emux64: cpu: Add emulation of SUB instruction

Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/emux64/src/cpu/cpu_cycle.c b/emux64/src/cpu/cpu_cycle.c
index b3a8987..663b300 100644
--- a/emux64/src/cpu/cpu_cycle.c
+++ b/emux64/src/cpu/cpu_cycle.c
@@ -207,6 +207,21 @@ cpu_do_add(struct osmx_core *core)
 
 }
 
+static int
+cpu_do_sub(struct osmx_core *core)
+{
+    struct arithop ops;
+    int error;
+
+    error = cpu_arithop(core, &ops);
+    if (error < 0) {
+        return error;
+    }
+
+    core->xn[ops.dest_reg] = ops.op1 - ops.op2;
+    return 0;
+}
+
 int
 cpu_run(struct osmx_core *core)
 {
@@ -240,6 +255,12 @@ cpu_run(struct osmx_core *core)
                 continue;
             }
             break;
+        case OP_SUB:
+            if (cpu_do_sub(core) < 0) {
+                core->run = false;
+                continue;
+            }
+            break;
         case OP_NOP:
             break;
         default: