feat(cpu): implement format 1 THUMB instructions

src/cpu/thumb/format1.zig

@@ -0,0 +1,28 @@
+const std = @import("std");
+
+const Bus = @import("../../Bus.zig");
+const Arm7tdmi = @import("../../cpu.zig").Arm7tdmi;
+const InstrFn = @import("../../cpu.zig").ThumbInstrFn;
+const shifter = @import("../arm/barrel_shifter.zig");
+
+pub fn format1(comptime op: u2, comptime offset: u5) InstrFn {
+    return struct {
+        fn inner(cpu: *Arm7tdmi, _: *Bus, opcode: u16) void {
+            const rs = opcode >> 3 & 0x7;
+            const rd = opcode & 0x7;
+
+            const result = switch (op) {
+                0b00 => shifter.logicalLeft(true, &cpu.cpsr, cpu.r[rs], offset),
+                0b01 => shifter.logicalRight(true, &cpu.cpsr, cpu.r[rs], offset),
+                0b10 => shifter.arithmeticRight(true, &cpu.cpsr, cpu.r[rs], offset),
+                else => std.debug.panic("{} is an invalid op for Format 1 THUMB Instructions", .{op}),
+            };
+
+            cpu.r[rd] = result;
+
+            // Instructions of this type are equivalent to a MOVS
+            cpu.cpsr.n.write(result >> 31 & 1 == 1);
+            cpu.cpsr.z.write(result == 0);
+        }
+    }.inner;
+}