From ef13c43912c88d3e238ef834d1882c1b0ada8f44 Mon Sep 17 00:00:00 2001
From: Nate Catelli <ncatelli@packetfire.org>
Date: Fri, 25 Aug 2023 19:50:31 +0000
Subject: [PATCH] feat(chip8): replace parcel with bit decoder

BREAKING CHANGE: Calls to OpcodeVariantParser.parse will no longer be available.
---
 Cargo.toml                            |  3 ---
 src/cpu/chip8/mod.rs                  | 20 ++++------------
 src/cpu/chip8/operations/mod.rs       | 33 +++++++++++----------------
 src/cpu/chip8/operations/tests/mod.rs | 11 +++------
 4 files changed, 20 insertions(+), 47 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 426a269..37d9473 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -4,9 +4,6 @@ version = "0.2.2"
 authors = ["Nate Catelli <ncatelli@packetfire.org>"]
 edition = "2021"
 
-[dependencies]
-parcel = { git = "https://github.com/ncatelli/parcel", tag = "v2.0.1" }
-
 [dependencies.isa-mos6502]
 git = "https://github.com/ncatelli/isa-mos6502"
 tag = "v1.1.0"
diff --git a/src/cpu/chip8/mod.rs b/src/cpu/chip8/mod.rs
index 1965a68..34eb852 100644
--- a/src/cpu/chip8/mod.rs
+++ b/src/cpu/chip8/mod.rs
@@ -1,7 +1,6 @@
 use crate::address_map::{AddressMap, Addressable};
 use crate::cpu::Execute;
 use crate::cpu::{register::Register, Cpu, StepState};
-use parcel::Parser;
 
 use super::ExecuteMut;
 
@@ -339,24 +338,13 @@ where
     fn next(&mut self) -> Option<Vec<microcode::Microcode>> {
         use crate::cpu::Generate;
         let pc = self.state.pc.read();
-        let opcodes: [(usize, u8); 2] = [
-            (pc as usize, self.state.address_space.read(pc)),
-            ((pc as usize + 1), self.state.address_space.read(pc + 1)),
+        let opcodes: [u8; 2] = [
+            self.state.address_space.read(pc),
+            self.state.address_space.read(pc + 1),
         ];
 
         // Parse correct operation
-        let ops = match operations::OpcodeVariantParser.parse(&opcodes[..]) {
-            Ok(parcel::MatchStatus::Match {
-                span: _,
-                remainder: _,
-                inner: op,
-            }) => Ok(op),
-            _ => Err(format!(
-                "No match found for {:#02x}",
-                u16::from_be_bytes([opcodes[0].1, opcodes[1].1])
-            )),
-        }
-        .unwrap();
+        let ops = operations::decode_bytes_to_opcode(opcodes).unwrap();
 
         let microcode_steps: Vec<microcode::Microcode> = ops
             .generate(&self.state)
diff --git a/src/cpu/chip8/operations/mod.rs b/src/cpu/chip8/operations/mod.rs
index 6277199..84de6ba 100644
--- a/src/cpu/chip8/operations/mod.rs
+++ b/src/cpu/chip8/operations/mod.rs
@@ -8,7 +8,6 @@ use crate::cpu::chip8::{
 };
 use crate::cpu::Generate;
 use crate::prelude::v1::Register;
-use parcel::prelude::v1::*;
 use std::convert::TryFrom;
 
 pub mod addressing_mode;
@@ -175,13 +174,13 @@ where
     }
 }
 
-/// Provides a Parser type for the OpcodeVariant enum. Constructing an
-/// OpcodeVariant from a stream of bytes.
-pub struct OpcodeVariantParser;
+pub(crate) fn decode_bytes_to_opcode(bytes: impl AsRef<[u8]>) -> Result<Opcode, String> {
+    let bin_data = bytes.as_ref();
 
-impl<'a> Parser<'a, &'a [(usize, u8)], Opcode> for OpcodeVariantParser {
-    fn parse(&self, input: &'a [(usize, u8)]) -> parcel::ParseResult<&'a [(usize, u8)], Opcode> {
-        let ms = input.get(0..2).map(|v| [v[0].1, v[1].1]).and_then(|bytes| {
+    bin_data
+        .get(0..2)
+        .map(|v| [v[0], v[1]])
+        .and_then(|bytes| {
             let [[first, second], [third, fourth]] =
                 [u8::to_be_nibbles(&bytes[0]), u8::to_be_nibbles(&bytes[1])];
             let dest_reg: GpRegisters =
@@ -229,19 +228,13 @@ impl<'a> Parser<'a, &'a [(usize, u8)], Opcode> for OpcodeVariantParser {
                 [0xf, _, 0x6, 0x5] => Some(Opcode::ReadRegistersFromMemory(dest_reg)),
                 _ => None,
             }
-        });
-
-        // if we get a match, set the appropiate match status headers.
-        match ms {
-            Some(op) => Ok(MatchStatus::Match {
-                /// increment end span to cover non-inclusivity.
-                span: input[0].0..(input[1].0 + 1),
-                inner: op,
-                remainder: &input[2..],
-            }),
-            None => Ok(MatchStatus::NoMatch(input)),
-        }
-    }
+        })
+        .ok_or_else(|| {
+            format!(
+                "No match found for {:#02x}",
+                u16::from_be_bytes([bin_data[0], bin_data[1]])
+            )
+        })
 }
 
 /// Clear the display.
diff --git a/src/cpu/chip8/operations/tests/mod.rs b/src/cpu/chip8/operations/tests/mod.rs
index d006a14..abeea98 100644
--- a/src/cpu/chip8/operations/tests/mod.rs
+++ b/src/cpu/chip8/operations/tests/mod.rs
@@ -7,19 +7,14 @@ macro_rules! generate_parse_test {
         $(
         #[test]
         fn $testname() {
-            let input: Vec<(usize, u8)> = $input_bytes
+            let input: Vec<u8> = $input_bytes
                 .to_be_bytes()
                 .iter()
                 .copied()
-                .enumerate()
                 .collect();
             assert_eq!(
-                Ok(MatchStatus::Match {
-                    span: 0..2,
-                    remainder: &input[2..],
-                    inner: $variant,
-                }),
-                OpcodeVariantParser.parse(&input[..])
+                Ok($variant),
+                decode_bytes_to_opcode(&input[..])
             );
         }
         )*