feat(cpu): implement ARM SWP and SWPB

src/cpu/arm/single_data_swap.zig

@@ -0,0 +1,29 @@
+const std = @import("std");
+
+const Bus = @import("../../Bus.zig");
+const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
+const InstrFn = @import("../../cpu.zig").ArmInstrFn;
+
+pub fn singleDataSwap(comptime B: bool) InstrFn {
+    return struct {
+        fn inner(cpu: *Arm7tdmi, bus: *Bus, opcode: u32) void {
+            const rn = opcode >> 16 & 0xF;
+            const rd = opcode >> 12 & 0xF;
+            const rm = opcode & 0xF;
+
+            const address = cpu.r[rn];
+
+            if (B) {
+                // SWPB
+                const value = bus.read8(address);
+                bus.write8(address, @truncate(u8, cpu.r[rm]));
+                cpu.r[rd] = value;
+            } else {
+                // SWP
+                const value = std.math.rotr(u32, bus.read32(address), 8 * (address & 0x3));
+                bus.write32(address, cpu.r[rm]);
+                cpu.r[rd] = value;
+            }
+        }
+    }.inner;
+}