feat(cpu): implement format16 THUMB instructions

src/cpu/thumb/format16.zig

@@ -0,0 +1,22 @@
+const std = @import("std");
+
+const Bus = @import("../../Bus.zig");
+const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
+const InstrFn = @import("../../cpu.zig").ThumbInstrFn;
+const checkCond = @import("../../cpu.zig").checkCond;
+const u32SignExtend = @import("../../util.zig").u32SignExtend;
+
+pub fn format16(comptime cond: u4) InstrFn {
+    return struct {
+        fn inner(cpu: *Arm7tdmi, _: *Bus, opcode: u16) void {
+            const offset = (opcode & 0xFF) << 1;
+
+            const do_execute = switch (cond) {
+                0xE, 0xF => std.debug.panic("[CPU/THUMB] Undefined conditional branch with condition {}", .{cond}),
+                else => checkCond(cpu.cpsr, cond),
+            };
+
+            if (do_execute) cpu.r[15] = (cpu.fakePC() & 0xFFFF_FFFC) +% u32SignExtend(8, offset);
+        }
+    }.inner;
+}