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

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frosch 2009-04-09 22:37:59 +00:00
parent 28bce241fd
commit d3de4ba91b
1 changed files with 3 additions and 3 deletions
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6
src/core/random_func.hpp
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@ -108,7 +108,7 @@ static FORCEINLINE uint32 InteractiveRandomRange(uint16 max)
* Checks if a given randomize-number is below a given probability. * 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) * 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 * 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, * the same result. One can use a random number for two calls to Chance16I,
@ -117,12 +117,12 @@ static FORCEINLINE uint32 InteractiveRandomRange(uint16 max)
* @param a The numerator of the fraction * @param a The numerator of the fraction
* @param b The denominator of the fraction, must of course not be null * @param b The denominator of the fraction, must of course not be null
* @param r The given randomize-number * @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) static FORCEINLINE bool Chance16I(const uint a, const uint b, const uint32 r)
{ {
assert(b != 0); assert(b != 0);
return (uint16)r < (uint16)(((a << 16) + b / 2) / b); return (((uint16)r * b + b / 2) >> 16) < a;
} }
/** /**