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

@@ -0,0 +1,29 @@
+proc ha(a, b): auto = [a xor b, a and b] # sum, carry
+
+proc fa(a, b, ci): auto =
+  let a = ha(ci, a)
+  let b = ha(a[0], b)
+  [b[0], a[1] or b[1]] # sum, carry
+
+proc fa4(a,b): array[5, bool] =
+  var co,s: array[4, bool]
+  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): array[4, bool] =
+  var n = n
+  for i in 0..result.high:
+    result[i] = (n and 1) == 1
+    n = n shr 1
+
+proc bus2int(b): 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))