Use a lookup table for decoding #43
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According to "measure_time.cpp" benchmark, decoding is 2.55 (g++ -O3) / 2.65 (g++ -O0) times slower than encoding. One of the bottleneck comes from doing several comparisons and calculating the value for each decoded character. Replacing the comparison + calculation by a lookup table (like in the encoding) improves the decoding speed, making it only 2.22 (g++ -O0) / 1.36 (g++ -O2) times slower than encoding.
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According to "measure_time.cpp" benchmark, decoding is 2.55 (g++ -O3) / 2.65 (g++ -O0) times slower than encoding. One of the bottleneck comes from doing several comparisons and calculating the value for each decoded character. Replacing the comparison + calculation by a lookup table (like in the encoding) improves the decoding speed, making it only 2.22 (g++ -O0) / 1.36 (g++ -O2) times slower than encoding.
Cherry-picked from: #27