mirror of https://github.com/zeldaret/mm.git
97 lines
2.8 KiB
C
97 lines
2.8 KiB
C
#include "global.h"
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//! The latest generated random number, used to generate the next number in the sequence.
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static u32 sRandInt = 1;
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//! Space to store a value to be re-interpreted as a float.
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//! This can't be static because it is used in z_kankyo.
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u32 sRandFloat;
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//! These values are recommended by the algorithms book *Numerical Recipes in C. The Art of Scientific Computing*, 2nd
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//! Edition, 1992, ISBN 0-521-43108-5. (p. 284):
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//! > This is about as good as any 32-bit linear congruential generator, entirely adequate for many uses.
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#define RAND_MULTIPLIER 1664525
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#define RAND_INCREMENT 1013904223
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/**
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* Generates the next pseudo-random integer.
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*/
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u32 Rand_Next(void) {
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return sRandInt = (sRandInt * RAND_MULTIPLIER) + RAND_INCREMENT;
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}
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/**
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* Seeds the internal pseudo-random number generator with a provided starting value.
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*/
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void Rand_Seed(u32 seed) {
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sRandInt = seed;
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}
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/**
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* Returns a pseudo-random float between 0.0f and 1.0f from the internal PRNG.
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*
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* @note Works by generating the next integer, masking it to an IEEE-754 compliant float between 1.0f and 2.0f, and
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* subtracting 1.0f.
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*
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* @remark This is also recommended by Numerical Recipes, pp. 284-5.
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*/
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f32 Rand_ZeroOne(void) {
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sRandInt = (sRandInt * RAND_MULTIPLIER) + RAND_INCREMENT;
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sRandFloat = ((sRandInt >> 9) | 0x3F800000);
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return *((f32*)&sRandFloat) - 1.0f;
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}
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/**
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* Returns a pseudo-random float between -0.5f and 0.5f in the same way as Rand_ZeroOne().
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*/
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f32 Rand_Centered(void) {
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sRandInt = (sRandInt * RAND_MULTIPLIER) + RAND_INCREMENT;
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sRandFloat = ((sRandInt >> 9) | 0x3F800000);
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return *((f32*)&sRandFloat) - 1.5f;
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}
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//! All functions below are unused variants of the above four, that use a provided random number variable instead of the
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//! internal `sRandInt`
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/**
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* Seeds a provided pseudo-random number with a provided starting value.
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*
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* @see Rand_Seed
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*/
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void Rand_Seed_Variable(u32* rndNum, u32 seed) {
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*rndNum = seed;
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}
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/**
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* Generates the next pseudo-random number from the provided rndNum.
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*
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* @see Rand_Next
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*/
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u32 Rand_Next_Variable(u32* rndNum) {
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return *rndNum = (*rndNum * RAND_MULTIPLIER) + RAND_INCREMENT;
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}
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/**
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* Generates the next pseudo-random float between 0.0f and 1.0f from the provided rndNum.
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*
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* @see Rand_ZeroOne
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*/
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f32 Rand_ZeroOne_Variable(u32* rndNum) {
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u32 next = (*rndNum * RAND_MULTIPLIER) + RAND_INCREMENT;
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sRandFloat = ((*rndNum = next) >> 9) | 0x3F800000;
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return *((f32*)&sRandFloat) - 1.0f;
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}
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/**
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* Generates the next pseudo-random float between -0.5f and 0.5f from the provided rndNum.
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*
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* @see Rand_ZeroOne, Rand_Centered
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*/
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f32 Rand_Centered_Variable(u32* rndNum) {
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u32 next = (*rndNum * RAND_MULTIPLIER) + RAND_INCREMENT;
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sRandFloat = ((*rndNum = next) >> 9) | 0x3F800000;
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return *((f32*)&sRandFloat) - 1.5f;
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}
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