Initial instruction execution code i guess

Cargo.lock

@@ -17,9 +17,16 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "once_cell"
+version = "1.21.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "42f5e15c9953c5e4ccceeb2e7382a716482c34515315f7b03532b8b4e8393d2d"
+
 [[package]]
 name = "rvem"
 version = "0.1.0"
 dependencies = [
  "memmap2",
+ "once_cell",
 ]

Cargo.toml

@@ -5,3 +5,4 @@ edition = "2024"
 
 [dependencies]
 memmap2 = "0.9.8"
+once_cell = "1.21.3"

src/instructions.rs

@@ -0,0 +1,69 @@
+use once_cell::sync::Lazy;
+
+static INSTRUCTIONS: Lazy<[Option<OpcodeHandler>; 32]> = Lazy::new(|| {
+    let mut instructions = std::array::from_fn(|_i| None);
+
+    instructions
+});
+
+use crate::{consts::Word, core::Core, decode::Instruction};
+
+type Runner = fn(&mut Core, Instruction) -> Result<(), ()>;
+
+#[derive(Clone, Copy)]
+struct InstructionHandler {
+    runner: Runner,
+}
+
+struct OpcodeHandler {
+    handler: Option<InstructionHandler>,
+    splitter: Option<Splitter>,
+}
+
+pub fn find_runner(instruction: Instruction) -> Option<Runner> {
+    let opcode_handler = &INSTRUCTIONS[instruction.opcode_noncompressed() as usize];
+    match opcode_handler {
+        Some(h) => h.find_runner(instruction),
+        None => None,
+    }
+}
+
+impl OpcodeHandler {
+    fn find_runner(&self, instruction: Instruction) -> Option<Runner> {
+        if let Some(splitter) = &self.splitter {
+            splitter.find_runner(instruction)
+        } else {
+            self.handler.map(|h| h.runner)
+        }
+    }
+}
+
+enum Splitter {
+    Funct3Splitter(Box<[Option<OpcodeHandler>; 8]>),
+    GeneralSplitter(Box<[GeneralSplitterEntry]>),
+}
+
+impl Splitter {
+    fn find_runner(&self, instruction: Instruction) -> Option<Runner> {
+        match self {
+            Splitter::Funct3Splitter(f3s) => f3s[instruction.funct3() as usize]
+                .as_ref()
+                .and_then(|h| h.find_runner(instruction)),
+            Splitter::GeneralSplitter(entries) => {
+                for entry in entries {
+                    if instruction.0 & entry.mask == entry.value {
+                        return Some(entry.handler.runner);
+                    }
+                }
+
+                None
+            }
+        }
+    }
+}
+
+struct GeneralSplitterEntry {
+    mask: Word,
+    value: Word,
+    handler: InstructionHandler,
+}

src/lib.rs

@@ -1,4 +1,5 @@
 mod consts;
 pub mod core;
 mod decode;
+mod instructions;
 pub mod mem;