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Symbols for codes shorter than the prefix table index width are stored in the table. All the entries in the table with an index starting with the code are set to the symbol value. That way, when decoding it is possible to get the number of bits corresponding to the table width from the bitstream and directly find the symbol value. Longer code still need to be searched for in the codes list.
98 lines
2.7 KiB
C++
98 lines
2.7 KiB
C++
#include <cxxtest/TestSuite.h>
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#include "common/huffman.h"
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#include "common/bitstream.h"
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#include "common/memstream.h"
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/**
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* A test suite for the Huffman decoder in common/huffman.h
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* The encoding used comes from the example on the Wikipedia page
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* for Huffman.
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* TODO: It could be improved by generating one at runtime.
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*/
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class HuffmanTestSuite : public CxxTest::TestSuite {
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public:
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void test_get_with_full_symbols() {
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/*
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* The class can be initialized with or without providing
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* a max_length and a symbol table.
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* We test with a table.
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*
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* Encoding (arbitrary, for testing purpouses):
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* 0xA=010
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* 0xB=011
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* 0xC=11
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* 0xD=00
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* 0xE=10
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*/
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uint32 codeCount = 5;
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uint8 maxLength = 3;
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const uint8 lengths[] = {3,3,2,2,2};
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const uint32 codes[] = {0x2, 0x3, 0x3, 0x0, 0x2};
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const uint32 symbols[] = {0xA, 0xB, 0xC, 0xD, 0xE};
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Common::Huffman<Common::BitStream8MSB> h(maxLength, codeCount, codes, lengths, symbols);
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byte input[] = {0x4F, 0x20};
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// Provided input...
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uint32 expected[] = {0xA, 0xB, 0xC, 0xD, 0xE, 0xD, 0xD};
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// ..and expected output.
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/*
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* What should be going on:
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* 010 011 11 00 10 00 00 = A B C D E D D
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* = 0100 1111 0010 0000 = 0x4F20
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*/
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Common::MemoryReadStream ms(input, sizeof(input));
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Common::BitStream8MSB bs(ms);
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TS_ASSERT_EQUALS(h.getSymbol(bs), expected[0]);
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TS_ASSERT_EQUALS(h.getSymbol(bs), expected[1]);
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TS_ASSERT_EQUALS(h.getSymbol(bs), expected[2]);
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TS_ASSERT_EQUALS(h.getSymbol(bs), expected[3]);
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TS_ASSERT_EQUALS(h.getSymbol(bs), expected[4]);
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TS_ASSERT_EQUALS(h.getSymbol(bs), expected[5]);
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TS_ASSERT_EQUALS(h.getSymbol(bs), expected[6]);
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}
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void test_get_without_symbols() {
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/*
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* This is basically the same as test_get_with_full_symbols, but
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* I only pass the minimal required arguments.
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* Specifically, I avoid passing the symbols table, so that
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* array indices are used instead.
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*
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* Encoding becomes:
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*
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* 0=010
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* 1=011
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* 2=11
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* 3=00
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* 4=10
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*/
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uint32 codeCount = 5;
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const uint8 lengths[] = {3,3,2,2,2};
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const uint32 codes[] = {0x2, 0x3, 0x3, 0x0, 0x2};
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Common::Huffman<Common::BitStream8MSB> h(0, codeCount, codes, lengths, 0);
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byte input[] = {0x4F, 0x20};
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uint32 expected[] = {0, 1, 2, 3, 4, 3 ,3};
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Common::MemoryReadStream ms(input, sizeof(input));
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Common::BitStream8MSB bs(ms);
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TS_ASSERT_EQUALS(h.getSymbol(bs), expected[0]);
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TS_ASSERT_EQUALS(h.getSymbol(bs), expected[1]);
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TS_ASSERT_EQUALS(h.getSymbol(bs), expected[2]);
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TS_ASSERT_EQUALS(h.getSymbol(bs), expected[3]);
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TS_ASSERT_EQUALS(h.getSymbol(bs), expected[4]);
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TS_ASSERT_EQUALS(h.getSymbol(bs), expected[5]);
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TS_ASSERT_EQUALS(h.getSymbol(bs), expected[6]);
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}
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};
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