35 lines
748 B
Nim
35 lines
748 B
Nim
type
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Bools[N: static int] = array[N, bool]
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SumCarry = tuple[sum, carry: bool]
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proc ha(a, b: bool): SumCarry = (a xor b, a and b)
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proc fa(a, b, ci: bool): SumCarry =
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let a = ha(ci, a)
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let b = ha(a[0], b)
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result = (b[0], a[1] or b[1])
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proc fa4(a, b: Bools[4]): Bools[5] =
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var co, s: Bools[4]
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for i in 0..3:
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let r = fa(a[i], b[i], if i > 0: co[i-1] else: false)
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s[i] = r[0]
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co[i] = r[1]
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result[0..3] = s
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result[4] = co[3]
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proc int2bus(n: int): Bools[4] =
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var n = n
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for i in 0..result.high:
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result[i] = (n and 1) == 1
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n = n shr 1
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proc bus2int(b: Bools): int =
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for i, x in b:
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result += (if x: 1 else: 0) shl i
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for a in 0..7:
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for b in 0..7:
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assert a + b == bus2int fa4(int2bus(a), int2bus(b))
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