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https://github.com/cuberite/libdeflate.git
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88d45c7e1c
Reduce the memory usage of compression levels 1-9 by using the condensed offset slot map instead of the full one.
42 lines
1.4 KiB
Python
Executable File
42 lines
1.4 KiB
Python
Executable File
#!/usr/bin/env python3
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#
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# This script generates the deflate_offset_slot[] array, which is a condensed
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# map from offsets to offset slots.
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DEFLATE_OFFSET_SLOT_BASE = [
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1 , 2 , 3 , 4 , 5 , 7 , 9 , 13 ,
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17 , 25 , 33 , 49 , 65 , 97 , 129 , 193 ,
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257 , 385 , 513 , 769 , 1025 , 1537 , 2049 , 3073 ,
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4097 , 6145 , 8193 , 12289 , 16385 , 24577 ,
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]
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DEFLATE_EXTRA_OFFSET_BITS = [
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0 , 0 , 0 , 0 , 1 , 1 , 2 , 2 ,
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3 , 3 , 4 , 4 , 5 , 5 , 6 , 6 ,
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7 , 7 , 8 , 8 , 9 , 9 , 10 , 10 ,
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11 , 11 , 12 , 12 , 13 , 13 ,
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]
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offset_slot_map = [0] * 512
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for offset_slot, offset_base in enumerate(DEFLATE_OFFSET_SLOT_BASE):
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num_extra_bits = DEFLATE_EXTRA_OFFSET_BITS[offset_slot]
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offset_end = offset_base + (1 << num_extra_bits)
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if offset_base <= 256:
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for offset in range(offset_base, offset_end):
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offset_slot_map[offset] = offset_slot
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else:
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for offset in range(offset_base, offset_end, 128):
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offset_slot_map[256 + ((offset - 1) >> 7)] = offset_slot
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print('static const u8 deflate_offset_slot_map[512] = {')
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for i in range(0, len(offset_slot_map), 16):
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print('\t', end='')
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for j, v in enumerate(offset_slot_map[i:i+16]):
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print(f'{v},', end='')
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if j == 15:
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print('')
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else:
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print(' ', end='')
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print('};')
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