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(svn r11454) -Fix: the CHANCE16 functions were biased; a 32768 in 65536 chance was really a 32769 in 65536 chance.

This commit is contained in:
rubidium 2007-11-17 23:16:41 +00:00
parent 32202be452
commit 80a7a91730
2 changed files with 15 additions and 10 deletions
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15
src/macros.h
View File

@ -476,7 +476,7 @@ template<typename T> static inline bool IS_INSIDE_1D(const T x, const int base,
* @param b The denominator of the fraction, must of course not be null
* @return True in (a/b) percent
*/
#define CHANCE16(a, b) ((uint16)Random() <= (uint16)((65536 * (a)) / (b)))
#define CHANCE16(a, b) CHANCE16I(a, b, Random())
/**
* Flips a coin with a given probability and saves the randomize-number in a variable.
@ -484,18 +484,25 @@ template<typename T> static inline bool IS_INSIDE_1D(const T x, const int base,
* This macro uses the same parameters as the CHANCE16 marco. 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.
*
* @param a The numerator of the fraction, see CHANCE16
* @param b The denominator of the fraction, see CHANCE16
* @param r The variable to save the randomize-number from Random()
* @return True in (a/b) percent
*/
#define CHANCE16R(a, b, r) ((uint16)(r = Random()) <= (uint16)((65536 * (a)) / (b)))
#define CHANCE16R(a, b, r) CHANCE16I(a, b, r = Random())
/**
* Checks if a given randomize-number is below a given probability.
*
* This macro is used to check if the given probability by the fraction of (a/b)
* is greater than the given randomize-number v.
* 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, see CHANCE16
* @param b The denominator of the fraction, see CHANCE16
@ -504,7 +511,7 @@ template<typename T> static inline bool IS_INSIDE_1D(const T x, const int base,
*/
static inline bool CHANCE16I(const uint a, const uint b, const uint32 r)
{
return (uint16)r <= (uint16)((65536 * a) / b);
return (uint16)r < (uint16)((65536 * a) / b);
}

10
src/town_cmd.cpp
View File

@ -731,16 +731,14 @@ no_slope:
* maybe terraform some. */
desired_slope = (dir == DIAGDIR_NW || dir == DIAGDIR_SE) ? SLOPE_NW : SLOPE_NE;
if (desired_slope != cur_slope && ComplementSlope(desired_slope) != cur_slope) {
uint32 r = Random();
if (CHANCE16I(1, 8, r)) {
if (CHANCE16(1, 8)) {
CommandCost res = CMD_ERROR;
if (!_generating_world && CHANCE16I(1, 10, r >> 4)) {
if (!_generating_world && CHANCE16(1, 10)) {
/* Note: Do not replace " ^ 0xF" with ComplementSlope(). The slope might be steep. */
res = DoCommand(tile, CHANCE16I(1, 16, r >> 8) ? cur_slope : cur_slope ^ 0xF, 0,
res = DoCommand(tile, CHANCE16(1, 16) ? cur_slope : cur_slope ^ 0xF, 0,
DC_EXEC | DC_AUTO | DC_NO_WATER, CMD_TERRAFORM_LAND);
}
if (CmdFailed(res) && CHANCE16I(1, 3, r >> 16)) {
if (CmdFailed(res) && CHANCE16(1, 3)) {
/* We can consider building on the slope, though. */
goto no_slope;
}