From 17face3633686e374aa0859271ccf462a48e60aa Mon Sep 17 00:00:00 2001
From: Rose Hogenson <rosehogenson@posteo.net>
Date: Sun, 4 Feb 2024 16:46:20 -0800
Subject: Rewrite the bytecode interpreter in Rust.

---
 bytecode/src/encoding.rs | 139 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 139 insertions(+)
 create mode 100644 bytecode/src/encoding.rs

(limited to 'bytecode/src/encoding.rs')

diff --git a/bytecode/src/encoding.rs b/bytecode/src/encoding.rs
new file mode 100644
index 0000000..e37696d
--- /dev/null
+++ b/bytecode/src/encoding.rs
@@ -0,0 +1,139 @@
+use crate::heap;
+use crate::value::Value;
+use std::error::Error;
+
+pub enum Arg {
+    Local(u8),
+    Const(Value),
+}
+
+pub struct Alloc {
+    pub out: u8,
+    pub size: Arg,
+}
+
+pub struct Poke {
+    pub offset: usize,
+    pub ptr: u8,
+    pub val: Arg,
+}
+
+pub struct Peek {
+    pub out: u8,
+    pub offset: usize,
+    pub val: Arg,
+}
+
+pub struct Shuf {
+    pub out: u8,
+    pub val: Arg,
+}
+
+pub struct Exit {
+    pub val: Arg,
+}
+
+pub enum Op {
+    Alloc(Alloc),
+    Call,
+    Poke(Poke),
+    Peek(Peek),
+    Shuf(Shuf),
+    Exit(Exit),
+}
+
+struct Reader<'a> {
+    data: &'a [u8],
+    n: usize,
+}
+
+impl Reader<'_> {
+    fn advance(&mut self, size: usize) {
+        self.data = &self.data[size..];
+        self.n += size;
+    }
+
+    fn parse_byte(&mut self) -> Result<u8, Box<dyn Error>> {
+        if self.data.is_empty() {
+            return Err(Box::from("read byte: no data"));
+        }
+        let res = self.data[0];
+        self.advance(1);
+        Ok(res)
+    }
+
+    fn parse_local(&mut self) -> Result<u8, Box<dyn Error>> {
+        if self.data.is_empty() {
+            return Err(Box::from("local: no data"));
+        }
+        let res = self.data[0];
+        if usize::from(res) >= heap::NUM_LOCALS {
+            return Err(Box::from(format!("invalid local (out of range): {}", res)));
+        }
+        self.advance(1);
+        Ok(res)
+    }
+
+    fn parse_u64(&mut self) -> Result<u64, Box<dyn Error>> {
+        if self.data.len() < 8 {
+            return Err(Box::from("value: no data"));
+        }
+        let mut res = [0; 8];
+        res.copy_from_slice(&self.data[..8]);
+        self.advance(8);
+        Ok(u64::from_le_bytes(res))
+    }
+
+    fn parse_arg(&mut self, is_const: bool) -> Result<Arg, Box<dyn Error>> {
+        if is_const {
+            Ok(Arg::Const(Value(self.parse_u64()?)))
+        } else {
+            Ok(Arg::Local(self.parse_local()?))
+        }
+    }
+}
+
+impl Op {
+    pub fn parse(data: &[u8]) -> Result<(usize, Op), Box<dyn Error>> {
+        let mut r = Reader { data, n: 0 };
+        let code_byte = r.parse_byte()?;
+        let code = code_byte >> 2;
+        let arg1_const = code_byte & 2 != 0;
+        // let arg2_const = code_byte & 1 != 0;
+
+        let op = match code {
+            1 => {
+                let out = r.parse_local()?;
+                let size = r.parse_arg(arg1_const)?;
+                Op::Alloc(Alloc { out, size })
+            }
+            2 => Op::Call,
+            3 => {
+                let offset = usize::try_from(r.parse_u64()?)?;
+                let ptr = r.parse_local()?;
+                let val = r.parse_arg(arg1_const)?;
+                Op::Poke(Poke { offset, ptr, val })
+            }
+            4 => {
+                let out = r.parse_local()?;
+                let offset = usize::try_from(r.parse_u64()?)?;
+                let val = r.parse_arg(arg1_const)?;
+                Op::Peek(Peek { out, offset, val })
+            }
+            5 => {
+                let out = r.parse_local()?;
+                let val = r.parse_arg(arg1_const)?;
+                Op::Shuf(Shuf { out, val })
+            }
+            6 => {
+                let val = r.parse_arg(arg1_const)?;
+                Op::Exit(Exit { val })
+            }
+            _ => {
+                return Err(Box::from(format!("invalid code {}", code)));
+            }
+        };
+
+        Ok((r.n, op))
+    }
+}
-- 
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