chris/js8call
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Added varicode encoding of messages

Browse Source 
What this does is allow us to pack more than 13 characters in a single
transmission frame. Optimized using a Huffman encoding using weights of
alphabetical frequency, this will often allow us to send less than 5 bits
per character.
This commit is contained in:
Jordan Sherer
2018-07-19 03:44:02 -04:00
parent 512dffabf4
commit b8267372e4
5 changed files with 146 additions and 39 deletions
Download Patch File Download Diff File Expand all files Collapse all files
varicode.cpp
+66 -8
View File
@@ -175,10 +175,10 @@ QVector<bool> Varicode::huffFlatten(QList<QVector<bool>> &list){
return out;
}
QString Varicode::huffDecode(QVector<bool> const& bitvec){
QString Varicode::huffDecode(QVector<bool> const& bitvec, int pad){
QString out;
QString bits = bitsToStr(bitvec);
QString bits = bitsToStr(bitvec).mid(0, bitvec.length()-pad);
// TODO: jsherer - this is naive...
while(bits.length() > 0){
@@ -538,6 +538,7 @@ QString Varicode::packDirectedMessage(const QString &text, const QString &callsi
auto fromBytes = from.toLocal8Bit();
auto fromCRC = CRC::Calculate(fromBytes.data(), fromBytes.length(), CRC::CRC_5_ITU());
quint8 packed_is_data = 0;
quint8 packed_flag = 0;
quint32 packed_from = Varicode::packCallsign(from);
quint32 packed_to = Varicode::packCallsign(to);
@@ -550,18 +551,18 @@ QString Varicode::packDirectedMessage(const QString &text, const QString &callsi
quint8 packed_cmd = directed_cmds[cmd];
quint8 packed_extra = fromCRC;
// [3][28][28][5],[5] = 69
// [1][2][28][28][5],[5] = 69
auto bits = (
Varicode::intToBits(packed_flag, 3) +
Varicode::intToBits(packed_is_data, 1) +
Varicode::intToBits(packed_flag, 2) +
Varicode::intToBits(packed_from, 28) +
Varicode::intToBits(packed_to, 28) +
Varicode::intToBits(packed_cmd & 31, 5)
);
frame = Varicode::pack64bits(Varicode::bitsToInt(bits)) + Varicode::pack5bits(packed_extra & 31);
*n = match.captured(0).length();
return frame;
}
return frame;
}
QStringList Varicode::unpackDirectedMessage(const QString &text){
@@ -571,11 +572,15 @@ QStringList Varicode::unpackDirectedMessage(const QString &text){
return unpacked;
}
// [3][28][28][5],[5] = 69
// [1][2][28][28][5],[5] = 69
auto bits = Varicode::bitsToStr(Varicode::intToBits(Varicode::unpack64bits(text.left(12)), 64));
quint8 extra = Varicode::unpack5bits(text.right(1));
quint8 flag = Varicode::bitsToInt(Varicode::strToBits(bits.left(3)));
quint8 is_data = Varicode::bitsToInt(Varicode::strToBits(bits.left(1)));
if(is_data != 0){
return unpacked;
}
quint8 flag = Varicode::bitsToInt(Varicode::strToBits(bits.mid(1,2)));
quint32 packed_from = Varicode::bitsToInt(Varicode::strToBits(bits.mid(3, 28)));
quint32 packed_to = Varicode::bitsToInt(Varicode::strToBits(bits.mid(31, 28)));
quint8 packed_cmd = Varicode::bitsToInt(Varicode::strToBits(bits.mid(59, 5)));
@@ -594,3 +599,56 @@ QStringList Varicode::unpackDirectedMessage(const QString &text){
return unpacked;
}
QString Varicode::packDataMessage(const QString &text, int *n){
QString frame;
// [1][63],[5]
quint8 is_data = 1;
auto frameBits = (
Varicode::intToBits(is_data, 1)
);
int i = 0;
foreach(auto charBits, Varicode::huffEncode(text)){
if(frameBits.length() + charBits.length() < 63){
frameBits += charBits;
i++;
continue;
}
break;
}
int pad = 64 - frameBits.length();
if(pad){
frameBits += Varicode::intToBits(1, pad);
}
frame = Varicode::pack64bits(Varicode::bitsToInt(frameBits)) + Varicode::pack5bits(pad & 31);
*n = i;
return frame;
}
QString Varicode::unpackDataMessage(const QString &text){
QString unpacked;
if(text.length() < 13){
return unpacked;
}
auto bits = Varicode::intToBits(Varicode::unpack64bits(text.left(12)), 64);
quint8 pad = Varicode::unpack5bits(text.right(1));
quint8 is_data = (int)bits.at(0);
if(is_data != 1){
return unpacked;
}
// pop off the is_data bit
bits.removeAt(0);
unpacked = Varicode::huffDecode(bits, pad);
return unpacked;
}