From 9175c4c23409e798d4c03ab4e561767d2cf69e33 Mon Sep 17 00:00:00 2001
From: Lawrence Kesteloot <lk@teamten.com>
Date: Thu, 2 Aug 2018 14:52:23 -0700
Subject: [PATCH] Reduce unnecessary push/pop in expression compilation.

---
 main.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/main.c b/main.c
index b6d0a56..6a44822 100644
--- a/main.c
+++ b/main.c
@@ -371,18 +371,24 @@ static uint16_t parse_uint16(uint8_t **s_ptr) {
  */
 static uint8_t *compile_expression(uint8_t *s) {
     int plus_count = 0;
+    char have_value_in_ax = 0;
 
     while (1) {
         if (*s >= '0' && *s <= '9') {
             // Parse number.
-            uint16_t value = parse_uint16(&s);
+            uint16_t value;
+
+            if (have_value_in_ax) {
+                // Push on the number stack.
+                add_call(pushax);
+            }
+
+            value = parse_uint16(&s);
             g_compiled[g_compiled_length++] = I_LDX;
             g_compiled[g_compiled_length++] = value >> 8;
             g_compiled[g_compiled_length++] = I_LDA;
             g_compiled[g_compiled_length++] = value & 0xFF;
-
-            // Push on the number stack.
-            add_call(pushax);
+            have_value_in_ax = 1;
         } else if (*s == '+') {
             plus_count += 1;
             s += 1;
@@ -391,9 +397,6 @@ static uint8_t *compile_expression(uint8_t *s) {
         }
     }
 
-    // Pop the last value from the number stack.
-    add_call(popax);
-
     while (plus_count > 0) {
         add_call(tosaddax);
         plus_count -= 1;