Huge performance boost.

src/bbp.rs

@@ -1,7 +1,7 @@
 pub fn get_byte(id: i32) -> u8 {
     let pid : f64 = 4.0 * series(1, id) - 2.0 * series(4, id) - series(5, id) - series(6, id);
 
-    let y : f64 = (pid - (pid as i32) as f64 + 1.0).abs(); // TODO use .trunc() instead
+    let y : f64 = (pid - (pid as i32) as f64 + 1.0).abs();
     let y = 16.0 * (y - y.floor());
 
     ((y as u8) << 4) | (16.0 * (y - y.floor())) as u8
@@ -86,13 +86,17 @@ fn expm(p: f64, ak: f64) -> f64 {
 }
 
 #[cfg(test)]
-mod tests { // TODO: use a tests directory instead?
-    use super::get_byte;
+mod tests {
+    use super::*;
 
     #[test]
     fn test_get_byte() {
         assert_eq!(36, get_byte(0));
+        assert_eq!(67, get_byte(1));
+        assert_eq!(63, get_byte(2));
+
         assert_eq!(163, get_byte(10));
+
         assert_eq!(41, get_byte(100));
     }
 }

src/main.rs

@@ -1,10 +1,8 @@
+#[macro_use] extern crate lazy_static;
 extern crate getopts;
 extern crate byteorder;
 extern crate pbr;
 
-#[macro_use]
-extern crate lazy_static;
-
 
 use std::env;
 use std::fs;
@@ -12,6 +10,7 @@ use std::io::BufReader;
 use std::io::prelude::*;
 use std::i32;
 use std::io::Cursor;
+use std::collections::BTreeMap;
 
 use getopts::Options;
 use byteorder::{ReadBytesExt, WriteBytesExt, LittleEndian};
@@ -21,6 +20,37 @@ use pbr::{ProgressBar, Units};
 mod bbp;
 
 
+struct Pi {
+    next: i32,
+    map: BTreeMap<u8, i32>
+}
+
+impl Pi {
+    fn new() -> Self {
+        Pi {
+            next: 0,
+            map: BTreeMap::new()
+        }
+    }
+
+    fn find(&mut self, byte: u8) -> i32 {
+        if self.map.contains_key(&byte) {
+            *self.map.get(&byte).unwrap()
+        } else {
+            for i in self.next..i32::MAX {
+                if byte == bbp::get_byte(i) {
+                    self.map.insert(byte, i);
+
+                    return i;
+                }
+            }
+
+            0
+        }
+    }
+}
+
+
 fn print_usage(program: &str, opts: Options) {
     let brief = format!("Usage: {} [option] INPUT OUTPUT", program);
     print!("{}", opts.usage(&brief));
@@ -82,20 +112,16 @@ fn compress(input: &str, output: &str) {
 
     let input_buf = BufReader::new(input_file);
 
-    let mut i : i32 = 0;
     let mut pb = ProgressBar::new(n_bytes);
 
+    let mut pi = Pi::new();
+
     pb.set_units(Units::Bytes);
 
     for b in input_buf.bytes() {
         let b = b.unwrap();
 
-        for n in 0..i32::MAX {
-            if b == bbp::get_byte(n) {
-                i = n;
-                break;
-            }
-        }
+        let i = pi.find(b);
 
         let mut index : Vec<u8> = vec![];