From 9a6ccf6d480d53a95181c959388a4f01a3a8e413 Mon Sep 17 00:00:00 2001
From: Nick Krichevsky <nick@ollien.com>
Date: Sat, 18 Nov 2023 10:02:51 -0500
Subject: [PATCH] Simplify load8 parsing to use bitwise ops

---
 src/cpu/parse/load8/transfer.rs | 92 +++++++++++----------------------
 1 file changed, 30 insertions(+), 62 deletions(-)

diff --git a/src/cpu/parse/load8/transfer.rs b/src/cpu/parse/load8/transfer.rs
index 383a09b..d341cb7 100644
--- a/src/cpu/parse/load8/transfer.rs
+++ b/src/cpu/parse/load8/transfer.rs
@@ -13,71 +13,39 @@ pub struct Parser;
 impl OpcodeParser for Parser {
     /// Parses an opcode that transfers an 8bit values between single 8 bit registers.
     fn parse_opcode(data: &View) -> ParseResult {
-        // I don't normally like doing this but this function was ridiculous with the line length wrapping
-        // caused by not doing it
-        #[allow(clippy::enum_glob_use)]
-        use register::SingleEightBit::*;
-
         let opcode = parse::get_opcode_from_data(data);
-        match opcode {
-            0x7f => Ok(make_load_between_register_data(A, A)),
-            0x78 => Ok(make_load_between_register_data(A, B)),
-            0x79 => Ok(make_load_between_register_data(A, C)),
-            0x7A => Ok(make_load_between_register_data(A, D)),
-            0x7B => Ok(make_load_between_register_data(A, E)),
-            0x7C => Ok(make_load_between_register_data(A, H)),
-            0x7D => Ok(make_load_between_register_data(A, L)),
+        let dst = parse_destination_register(opcode)?;
+        let src = parse_source_register(opcode)?;
 
-            0x47 => Ok(make_load_between_register_data(B, A)),
-            0x40 => Ok(make_load_between_register_data(B, B)),
-            0x41 => Ok(make_load_between_register_data(B, C)),
-            0x42 => Ok(make_load_between_register_data(B, D)),
-            0x43 => Ok(make_load_between_register_data(B, E)),
-            0x44 => Ok(make_load_between_register_data(B, H)),
-            0x45 => Ok(make_load_between_register_data(B, L)),
+        Ok(make_load_between_register_data(dst, src))
+    }
+}
+fn parse_destination_register(opcode: u8) -> Result<register::SingleEightBit, parse::Error> {
+    let source_part = opcode & 0xF0;
+    let offset = opcode & 0x0F;
+    match source_part {
+        0x40 if offset <= 7 => Ok(register::SingleEightBit::B),
+        0x40 if offset > 7 => Ok(register::SingleEightBit::C),
+        0x50 if offset <= 7 => Ok(register::SingleEightBit::D),
+        0x50 if offset > 7 => Ok(register::SingleEightBit::E),
+        0x60 if offset <= 7 => Ok(register::SingleEightBit::H),
+        0x60 if offset > 7 => Ok(register::SingleEightBit::L),
+        0x70 if offset > 7 => Ok(register::SingleEightBit::A),
+        _ => Err(Error::UnknownOpcode(opcode))
+    }
+}
 
-            0x4F => Ok(make_load_between_register_data(C, A)),
-            0x48 => Ok(make_load_between_register_data(C, B)),
-            0x49 => Ok(make_load_between_register_data(C, C)),
-            0x4A => Ok(make_load_between_register_data(C, D)),
-            0x4B => Ok(make_load_between_register_data(C, E)),
-            0x4C => Ok(make_load_between_register_data(C, H)),
-            0x4D => Ok(make_load_between_register_data(C, L)),
-
-            0x57 => Ok(make_load_between_register_data(D, A)),
-            0x50 => Ok(make_load_between_register_data(D, B)),
-            0x51 => Ok(make_load_between_register_data(D, C)),
-            0x52 => Ok(make_load_between_register_data(D, D)),
-            0x53 => Ok(make_load_between_register_data(D, E)),
-            0x54 => Ok(make_load_between_register_data(D, H)),
-            0x55 => Ok(make_load_between_register_data(D, L)),
-
-            0x5F => Ok(make_load_between_register_data(E, A)),
-            0x58 => Ok(make_load_between_register_data(E, B)),
-            0x59 => Ok(make_load_between_register_data(E, C)),
-            0x5A => Ok(make_load_between_register_data(E, D)),
-            0x5B => Ok(make_load_between_register_data(E, E)),
-            0x5C => Ok(make_load_between_register_data(E, H)),
-            0x5D => Ok(make_load_between_register_data(E, L)),
-
-            0x67 => Ok(make_load_between_register_data(H, A)),
-            0x60 => Ok(make_load_between_register_data(H, B)),
-            0x61 => Ok(make_load_between_register_data(H, C)),
-            0x62 => Ok(make_load_between_register_data(H, D)),
-            0x63 => Ok(make_load_between_register_data(H, E)),
-            0x64 => Ok(make_load_between_register_data(H, H)),
-            0x65 => Ok(make_load_between_register_data(H, L)),
-
-            0x6F => Ok(make_load_between_register_data(L, A)),
-            0x68 => Ok(make_load_between_register_data(L, B)),
-            0x69 => Ok(make_load_between_register_data(L, C)),
-            0x6A => Ok(make_load_between_register_data(L, D)),
-            0x6B => Ok(make_load_between_register_data(L, E)),
-            0x6c => Ok(make_load_between_register_data(L, H)),
-            0x6D => Ok(make_load_between_register_data(L, L)),
-
-            _ => Err(Error::UnknownOpcode(opcode)),
-        }
+fn parse_source_register(opcode: u8) -> Result<register::SingleEightBit, parse::Error> {
+    let offset = opcode & 0x07;
+    match offset {
+        0x00 => Ok(register::SingleEightBit::B),
+        0x01 => Ok(register::SingleEightBit::C),
+        0x02 => Ok(register::SingleEightBit::D),
+        0x03 => Ok(register::SingleEightBit::E),
+        0x04 => Ok(register::SingleEightBit::H),
+        0x05 => Ok(register::SingleEightBit::L),
+        0x07 => Ok(register::SingleEightBit::A),
+        _ => Err(Error::UnknownOpcode(opcode))
     }
 }