From bdc7fd2d765b84dc17415ecda0bef31471befa91 Mon Sep 17 00:00:00 2001
From: skidd13 <skidd13@openttd.org>
Date: Sun, 25 Nov 2007 15:35:25 +0000
Subject: (svn r11523) -Codechange: Move the CHANCE macros to
 core/random_func.cpp cause they depend on Random() -Codechange: Convert the
 CHANCE macros to functions and rename them fitting to the naming style

---
 src/core/random_func.hpp | 59 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

(limited to 'src/core/random_func.hpp')

diff --git a/src/core/random_func.hpp b/src/core/random_func.hpp
index 3806bc01a..a2e0ea984 100644
--- a/src/core/random_func.hpp
+++ b/src/core/random_func.hpp
@@ -36,4 +36,63 @@ void SetRandomSeed(uint32 seed);
 uint32 InteractiveRandom(); // Used for random sequences that are not the same on the other end of the multiplayer link
 uint InteractiveRandomRange(uint max);
 
+/**
+ * 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.
+ *
+ * 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,
+ * where one call sends the low 16 bits and the other the high 16 bits.
+ *
+ * @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)
+ */
+static inline bool Chance16I(const uint a, const uint b, const uint32 r)
+{
+	assert(b != 0);
+	return (uint16)r < (uint16)((a << 16) / b);
+}
+
+/**
+ * Flips a coin with a given probability.
+ *
+ * This macro can be used to get true or false randomized according to a
+ * given probability. The parameter a and b create a percent value with
+ * (a/b). The macro returns true in (a/b) percent.
+ *
+ * @see Chance16I()
+ * @param a The numerator of the fraction
+ * @param b The denominator of the fraction
+ * @return True in (a/b) percent
+ */
+static inline bool Chance16(const uint a, const uint b)
+{
+	return Chance16I(a, b, Random());
+}
+
+/**
+ * Flips a coin with a given probability and saves the randomize-number in a variable.
+ *
+ * This function uses the same parameters as Chance16. The third parameter
+ * must be a variable the randomize-number from Random() is saved in.
+ *
+ * The low 16 bits of r will already be used and can therefor not be passed to
+ * Chance16I. One can only send the high 16 bits to Chance16I.
+ *
+ * @see Chance16I()
+ * @param a The numerator of the fraction
+ * @param b The denominator of the fraction
+ * @param r The variable to save the randomize-number from Random()
+ * @return True in (a/b) percent
+ */
+static inline bool Chance16R(const uint a, const uint b, uint32 &r)
+{
+	r = Random();
+	return Chance16I(a, b, r);
+}
+
 #endif /* RANDOM_FUNC_HPP */
-- 
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