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87 lines
1.5 KiB
C++
87 lines
1.5 KiB
C++
#include "deltastream.h"
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static int bitSize(quint8 baseSize, bool variableSign, bool extraBit)
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{
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int bits = 2;
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if (baseSize <= 9)
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bits += baseSize;
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else
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bits += 2 * baseSize - 9;
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if (variableSign)
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bits++;
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if (extraBit)
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bits++;
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return bits;
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}
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DeltaStream::DeltaStream(const SubFile &file, SubFile::Handle &hdl,
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quint32 length, quint8 info, bool extraBit, bool extended)
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: BitStream1(file, hdl, length), _readBits(0xFFFFFFFF)
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{
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_extraBit = extraBit ? 1 : 0;
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if (!(sign(_lonSign) && sign(_latSign)))
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return;
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if (extended) {
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quint32 b;
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if (!read(1, b))
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return;
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}
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_lonBits = bitSize(info & 0x0F, !_lonSign, extraBit);
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_latBits = bitSize(info >> 4, !_latSign, false);
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_readBits = _lonBits + _latBits;
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}
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bool DeltaStream::readDelta(int bits, int sign, int extraBit,
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qint32 &delta)
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{
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quint32 value;
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if (!read(bits, value))
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return false;
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value >>= extraBit;
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if (!sign) {
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qint32 signMask = 1 << (bits - extraBit - 1);
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if (value & signMask) {
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qint32 comp = value ^ signMask;
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if (comp)
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delta = comp - signMask;
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else {
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qint32 other;
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if (!readDelta(bits - extraBit, sign, false, other))
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return false;
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if (other < 0)
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delta = 1 - signMask + other;
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else
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delta = signMask - 1 + other;
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}
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} else {
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delta = value;
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}
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} else {
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delta = value * sign;
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}
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return true;
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}
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bool DeltaStream::sign(int &val)
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{
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quint32 bit;
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val = 0;
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if (!read(1, bit))
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return false;
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if (bit) {
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if (!read(1, bit))
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return false;
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val = bit ? -1 : 1;
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}
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return true;
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}
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