feat(cpu): implement THUMB format 5 instructions

src/cpu/thumb/format5.zig

@@ -0,0 +1,35 @@
+const std = @import("std");
+
+const Bus = @import("../../Bus.zig");
+const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
+const InstrFn = @import("../../cpu.zig").ThumbInstrFn;
+
+pub fn format5(comptime op: u2, comptime h1: u1, comptime h2: u1) InstrFn {
+    return struct {
+        fn inner(cpu: *Arm7tdmi, _: *Bus, opcode: u16) void {
+            const src = @as(u4, h2) << 3 | (opcode >> 3 & 0x7);
+            const dst = @as(u4, h1) << 3 | (opcode & 0x7);
+
+            switch (op) {
+                0b01 => {
+                    // CMP
+                    const left = cpu.r[dst];
+                    const right = cpu.r[src];
+                    const result = left -% right;
+
+                    cpu.cpsr.n.write(result >> 31 & 1 == 1);
+                    cpu.cpsr.z.write(result == 0);
+                    cpu.cpsr.c.write(right <= left);
+                    cpu.cpsr.v.write(((left ^ result) & (~right ^ result)) >> 31 & 1 == 1);
+                },
+                0b10 => cpu.r[dst] = cpu.r[src], // MOV
+                0b11 => {
+                    // BX
+                    cpu.cpsr.t.write(cpu.r[src] & 1 == 1);
+                    cpu.r[15] = cpu.r[src] & 0xFFFF_FFFE;
+                },
+                else => std.debug.panic("[CPU] Op #{} is invalid for THUMB Format 5", .{op}),
+            }
+        }
+    }.inner;
+}