simplify pushdown logic

Author: kirjavascript

tests/src/pushdown.rs

@@ -5,6 +5,7 @@ pub fn test() {
 
     for pushdown in 2..15 {
         [0..1000, 24500..25500, 60000..65536].into_iter().for_each(|range| {
+        // [0..65535].into_iter().for_each(|range| {
             for score in range {
                 score::set(&mut emu, score);
 
@@ -22,24 +23,22 @@ pub fn test() {
 }
 
 // reference implementation - tested against the original game
-// may seem weird - designed to be translated to assembly
 fn pushdown_impl(pushdown: u8, score: u16) -> u16 {
     let ones = score % 10;
     let hundredths = score % 100;
-    let mut newscore = ones as u8 + (pushdown - 1);
-    if newscore & 0xF > 9 {
-        newscore += 6;
-    }
-
-    let low = (newscore & 0xF) as u16;
-    let high = ((newscore & 0xF0) / 16 * 10) as u16;
 
-    let mut newscore = high + (hundredths - ones);
-    let nextscore = newscore + low;
+    let mut added = ones + (pushdown as u16 - 1);
 
-    if nextscore <= 100 {
-        newscore = nextscore;
+    if added & 0xF > 9 {
+        added += 6;
     }
 
-    newscore - hundredths
+    let low = added & 0xF;
+    let high = (added >> 4) * 10;
+
+    if high + low + hundredths - ones <= 100 {
+        high + low - ones
+    } else {
+        high - ones
+    }
 }