Data commit

Task/Four-bit-adder/Nim/four-bit-adder.nim

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