Save 11 bytes

3 files changed, 19 insertions, 3 deletions

diff --git a/NOTES.txt b/NOTES.txt
index 6d8d37f..6825336 100644
--- a/NOTES.txt
+++ b/NOTES.txt
@@ -23,6 +23,10 @@ arcade game).
 
 Deliberate differences between the Apple II and Atari ports:
 
+0. The Atari version is noticeably faster than the Apple version on II+ or
+   IIe. This is because it's written in C and assembly, not interpreted
+   BASIC. A IIgs on the other hand...
+
 1. "Press ESC for help" rather than ESC to start. Starting the game is
    done with the space bar or return key.
 
diff --git a/rand.s b/rand.s
index a284592..6efcabd 100644
--- a/rand.s
+++ b/rand.s
@@ -1,5 +1,5 @@
 
- .export _randl
+ .export _randl, _rand1to3
  .import _rand
 ; .export _randb, _randi, _randl
 ; .export _rand1in5
@@ -27,6 +27,16 @@ _randl:
  ldx tmp3
  rts
 
+; return 1, 2, or 3. equivalent to: randi()%3+1
+; replacing both occurences of the expression in taipan.c with a calls
+; to this function saves 11 bytes.
+_rand1to3:
+	jsr _rand      ; returns 16 bits: X is MSB (which we ignore), A is LSB
+	and #$03       ; A now 0..3
+	beq _rand1to3  ; try again, if it's 0
+	ldx #0         ; now A is 1..3, but we have to force X to 0...
+	rts
+
  ;;; rest of file is commented out
 
 ; RANDOM is the POKEY LFSR read address. According to the POKEY data
diff --git a/taipan.c b/taipan.c
index bd67589..d1cb8ed 100644
--- a/taipan.c
+++ b/taipan.c
@@ -97,6 +97,8 @@ extern unsigned int __fastcall__ randi(void);
 #define randi() ((unsigned int)rand())
 #endif
 
+extern unsigned char rand1to3(void);
+
 /* random long, 0 to 2**32-1 */
 extern unsigned long __fastcall__ randl(void);
 
@@ -1626,7 +1628,7 @@ void cash_or_guns(void) {
 void set_prices(void) {
 	char i;
 	for(i = 0; i < 4; ++i)
-		price[i] = base_price[i][port] / 2 * (randi()%3 + 1) * base_price[i][0];
+		price[i] = base_price[i][port] / 2 * rand1to3() * base_price[i][0];
 }
 
 unsigned int warehouse_in_use() {
@@ -2825,7 +2827,7 @@ void elder_brother_wu(void) {
    }
 
    if((debt > 20000) && (cash > 0) && (one_chance_in(5))) {
-      unsigned char num = randi()%3 + 1;
+      unsigned char num = rand1to3();
 
       cash = 0;
       port_stats();