feat(cpu): implement like 1 THUMB instruction

src/cpu/thumb/format3.zig

@@ -0,0 +1,32 @@
+const std = @import("std");
+
+const Bus = @import("../../Bus.zig");
+const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
+const InstrFn = @import("../../cpu.zig").ThumbInstrFn;
+
+pub fn format3(comptime op: u2, comptime rd: u3) InstrFn {
+    return struct {
+        fn inner(cpu: *Arm7tdmi, _: *Bus, opcode: u16) void {
+            const offset = @truncate(u8, opcode);
+
+            switch (op) {
+                0b00 => {
+                    cpu.r[rd] = offset;
+
+                    cpu.cpsr.n.unset();
+                    cpu.cpsr.z.write(offset == 0);
+                    std.debug.panic("TODO: Implement mov R{}, #0x{X:0>2}", .{ rd, offset });
+                },
+                0b01 => {
+                    std.debug.panic("TODO: Implement cmp R{}, #0x{X:0>2}", .{ rd, offset });
+                },
+                0b10 => {
+                    std.debug.panic("TODO: Implement add R{}, #0x{X:0>2}", .{ rd, offset });
+                },
+                0b11 => {
+                    std.debug.panic("TODO: Implement sub R{}, #0x{X:0>2}", .{ rd, offset });
+                },
+            }
+        }
+    }.inner;
+}