From ea5f0ce5529a855dd6bf2d99c39adce05dbc2539 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Mon, 17 Jan 2022 09:29:11 -0400
Subject: [PATCH] feat(cpu): implement some already decoded format 3
 instructions

---
 src/cpu/thumb/format3.zig | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/cpu/thumb/format3.zig b/src/cpu/thumb/format3.zig
index d759c7b..7939113 100644
--- a/src/cpu/thumb/format3.zig
+++ b/src/cpu/thumb/format3.zig
@@ -11,16 +11,33 @@ pub fn format3(comptime op: u2, comptime rd: u3) InstrFn {
 
             switch (op) {
                 0b00 => {
+                    // MOV
                     cpu.r[rd] = offset;
 
                     cpu.cpsr.n.unset();
                     cpu.cpsr.z.write(offset == 0);
                 },
                 0b01 => {
-                    std.debug.panic("TODO: Implement cmp R{}, #0x{X:0>2}", .{ rd, offset });
+                    // CMP
+                    const left = cpu.r[rd];
+                    const result = left -% offset;
+
+                    cpu.cpsr.n.write(result >> 31 & 1 == 1);
+                    cpu.cpsr.z.write(result == 0);
+                    cpu.cpsr.c.write(offset <= left);
+                    cpu.cpsr.v.write(((left ^ result) & (~offset ^ result)) >> 31 & 1 == 1);
                 },
                 0b10 => {
-                    std.debug.panic("TODO: Implement add R{}, #0x{X:0>2}", .{ rd, offset });
+                    const left = cpu.r[rd];
+
+                    var result: u32 = undefined;
+                    const didOverflow = @addWithOverflow(u32, left, offset, &result);
+                    cpu.r[rd] = result;
+
+                    cpu.cpsr.n.write(result >> 31 & 1 == 1);
+                    cpu.cpsr.z.write(result == 0);
+                    cpu.cpsr.c.write(didOverflow);
+                    cpu.cpsr.v.write(((left ^ result) & (offset ^ result)) >> 31 & 1 == 1);
                 },
                 0b11 => {
                     std.debug.panic("TODO: Implement sub R{}, #0x{X:0>2}", .{ rd, offset });