September 2017 Update

Task/Four-bit-adder/Phix/four-bit-adder.phix

@@ -0,0 +1,47 @@
+function xor_gate(bool a, bool b)
+    return (a and not b) or (not a and b)
+end function
+
+function half_adder(bool a, bool b)
+    bool s = xor_gate(a,b)
+    bool c = a and b
+    return {s,c}
+end function
+
+function full_adder(bool a, bool b, bool c)
+    bool {s1,c1} = half_adder(c,a)
+    bool {s2,c2} = half_adder(s1,b)
+    c = c1 or c2
+    return {s2,c}
+end function
+
+function four_bit_adder(bool a0, a1, a2, a3, b0, b1, b2, b3)
+bool s0,s1,s2,s3,c
+    {s0,c} = full_adder(a0,b0,0)
+    {s1,c} = full_adder(a1,b1,c)
+    {s2,c} = full_adder(a2,b2,c)
+    {s3,c} = full_adder(a3,b3,c)
+    return {s3,s2,s1,s0,c}
+end function
+
+procedure test(integer a, integer b)
+    bool {a0,a1,a2,a3} = int_to_bits(a,4)
+    bool {b0,b1,b2,b3} = int_to_bits(b,4)
+    bool {r3,r2,r1,r0,c} = four_bit_adder(a0,a1,a2,a3,b0,b1,b2,b3)
+    integer r = bits_to_int({r0,r1,r2,r3})
+    printf(1,"%04b + %04b = %04b %b (%d+%d=%d)\n",{a,b,r,c,a,b,c*16+r})
+end procedure
+
+test(0,0)
+test(0,1)
+test(0b1111,0b1111)
+test(3,7)
+test(11,8)
+test(0b1100,0b1100)
+test(0b1100,0b1101)
+test(0b1100,0b1110)
+test(0b1100,0b1111)
+test(0b1101,0b0000)
+test(0b1101,0b0001)
+test(0b1101,0b0010)
+test(0b1101,0b0011)