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58 lines
1.3 KiB
Python
58 lines
1.3 KiB
Python
# brute-force search for access descriptor hash table
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modes = [
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"1",
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"L", "LA",
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"I", "I;16", "I;16L", "I;16B", "I;32L", "I;32B",
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"F",
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"P", "PA",
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"RGB", "RGBA", "RGBa", "RGBX",
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"CMYK",
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"YCbCr",
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]
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def hash(s, i):
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# djb2 hash: multiply by 33 and xor character
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for c in s:
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i = (((i << 5) + i) ^ ord(c)) & 0xffffffff
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return i
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def check(size, i0):
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h = [None] * size
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for m in modes:
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i = hash(m, i0)
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i = i % size
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if h[i]:
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return 0
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h[i] = m
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return h
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min_start = 0
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# 1) find the smallest table size with no collisions
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for min_size in range(len(modes), 16384):
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if check(min_size, 0):
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print(len(modes), "modes fit in", min_size, "slots")
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break
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# 2) see if we can do better with a different initial value
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for i0 in range(65556):
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for size in range(1, min_size):
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if check(size, i0):
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if size < min_size:
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print(len(modes), "modes fit in", size, "slots with start", i0)
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min_size = size
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min_start = i0
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print()
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# print check(min_size, min_start)
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print("#define ACCESS_TABLE_SIZE", min_size)
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print("#define ACCESS_TABLE_HASH", min_start)
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# for m in modes:
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# print m, "=>", hash(m, min_start) % min_size
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