cpp/openttd-patchpack/source Changeset - r11621:2521e2714f58

Changeset - r11621:2521e2714f58

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frosch - 15 years ago 2009-04-09 22:37:59
frosch@openttd.org

(svn r16006) -Fix (r0): Chance16() did not work for b = 1. Also transform the formula to not use divisions.

1 file changed with 3 insertions and 3 deletions:

src/core/random_func.hpp

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src/core/random_func.hpp

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@@ @@ -108,7 +108,7 @@ static FORCEINLINE uint32 InteractiveRan @@
  * Checks if a given randomize-number is below a given probability.
+ *
  * This function is used to check if the given probability by the fraction of (a/b)
- * is greater than low 16 bits of the given randomize-number v.
+ * is greater than low 16 bits of the given randomize-number r.
+ *
  * Do not use this function twice on the same random 16 bits as it will yield
  * the same result. One can use a random number for two calls to Chance16I,
@@ @@ -117,12 +117,12 @@ static FORCEINLINE uint32 InteractiveRan @@
  * @param a The numerator of the fraction
  * @param b The denominator of the fraction, must of course not be null
  * @param r The given randomize-number
- * @return True if v is less or equals (a/b)
+ * @return True if the probability given by r is less or equal to (a/b)
  */
 static FORCEINLINE bool Chance16I(const uint a, const uint b, const uint32 r)
+{
 	assert(b != 0);
-	return (uint16)r < (uint16)(((a << 16) + b / 2) / b);
+	return (((uint16)r * b + b / 2) >> 16) < a;
+}
 /**

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