Update src/riscv_insns.rs with new instruction handling logic

Author: tommythorn

src/riscv_insns.rs

@@ -0,0 +1,54 @@
+use std::collections::HashMap;
+
+type Instruction = (u32, u32, &'static str);
+
+pub const INSTRUCTIONS: [(u32, u32, &str); 204] = [
+    (0xe003, 0x0000, "c.addi4spn"),
+    (0xe003, 0x2000, "c.fld"),
+    (0xe003, 0x4000, "c.lw"),
+    (0xfe00707f, 0x0e007033, "czero.nez"), // Example instructions
+];
+
+/// Build a fast 2048-elements dispatch table for accelerated lookup
+pub fn build_dispatch_table() -> [&'static [(u32, u32, &'static str)]; 2048] {
+    const EMPTY: &[Instruction] = &[];
+
+    let mut dispatch_table: [&[(u32, u32, &str)]; 2048] = [EMPTY; 2048];
+    let mut temp_table: Vec<Vec<Instruction>> = vec![vec![]; 2048];
+
+    for &(mask, pattern, mnemonic) in INSTRUCTIONS.iter() {
+        let index = ((pattern & 127) + ((pattern & 0xe000) >> 5)) as usize;
+        temp_table[index].push((mask, pattern, mnemonic));
+    }
+
+    for (i, instructions) in temp_table.into_iter().enumerate() {
+        if !instructions.is_empty() {
+            dispatch_table[i] = Box::leak(instructions.into_boxed_slice());
+        }
+    }
+
+    dispatch_table
+}
+
+pub fn match_instruction(w: u32, dispatch_table: &[&[(u32, u32, &'static str)]; 2048]) -> Option<&'static str> {
+    let index = ((w & 127) + ((w & 0xe000) >> 5)) as usize;
+
+    for &(mask, pattern, mnemonic) in dispatch_table[index].iter() {
+        if (w & mask) == pattern {
+            return Some(mnemonic);
+        }
+    }
+
+    None
+}
+
+#[test]
+fn test_dispatch_array() {
+    let dispatch_table = build_dispatch_table();
+    let w: u32 = 0x00000033;
+    if let Some(mnemonic) = match_instruction(w, &dispatch_table) {
+        println!("Instruction matched: {}", mnemonic);
+    } else {
+        println!("No matching instruction found!");
+    }
+}