performance optimizations

added carry lookahead pakage used inside adder16

cpu/alu/adder16.sv

@@ -1,4 +1,5 @@
 import adder::*;
+import lookahead::*;
 
 package adder16 (
     output [15:0]sum16,
@@ -8,21 +9,23 @@ package adder16 (
     wire [15:0]c
 );
 
-adder(sum16[0], carry16[0], a16[0], b16[0], c[0] = 0);
-adder(sum16[1], carry16[1], a16[1], b16[1], c[1] = carry16[0]);
-adder(sum16[2], carry16[2], a16[2], b16[2], c[2] = carry16[1]);
-adder(sum16[3], carry16[3], a16[3], b16[3], c[3] = carry16[2]);
-adder(sum16[4], carry16[4], a16[4], b16[4], c[4] = carry16[3]);
-adder(sum16[5], carry16[5], a16[5], b16[5], c[5] = carry16[4]);
-adder(sum16[6], carry16[6], a16[6], b16[6], c[6] = carry16[5]);
-adder(sum16[7], carry16[7], a16[7], b16[7], c[7] = carry16[6]);
-adder(sum16[8], carry16[8], a16[8], b16[8], c[8] = carry16[7]);
-adder(sum16[9], carry16[9], a16[9], b16[9], c[9] = carry16[8]);
-adder(sum16[10], carry16[10], a16[10], b16[10], c[10] = carry16[9]);
-adder(sum16[11], carry16[11], a16[11], b16[11], c[11] = carry16[10]);
-adder(sum16[12], carry16[12], a16[12], b16[12], c[12] = carry16[11]);
-adder(sum16[13], carry16[13], a16[13], b16[13], c[13] = carry16[12]);
-adder(sum16[14], carry16[14], a16[14], b16[14], c[14] = carry16[13]);
-adder(sum16[15], carry16[15], a16[15], b16[15], c[15] = carry16[14]);
+lookahead(c, a, b);
+
+adder(sum16[0], carry16[0] = c[0], a16[0], b16[0],);
+adder(sum16[1], carry16[1] = c[1], a16[1], b16[1]);
+adder(sum16[2], carry16[2] = c[2], a16[2], b16[2]);
+adder(sum16[3], carry16[3] = c[3], a16[3], b16[3]);
+adder(sum16[4], carry16[4] = c[4], a16[4], b16[4]);
+adder(sum16[5], carry16[5] = c[5], a16[5], b16[5]);
+adder(sum16[6], carry16[6] = c[6], a16[6], b16[6]);
+adder(sum16[7], carry16[7] = c[7], a16[7], b16[7]);
+adder(sum16[8], carry16[8] = c[8], a16[8], b16[8]);
+adder(sum16[9], carry16[9] = c[9], a16[9], b16[9]);
+adder(sum16[10], carry16[10] = c[10], a16[10], b16[10]);
+adder(sum16[11], carry16[11] = c[11], a16[11], b16[11]);
+adder(sum16[12], carry16[12] = c[12], a16[12], b16[12]);
+adder(sum16[13], carry16[13] = c[13], a16[13], b16[13]);
+adder(sum16[14], carry16[14] = c[14], a16[14], b16[14]);
+adder(sum16[15], carry16[15] = c[15], a16[15], b16[15]);
 
 endpackage

cpu/alu/lookahead.sv

@@ -0,0 +1,17 @@
+package lookahead (
+    output [15:0]carry_bit,
+    input [15:0]a,
+    input [15:0]b,
+);
+
+    res = and16(y, a, b);
+
+    for (i=0; i<15 ; i=i+1)
+        if (res[i] = 0)
+            carry_bit[i] = 0;
+        else
+            carry_bit[i] = 1;
+        end
+    end
+
+endpackage