From 7d4dd52b8cfc865ae1b975ca3b6a3e72a812ebb9 Mon Sep 17 00:00:00 2001
From: Ben Bridle <bridle.benjamin@gmail.com>
Date: Fri, 14 Feb 2025 09:36:52 +1300
Subject: Rewrite library

---
 src/stages/bytecode.rs | 137 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 137 insertions(+)
 create mode 100644 src/stages/bytecode.rs

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

diff --git a/src/stages/bytecode.rs b/src/stages/bytecode.rs
new file mode 100644
index 0000000..db6ff6d
--- /dev/null
+++ b/src/stages/bytecode.rs
@@ -0,0 +1,137 @@
+use crate::*;
+
+use std::collections::HashMap;
+
+
+/// Doesn't truncate trailing null bytes.
+pub fn generate_bytecode(semantic: &Program) -> AssembledProgram {
+    let mut generator = BytecodeGenerator::new(&semantic.definitions);
+    generator.parse(&semantic.tokens, false);
+    generator.fill_slots();
+    let mut symbols = Vec::new();
+    for (name, information) in generator.labels {
+        let source = semantic.definitions.get(&name).unwrap().source.clone();
+        let address = information.address;
+        symbols.push(AssembledSymbol { name, address, source });
+    }
+    AssembledProgram {
+        bytecode: generator.bytecode,
+        symbols,
+    }
+}
+
+
+pub struct BytecodeGenerator<'a> {
+    definitions: &'a HashMap<String, Tracked<Definition>>,
+    labels: HashMap<String, LabelInformation>,
+    stack: Vec<usize>,
+    bytecode: Vec<u8>,
+}
+
+struct LabelInformation {
+    address: usize,
+    slots: Vec<usize>,
+}
+
+impl<'a> BytecodeGenerator<'a> {
+    pub fn new(definitions: &'a HashMap<String, Tracked<Definition>>) -> Self {
+        let mut labels = HashMap::new();
+        for (name, definition) in definitions {
+            if let DefinitionKind::LabelDefinition = definition.kind {
+                labels.insert(name, LabelInformation { address: 0, slots: Vec::new() });
+            }
+        }
+        Self {
+            definitions,
+            labels: HashMap::new(),
+            stack: Vec::new(),
+            bytecode: Vec::new(),
+        }
+    }
+
+    pub fn parse(&mut self, tokens: &[Tracked<SemanticToken>], in_macro: bool) {
+        macro_rules! byte {
+            ($byte:expr) => {
+                self.bytecode.push($byte)
+            };
+        }
+        macro_rules! double {
+            ($double:expr) => {{
+                let [high, low] = u16::to_be_bytes($double);
+                self.bytecode.push(high);
+                self.bytecode.push(low);
+            }};
+        }
+
+        for token in tokens {
+            let i = self.bytecode.len();
+            match &token.value {
+                SemanticToken::Comment(_) => (),
+
+                SemanticToken::LabelDefinition(name) => if in_macro {
+                    unreachable!("Uncaught label definition in macro");
+                } else {
+                    let information = self.labels.get_mut(name).unwrap();
+                    information.address = i;
+                }
+                SemanticToken::MacroDefinition{ .. } => if in_macro {
+                    unreachable!("Uncaught macro definition in macro");
+                }
+
+                SemanticToken::RawValue(value) => match value {
+                    Value::Byte(byte) => byte!(*byte),
+                    Value::Double(double) => double!(*double),
+                }
+                SemanticToken::Instruction(instruction) => {
+                    byte!(instruction.value)
+                }
+                SemanticToken::Invocation(name) => {
+                    if let Some(definition) = self.definitions.get(name) {
+                        match &definition.kind {
+                            DefinitionKind::MacroDefinition(body) => {
+                                self.parse(body, true);
+                            }
+                            DefinitionKind::LabelDefinition => {
+                                let information = self.labels.get_mut(name).unwrap();
+                                information.slots.push(i);
+                                double!(0);
+                            }
+                        }
+                    } else {
+                        unreachable!("Uncaught undefined symbol '{name}'");
+                    }
+                }
+
+                SemanticToken::Padding(value) => {
+                    self.bytecode.resize(i + usize::from(value), 0);
+                },
+                SemanticToken::String(bytes) => {
+                    self.bytecode.extend_from_slice(bytes)
+                },
+
+                SemanticToken::BlockOpen(_) => {
+                    self.stack.push(i);
+                    double!(0);
+                }
+                SemanticToken::BlockClose(_) => {
+                    let Some(addr) = self.stack.pop() else {
+                        unreachable!("Uncaught unmatched block terminator");
+                    };
+                    let [high, low] = (addr as u16).to_be_bytes();
+                    self.bytecode[addr] = high;
+                    self.bytecode[addr+1] = low;
+                }
+            }
+        }
+    }
+
+    pub fn fill_slots(&mut self) {
+        for information in self.labels.values() {
+            let [high, low] = (information.address as u16).to_be_bytes();
+            for addr in &information.slots {
+                self.bytecode[*addr] = high;
+                self.bytecode[*addr + 1] = low;
+            }
+        }
+    }
+}
-- 
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