wip: extract the xexdb tool closure

crates/sylpheed-ppc/examples/decode_table_check.rs

@@ -0,0 +1,37 @@
+//! Cross-check our decoder against xenia-canary's authoritative encoding table.
+//!
+//! Canary's `ppc_opcode_table_gen.cc` lists, for every opcode it knows, a
+//! representative instruction word with the operand fields zeroed. Feeding each
+//! word to our decoder must yield the matching opcode — anything else is a hole
+//! or a mis-decode in our tables.
+//!
+//! ```text
+//! cargo run --release -p xenia-cpu --example decode_table_check -- <table.txt>
+//! ```
+//! where each line is `0xWORD name`.
+use std::io::BufRead;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let path = std::env::args().nth(1).ok_or("usage: decode_table_check <table>")?;
+    let f = std::io::BufReader::new(std::fs::File::open(path)?);
+    let (mut ok, mut bad, mut invalid) = (0u32, 0u32, 0u32);
+    for line in f.lines() {
+        let line = line?;
+        let mut it = line.split_whitespace();
+        let (Some(w), Some(name)) = (it.next(), it.next()) else { continue };
+        let word = u32::from_str_radix(w.trim_start_matches("0x"), 16)?;
+        let d = sylpheed_ppc::decoder::decode(word, 0x8200_0000);
+        let got = format!("{:?}", d.opcode);
+        if got == name {
+            ok += 1;
+        } else if got == "Invalid" {
+            invalid += 1;
+            println!("MISSING  {w} {name:<14} -> Invalid");
+        } else {
+            bad += 1;
+            println!("MISMATCH {w} {name:<14} -> {got}");
+        }
+    }
+    println!("\nmatched {ok}, mismatched {bad}, missing {invalid}");
+    Ok(())
+}