From 261ae8eadc8a910b05d9d2b73b5be1272be7a26c Mon Sep 17 00:00:00 2001
From: uvok
Date: Fri, 16 Jan 2026 15:00:51 +0100
Subject: eater_alu: Use 2complneg instead of  subtract

---
 eater_cpu/eater_alu.sv | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

(limited to 'eater_cpu/eater_alu.sv')

diff --git a/eater_cpu/eater_alu.sv b/eater_cpu/eater_alu.sv
index b0fa9ae..01b62ae 100644
--- a/eater_cpu/eater_alu.sv
+++ b/eater_cpu/eater_alu.sv
@@ -6,12 +6,19 @@ module eater_alu (
     input clk_in,
     input en_output_in,
 
+    input subtract_n_add_in,
+
     input [7:0] A_in,
     input [7:0] B_in,
 
     output [7:0] bus_out
 );
 
-assign bus_out = en_output_in ? 0 : 8'bz;
+// wire [7:0] result = subtract_n_add_in ? (A_in - B_in) : (A_in + B_in);
+wire [7:0] xormask = {8{subtract_n_add_in}};
+wire [7:0] B_neg_if = B_in ^ xormask;
+wire [7:0] result2 = A_in + B_neg_if + subtract_n_add_in;
+
+assign bus_out = en_output_in ? result2 : 8'bz;
     
 endmodule
-- 
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