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34 lines
1.1 KiB
34 lines
1.1 KiB
8 years ago
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from utime import ticks_diff, ticks_add
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MAX = ticks_add(0, -1)
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# Should be done like this to avoid small int overflow
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MODULO_HALF = MAX // 2 + 1
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# Invariants:
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# if ticks_diff(a, b) = c,
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# then ticks_diff(b, a) = -c
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assert ticks_diff(1, 0) == 1, ticks_diff(1, 0)
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assert ticks_diff(0, 1) == -1
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assert ticks_diff(0, MAX) == 1
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assert ticks_diff(MAX, 0) == -1
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assert ticks_diff(0, MAX - 1) == 2
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# Maximum "positive" distance
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assert ticks_diff(MODULO_HALF, 1) == MODULO_HALF - 1, ticks_diff(MODULO_HALF, 1)
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# Step further, and it becomes a negative distance
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assert ticks_diff(MODULO_HALF, 0) == -MODULO_HALF
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# Offsetting that in either direction doesn't affect the result
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off = 100
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# Cheating and skipping to use ticks_add() when we know there's no wraparound
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# Real apps should use always it.
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assert ticks_diff(MODULO_HALF + off, 1 + off) == MODULO_HALF - 1
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assert ticks_diff(MODULO_HALF + off, 0 + off) == -MODULO_HALF
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assert ticks_diff(MODULO_HALF - off, ticks_add(1, -off)) == MODULO_HALF - 1
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assert ticks_diff(MODULO_HALF - off, ticks_add(0, -off)) == -MODULO_HALF
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print("OK")
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