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https://github.com/RangeNetworks/openbts.git
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c0a5c1509e
git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@2242 19bc5d8c-e614-43d4-8b26-e1612bc8e597
604 lines
12 KiB
C++
604 lines
12 KiB
C++
/*
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* Copyright 2008, 2009 Free Software Foundation, Inc.
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*
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*
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* This software is distributed under the terms of the GNU Affero Public License.
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* See the COPYING file in the main directory for details.
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*
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* This use of this software may be subject to additional restrictions.
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* See the LEGAL file in the main directory for details.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU Affero General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Affero General Public License for more details.
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You should have received a copy of the GNU Affero General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "BitVector.h"
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#include <iostream>
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#include <stdio.h>
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using namespace std;
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/**
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Apply a Galois polymonial to a binary seqeunce.
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@param val The input sequence.
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@param poly The polynomial.
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@param order The order of the polynomial.
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@return Single-bit result.
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*/
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unsigned applyPoly(uint64_t val, uint64_t poly, unsigned order)
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{
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uint64_t prod = val & poly;
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unsigned sum = prod;
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for (unsigned i=1; i<order; i++) sum ^= prod>>i;
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return sum & 0x01;
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}
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BitVector::BitVector(const char *valString)
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:Vector<char>(strlen(valString))
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{
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uint32_t accum = 0;
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for (size_t i=0; i<size(); i++) {
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accum <<= 1;
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if (valString[i]=='1') accum |= 0x01;
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mStart[i] = accum;
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}
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}
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uint64_t BitVector::peekField(size_t readIndex, unsigned length) const
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{
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uint64_t accum = 0;
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char *dp = mStart + readIndex;
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assert(dp+length <= mEnd);
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for (unsigned i=0; i<length; i++) {
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accum = (accum<<1) | ((*dp++) & 0x01);
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}
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return accum;
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}
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uint64_t BitVector::peekFieldReversed(size_t readIndex, unsigned length) const
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{
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uint64_t accum = 0;
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char *dp = mStart + readIndex + length - 1;
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assert(dp<mEnd);
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for (int i=(length-1); i>=0; i--) {
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accum = (accum<<1) | ((*dp--) & 0x01);
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}
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return accum;
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}
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uint64_t BitVector::readField(size_t& readIndex, unsigned length) const
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{
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const uint64_t retVal = peekField(readIndex,length);
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readIndex += length;
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return retVal;
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}
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uint64_t BitVector::readFieldReversed(size_t& readIndex, unsigned length) const
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{
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const uint64_t retVal = peekFieldReversed(readIndex,length);
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readIndex += length;
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return retVal;
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}
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void BitVector::fillField(size_t writeIndex, uint64_t value, unsigned length)
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{
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char *dpBase = mStart + writeIndex;
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char *dp = dpBase + length - 1;
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assert(dp < mEnd);
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while (dp>=dpBase) {
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*dp-- = value & 0x01;
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value >>= 1;
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}
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}
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void BitVector::fillFieldReversed(size_t writeIndex, uint64_t value, unsigned length)
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{
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char *dp = mStart + writeIndex;
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char *dpEnd = dp + length - 1;
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assert(dpEnd < mEnd);
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while (dp<=dpEnd) {
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*dp++ = value & 0x01;
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value >>= 1;
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}
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}
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void BitVector::writeField(size_t& writeIndex, uint64_t value, unsigned length)
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{
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fillField(writeIndex,value,length);
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writeIndex += length;
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}
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void BitVector::writeFieldReversed(size_t& writeIndex, uint64_t value, unsigned length)
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{
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fillFieldReversed(writeIndex,value,length);
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writeIndex += length;
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}
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void BitVector::invert()
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{
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for (size_t i=0; i<size(); i++) {
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mStart[i] = ~mStart[i];
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}
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}
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void BitVector::reverse8()
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{
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assert(size()>=8);
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char tmp0 = mStart[0];
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mStart[0] = mStart[7];
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mStart[7] = tmp0;
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char tmp1 = mStart[1];
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mStart[1] = mStart[6];
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mStart[6] = tmp1;
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char tmp2 = mStart[2];
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mStart[2] = mStart[5];
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mStart[5] = tmp2;
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char tmp3 = mStart[3];
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mStart[3] = mStart[4];
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mStart[4] = tmp3;
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}
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void BitVector::LSB8MSB()
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{
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if (size()<8) return;
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size_t size8 = 8*(size()/8);
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size_t iTop = size8 - 8;
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for (size_t i=0; i<=iTop; i+=8) segment(i,8).reverse8();
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}
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uint64_t BitVector::syndrome(Generator& gen) const
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{
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gen.clear();
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const char *dp = mStart;
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while (dp<mEnd) gen.syndromeShift(*dp++);
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return gen.state();
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}
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uint64_t BitVector::parity(Generator& gen) const
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{
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gen.clear();
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const char *dp = mStart;
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while (dp<mEnd) gen.encoderShift(*dp++);
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return gen.state();
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}
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void BitVector::encode(const ViterbiR2O4& coder, BitVector& target)
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{
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size_t sz = size();
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assert(sz*coder.iRate() == target.size());
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// Build a "history" array where each element contains the full history.
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uint32_t history[sz];
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uint32_t accum = 0;
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for (size_t i=0; i<sz; i++) {
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accum = (accum<<1) | bit(i);
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history[i] = accum;
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}
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// Look up histories in the pre-generated state table.
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char *op = target.begin();
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for (size_t i=0; i<sz; i++) {
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unsigned index = coder.cMask() & history[i];
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for (unsigned g=0; g<coder.iRate(); g++) {
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*op++ = coder.stateTable(g,index);
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}
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}
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}
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unsigned BitVector::sum() const
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{
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unsigned sum = 0;
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for (size_t i=0; i<size(); i++) sum += mStart[i] & 0x01;
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return sum;
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}
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void BitVector::map(const unsigned *map, size_t mapSize, BitVector& dest) const
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{
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for (unsigned i=0; i<mapSize; i++) {
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dest.mStart[i] = mStart[map[i]];
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}
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}
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void BitVector::unmap(const unsigned *map, size_t mapSize, BitVector& dest) const
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{
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for (unsigned i=0; i<mapSize; i++) {
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dest.mStart[map[i]] = mStart[i];
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}
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}
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ostream& operator<<(ostream& os, const BitVector& hv)
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{
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for (size_t i=0; i<hv.size(); i++) {
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if (hv.bit(i)) os << '1';
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else os << '0';
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}
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return os;
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}
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ViterbiR2O4::ViterbiR2O4()
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{
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assert(mDeferral < 32);
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mCoeffs[0] = 0x019;
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mCoeffs[1] = 0x01b;
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computeStateTables(0);
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computeStateTables(1);
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computeGeneratorTable();
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}
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void ViterbiR2O4::initializeStates()
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{
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for (unsigned i=0; i<mIStates; i++) clear(mSurvivors[i]);
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for (unsigned i=0; i<mNumCands; i++) clear(mCandidates[i]);
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}
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void ViterbiR2O4::computeStateTables(unsigned g)
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{
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assert(g<mIRate);
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for (unsigned state=0; state<mIStates; state++) {
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// 0 input
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uint32_t inputVal = state<<1;
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mStateTable[g][inputVal] = applyPoly(inputVal, mCoeffs[g], mOrder+1);
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// 1 input
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inputVal |= 1;
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mStateTable[g][inputVal] = applyPoly(inputVal, mCoeffs[g], mOrder+1);
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}
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}
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void ViterbiR2O4::computeGeneratorTable()
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{
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for (unsigned index=0; index<mIStates*2; index++) {
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mGeneratorTable[index] = (mStateTable[0][index]<<1) | mStateTable[1][index];
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}
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}
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void ViterbiR2O4::branchCandidates()
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{
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// Branch to generate new input states.
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const vCand *sp = mSurvivors;
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for (unsigned i=0; i<mNumCands; i+=2) {
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// extend and suffix
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const uint32_t iState0 = (sp->iState) << 1; // input state for 0
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const uint32_t iState1 = iState0 | 0x01; // input state for 1
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const uint32_t oStateShifted = (sp->oState) << mIRate; // shifted output
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const float cost = sp->cost;
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sp++;
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// 0 input extension
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mCandidates[i].cost = cost;
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mCandidates[i].oState = oStateShifted | mGeneratorTable[iState0 & mCMask];
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mCandidates[i].iState = iState0;
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// 1 input extension
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mCandidates[i+1].cost = cost;
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mCandidates[i+1].oState = oStateShifted | mGeneratorTable[iState1 & mCMask];
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mCandidates[i+1].iState = iState1;
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}
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}
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void ViterbiR2O4::getSoftCostMetrics(const uint32_t inSample, const float *matchCost, const float *mismatchCost)
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{
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const float *cTab[2] = {matchCost,mismatchCost};
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for (unsigned i=0; i<mNumCands; i++) {
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vCand& thisCand = mCandidates[i];
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// We examine input bits 2 at a time for a rate 1/2 coder.
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const unsigned mismatched = inSample ^ (thisCand.oState);
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thisCand.cost += cTab[mismatched&0x01][1] + cTab[(mismatched>>1)&0x01][0];
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}
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}
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void ViterbiR2O4::pruneCandidates()
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{
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const vCand* c1 = mCandidates; // 0-prefix
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const vCand* c2 = mCandidates + mIStates; // 1-prefix
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for (unsigned i=0; i<mIStates; i++) {
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if (c1[i].cost < c2[i].cost) mSurvivors[i] = c1[i];
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else mSurvivors[i] = c2[i];
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}
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}
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const ViterbiR2O4::vCand& ViterbiR2O4::minCost() const
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{
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int minIndex = 0;
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float minCost = mSurvivors[0].cost;
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for (unsigned i=1; i<mIStates; i++) {
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const float thisCost = mSurvivors[i].cost;
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if (thisCost>=minCost) continue;
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minCost = thisCost;
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minIndex=i;
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}
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return mSurvivors[minIndex];
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}
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const ViterbiR2O4::vCand& ViterbiR2O4::step(uint32_t inSample, const float *probs, const float *iprobs)
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{
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branchCandidates();
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getSoftCostMetrics(inSample,probs,iprobs);
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pruneCandidates();
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return minCost();
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}
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uint64_t Parity::syndrome(const BitVector& receivedCodeword)
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{
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return receivedCodeword.syndrome(*this);
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}
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void Parity::writeParityWord(const BitVector& data, BitVector& parityTarget, bool invert)
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{
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uint64_t pWord = data.parity(*this);
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if (invert) pWord = ~pWord;
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parityTarget.fillField(0,pWord,size());
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}
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SoftVector::SoftVector(const BitVector& source)
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{
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resize(source.size());
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for (size_t i=0; i<size(); i++) {
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if (source.bit(i)) mStart[i]=1.0F;
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else mStart[i]=0.0F;
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}
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}
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BitVector SoftVector::sliced() const
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{
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size_t sz = size();
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BitVector newSig(sz);
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for (size_t i=0; i<sz; i++) {
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if (mStart[i]>0.5F) newSig[i]=1;
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else newSig[i] = 0;
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}
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return newSig;
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}
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void SoftVector::decode(ViterbiR2O4 &decoder, BitVector& target) const
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{
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const size_t sz = size();
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const unsigned deferral = decoder.deferral();
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const size_t ctsz = sz + deferral*decoder.iRate();
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assert(sz <= decoder.iRate()*target.size());
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// Build a "history" array where each element contains the full history.
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uint32_t history[ctsz];
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{
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BitVector bits = sliced();
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uint32_t accum = 0;
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for (size_t i=0; i<sz; i++) {
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accum = (accum<<1) | bits.bit(i);
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history[i] = accum;
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}
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// Repeat last bit at the end.
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for (size_t i=sz; i<ctsz; i++) {
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accum = (accum<<1) | (accum & 0x01);
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history[i] = accum;
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}
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}
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// Precompute metric tables.
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float matchCostTable[ctsz];
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float mismatchCostTable[ctsz];
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{
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const float *dp = mStart;
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for (size_t i=0; i<sz; i++) {
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// pVal is the probability that a bit is correct.
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// ipVal is the probability that a bit is incorrect.
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float pVal = dp[i];
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if (pVal>0.5F) pVal = 1.0F-pVal;
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float ipVal = 1.0F-pVal;
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// This is a cheap approximation to an ideal cost function.
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if (pVal<0.01F) pVal = 0.01;
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if (ipVal<0.01F) ipVal = 0.01;
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matchCostTable[i] = 0.25F/ipVal;
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mismatchCostTable[i] = 0.25F/pVal;
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}
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// pad end of table with unknowns
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for (size_t i=sz; i<ctsz; i++) {
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matchCostTable[i] = 0.5F;
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mismatchCostTable[i] = 0.5F;
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}
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}
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{
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decoder.initializeStates();
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// Each sample of history[] carries its history.
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// So we only have to process every iRate-th sample.
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const unsigned step = decoder.iRate();
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// input pointer
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const uint32_t *ip = history + step - 1;
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// output pointers
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char *op = target.begin();
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const char *const opt = target.end();
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// table pointers
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const float* match = matchCostTable;
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const float* mismatch = mismatchCostTable;
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size_t oCount = 0;
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while (op<opt) {
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// Viterbi algorithm
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assert(match-matchCostTable<sizeof(matchCostTable)/sizeof(matchCostTable[0])-1);
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assert(mismatch-mismatchCostTable<sizeof(mismatchCostTable)/sizeof(mismatchCostTable[0])-1);
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const ViterbiR2O4::vCand &minCost = decoder.step(*ip, match, mismatch);
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ip += step;
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match += step;
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mismatch += step;
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// output
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if (oCount>=deferral) *op++ = (minCost.iState >> deferral)&0x01;
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oCount++;
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}
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}
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}
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ostream& operator<<(ostream& os, const SoftVector& sv)
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{
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for (size_t i=0; i<sv.size(); i++) {
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if (sv[i]<0.25) os << "0";
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else if (sv[i]>0.75) os << "1";
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else os << "-";
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}
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return os;
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}
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void BitVector::pack(unsigned char* targ) const
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{
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// Assumes MSB-first packing.
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unsigned bytes = size()/8;
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for (unsigned i=0; i<bytes; i++) {
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targ[i] = peekField(i*8,8);
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}
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unsigned whole = bytes*8;
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unsigned rem = size() - whole;
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if (rem==0) return;
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targ[bytes] = peekField(whole,rem) << (8-rem);
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}
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void BitVector::unpack(const unsigned char* src)
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{
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// Assumes MSB-first packing.
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unsigned bytes = size()/8;
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for (unsigned i=0; i<bytes; i++) {
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fillField(i*8,src[i],8);
|
|
}
|
|
unsigned whole = bytes*8;
|
|
unsigned rem = size() - whole;
|
|
if (rem==0) return;
|
|
fillField(whole,src[bytes],rem);
|
|
}
|
|
|
|
void BitVector::hex(ostream& os) const
|
|
{
|
|
os << std::hex;
|
|
unsigned digits = size()/4;
|
|
size_t wp=0;
|
|
for (unsigned i=0; i<digits; i++) {
|
|
os << readField(wp,4);
|
|
}
|
|
os << std::dec;
|
|
}
|
|
|
|
bool BitVector::unhex(const char* src)
|
|
{
|
|
// Assumes MSB-first packing.
|
|
unsigned int val;
|
|
unsigned digits = size()/4;
|
|
for (unsigned i=0; i<digits; i++) {
|
|
if (sscanf(src+i, "%1x", &val) < 1) {
|
|
return false;
|
|
}
|
|
fillField(i*4,val,4);
|
|
}
|
|
unsigned whole = digits*4;
|
|
unsigned rem = size() - whole;
|
|
if (rem>0) {
|
|
if (sscanf(src+digits, "%1x", &val) < 1) {
|
|
return false;
|
|
}
|
|
fillField(whole,val,rem);
|
|
}
|
|
return true;
|
|
}
|
|
|
|
// vim: ts=4 sw=4
|