fix calculation for storm sinking the ship

2 files changed, 39 insertions, 12 deletions

diff --git a/README.txt b/README.txt
index f793dfa..c0e1c1e 100644
--- a/README.txt
+++ b/README.txt
@@ -36,8 +36,8 @@ What's missing:
 
 Build Requirements:
 
-- GNU make. I use version 3.82, but I don't use any of its special
-  features, so any version should do.
+- make. I use GNU make 3.82, and occasionally test with an old
+  version of BSD make (which works).
 
 - cc65. Originally I used version 2.13.3, and part way through I
   upgraded to a git snapshot dated December 29, 2015. cc65-2.3.13
@@ -117,9 +117,10 @@ monitor with S-Video (separate chroma/luma) inputs. If all else fails,
 try turning the color knob all the way down (and the contrast as high
 as you can stand it). In emulators, you can just disable artifacting.
 
-On PAL systems, the ship explosions and sinking animations will be a bit
-slower, and the prompt timeouts will be a bit longer. I don't think this
-is a real issue (it's not like Taipan is a fast-paced arcade game).
+On PAL systems, the ship explosions and sinking animations will be 20%
+slower, and the prompt timeouts will be 20% longer (1 sec => 1.2 sec). I
+don't think this is a real issue (it's not like Taipan is a fast-paced
+arcade game).
 
 Bugs! At least these:
 
@@ -164,6 +165,13 @@ Bugs! At least these:
   If you have e.g. 1,190,000, that should show as 1.2 million, not 1.1...
   or maybe not (need to double-check against the Apple version).
 
+- One of my playtesters reported that, when running away from combat, it
+  said 4 billion ships were attacking (number of ships must have gone
+  negative).
+
+- After a fight, "Arriving at Manila" or such appears on the fight screen
+  without clearing it first (if you ran away, you can still see ships).
+
 Differences between the Apple II original and Linux port:
 
 1. Linux has an 80-column screen layout, Apple is 40.
diff --git a/taipan.c b/taipan.c
index 27f2adb..8080d13 100644
--- a/taipan.c
+++ b/taipan.c
@@ -74,8 +74,15 @@ extern void clrtoeol();
 
 /**** End of atari-specific stuff */
 
+/* old version of this used to just 'return randl()%clamp'.
+	If clamp were 0, the return value would be the unclamped
+	result from randl() (x % 0 == x, in cc65). If it were 1,
+	the return value would always be 1 (no randomness there). */
 unsigned long randclamp(unsigned long clamp) {
-	return randl() % clamp;
+	unsigned long r = randl();
+	if(clamp == 0) return clamp;
+	if(clamp == 1) return r & 0x01;
+	return r % clamp;
 }
 
 /* wrapper for cgetc() that returns letters as lowercase only
@@ -893,7 +900,7 @@ int sea_battle(int id, int num_ships) {
 			// cc65 runtime can't detect it...
 			// If ((ed * i * id)/2)) works out to 1, anything%1 is 0.
 			// damage = damage + (randi() % ((ed * i * id)/2)) + (i / 2);
-			// The is to avoid to % operator if the 2nd arg would be
+			// The answer is to avoid to % operator if the 2nd arg would be
 			// 0 or 1: the intended result would just be 0 or 1 anyway.
 
 			newdamage = ((ed * i * id)/2) + (i / 2);
@@ -1608,7 +1615,8 @@ void transfer(void)
 void quit(void)
 {
    int choice = 0,
-       result = 0;
+       result = 0,
+		 damagepct, sunk;
 
 	compradores_report();
    cputs("Taipan, do you wish me to go to:\r\n");
@@ -1688,7 +1696,7 @@ void quit(void)
          num_ships = randi()%((capacity / 5) + guns) + 5;
 
 			cprintulong(num_ships);
-         cputs("ships of Li Yuen's pirate\r\n");
+         cputs(" ships of Li Yuen's pirate\r\n");
          cputs("fleet, Taipan!!\r\n");
 
          timed_getch(TMOUT_3S);
@@ -1739,10 +1747,21 @@ void quit(void)
          cputs("   I think we're going down!!\r\n\n");
          timed_getch(TMOUT_3S);
 
-			// FIXME: the randclamp() version of this is broken badly!
          // if (((damage / capacity * 3) * ((float) randi() / RAND_MAX)) >= 1)
-			if(randclamp(damage / capacity * 3) >= 1)
-         {
+			// in the float version, damage/capacity*3 is your damage percentage,
+			// scaled 0 (0%) to 3 (100%). So if you're less than 34% damaged,
+			// you have no chance of sinking. If you're 34%-66% damaged, you
+			// have a 1 in 3 chance. If you're over 66%, you have a 2 in
+			// 3 chance.
+			damagepct = damage * 100 / capacity;
+			if(damagepct < 34)
+				sunk = 0;
+			else if(damagepct < 67)
+				sunk = randclamp(3) == 0;
+			else
+				sunk = randclamp(3) != 0;
+
+         if(sunk) {
             cputs("We're going down, Taipan!!\r\n");
             timed_getch(TMOUT_5S);