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Code Issues 295 Packages Projects Releases 20 Wiki Activity

Take sligthly more academic approach

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This commit is contained in:
Matt Nadareski
2023-01-03 00:12:31 -08:00
parent 5e2d7505da
commit c28de855e2
1 changed files with 53 additions and 30 deletions
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83
BurnOutSharp.Compression/Quantum/Decompressor.cs
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@@ -402,8 +402,7 @@ namespace BurnOutSharp.Compression.Quantum
/// </summary>
private static ushort GET_SYMBOL(Model model, ref ushort H, ref ushort L, ref ushort C, byte[] inbuf, ref int inpos, ref int bitsleft, ref uint bitbuf)
{
uint range = (uint)(((H - L) & 0xFFFF) + 1);
ushort symf = (ushort)(((((C - L + 1) * model.Symbols[0].CumulativeFrequency) - 1) / range) & 0xFFFF);
ushort symf = GetFrequency(model.Symbols[0].CumulativeFrequency, H, L, C);
int i;
for (i = 1; i < model.Entries; i++)
@@ -413,39 +412,63 @@ namespace BurnOutSharp.Compression.Quantum
}
ushort symbol = model.Symbols[i - 1].Symbol;
range = (uint)(H - L + 1);
H = (ushort)(L + ((model.Symbols[i - 1].CumulativeFrequency * range) / model.Symbols[0].CumulativeFrequency) - 1);
L = (ushort)(L + ((model.Symbols[i].CumulativeFrequency * range) / model.Symbols[0].CumulativeFrequency));
while (true)
{
if ((L & 0x8000) != (H & 0x8000))
{
// Underflow case
if ((L & 0x4000) != 0 && (H & 0x4000) == 0)
{
C ^= 0x4000;
L &= 0x3FFF;
H |= 0x4000;
}
else
{
break;
}
}
L <<= 1;
H = (ushort)((H << 1) | 1);
Q_FILL_BUFFER(inbuf, ref inpos, ref bitsleft, ref bitbuf);
C = (ushort)((C << 1) | Q_PEEK_BITS(1, bitbuf));
Q_REMOVE_BITS(1, ref bitsleft, ref bitbuf);
}
GetCode(model.Symbols[i - 1].CumulativeFrequency,
model.Symbols[i].CumulativeFrequency,
model.Symbols[0].CumulativeFrequency,
ref H, ref L, ref C,
inbuf, ref inpos, ref bitsleft, ref bitbuf);
UpdateModel(model, i);
return symbol;
}
/// <summary>
/// Get the frequency for a given range and total frequency
/// </summary>
private static ushort GetFrequency(ushort totalFrequency, ushort H, ushort L, ushort C)
{
uint range = (uint)(((H - L) & 0xFFFF) + 1);
uint freq = (uint)(((C - L + 1) * totalFrequency - 1) / range);
return (ushort)(freq & 0xFFFF);
}
/// <summary>
/// The decoder renormalization loop
/// </summary>
private static void GetCode(int previousFrequency,
int cumulativeFrequency,
int totalFrequency,
ref ushort H,
ref ushort L,
ref ushort C,
byte[] inbuf,
ref int inpos,
ref int bitsleft,
ref uint bitbuf)
{
uint range = (uint)((H - L) + 1);
H = (ushort)(L + ((previousFrequency * range) / totalFrequency) - 1);
L = (ushort)(L + (cumulativeFrequency * range) / totalFrequency);
while (true)
{
if ((L & 0x8000) != (H & 0x8000))
{
if ((L & 0x4000) == 0 || (H & 0x4000) != 0)
break;
// Underflow case
C ^= 0x4000;
L &= 0x3FFF;
H |= 0x4000;
}
L <<= 1;
H = (ushort)((H << 1) | 1);
C = (ushort)((C << 1) | Q_READ_BITS(1, inbuf, ref inpos, ref bitsleft, ref bitbuf));
}
}
#endregion
}
}