chore(cpu): refactor ARM functions to make room for THUMB

src/cpu/arm/psr_transfer.zig

@@ -0,0 +1,51 @@
+const std = @import("std");
+
+const Bus = @import("../../Bus.zig");
+const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
+const InstrFn = @import("../../cpu.zig").InstrFn;
+
+pub fn psrTransfer(comptime I: bool, comptime isSpsr: bool) InstrFn {
+    return struct {
+        fn inner(cpu: *Arm7tdmi, _: *Bus, opcode: u32) void {
+            switch (@truncate(u3, opcode >> 19)) {
+                0b001 => {
+                    // MRS
+                    const rn = opcode >> 12 & 0xF;
+
+                    if (isSpsr) {
+                        std.debug.panic("[CPU] TODO: MRS on SPSR_<current_mode> is unimplemented", .{});
+                    } else {
+                        cpu.r[rn] = cpu.cpsr.raw;
+                    }
+                },
+                0b101 => {
+                    // MSR
+                    const rm = opcode & 0xF;
+
+                    switch (@truncate(u3, opcode >> 16)) {
+                        0b000 => {
+                            const right = if (I) std.math.rotr(u32, opcode & 0xFF, opcode >> 7 & 0xF) else cpu.r[rm];
+
+                            if (isSpsr) {
+                                std.debug.panic("[CPU] TODO: MSR (flags only) on SPSR_<current_mode> is unimplemented", .{});
+                            } else {
+                                const mask: u32 = 0xF000_0000;
+                                cpu.cpsr.raw = (cpu.cpsr.raw & ~mask) | (right & mask);
+                            }
+                        },
+                        0b001 => {
+                            if (isSpsr) {
+                                std.debug.panic("[CPU] TODO: MSR on SPSR_<current_mode> is unimplemented", .{});
+                            } else {
+                                cpu.cpsr = .{ .raw = cpu.r[rm] };
+                            }
+                        },
+
+                        else => unreachable,
+                    }
+                },
+                else => unreachable,
+            }
+        }
+    }.inner;
+}