causing segfaults 118 119feclib version 2.1.1 June 6 2006 120Fix test/benchmark time measurement on Linux 121