feat(cpu): implement format2 THUMB instructions

src/cpu/thumb/format2.zig

@@ -0,0 +1,33 @@
+const std = @import("std");
+
+const Bus = @import("../../Bus.zig");
+const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
+const InstrFn = @import("../../cpu.zig").ThumbInstrFn;
+
+const add = @import("../arm/data_processing.zig").add;
+const sub = @import("../arm/data_processing.zig").sub;
+
+pub fn format2(comptime I: bool, is_sub: bool, rn: u3) InstrFn {
+    return struct {
+        fn inner(cpu: *Arm7tdmi, _: *Bus, opcode: u16) void {
+            const rs = opcode >> 3 & 0x7;
+            const rd = @truncate(u3, opcode);
+
+            if (is_sub) {
+                // SUB
+                cpu.r[rd] = if (I) blk: {
+                    break :blk sub(true, cpu, rd, cpu.r[rs], @as(u32, rn));
+                } else blk: {
+                    break :blk sub(true, cpu, rd, cpu.r[rs], cpu.r[rn]);
+                };
+            } else {
+                // ADD
+                cpu.r[rd] = if (I) blk: {
+                    break :blk add(true, cpu, rd, cpu.r[rs], @as(u32, rn));
+                } else blk: {
+                    break :blk add(true, cpu, rd, cpu.r[rs], cpu.r[rn]);
+                };
+            }
+        }
+    }.inner;
+}