alu bugfix

cpu/alu/adder16.sv

@@ -9,7 +9,7 @@ package adder16 (
     wire [15:0]c
 );
 
-lookahead(c, a, b);
+c = 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]);

cpu/alu/alu.sv

@@ -19,7 +19,7 @@ assign nb = sel[3];    // if nx=1, b=!b
 assign f  = sel[4];  // if f=0 -> a&b; else -> a+b
 assign no = sel[5];  // if no=1, out=!out
 
-wire [15:0]zero16 = 0;
+wire [15:0] zero16 = 15'b0000000000000000;
 
 always @(*) begin
 
@@ -47,10 +47,10 @@ always @(*) begin
         alu_out = tmpOut;
     end
 
-    if (alu_out == 0)
-        flag = 0;   // zero flag
-    else if (alu_out < 0)
-        flag = 1;   // negative flag
+    if (alu_out < 0)
+        flag = 0;   // negative flag
+    else if (alu_out = 0)
+        flag = 1;   // zero flag
     else if
         flag = 2   // positive flag
     end