c_random.cpp

Go to the documentation of this file.

#include <types.h>
#include <game/cLib/c_random.hpp>
/// @file
 
/// @ingroup clib
namespace cRandom {
    u32 l_RANDOM_MUL = 0x19660D; ///< Constant @p a from the @p ranqd1 algorithm.
    u32 l_RANDOM_ADD = 0x3C6EF35F; ///< Constant @p c from the @p ranqd1 algorithm.
}
 
// This decompiled terribly but at least it matches
// Original algorithm: https://s3.amazonaws.com/nrbook.com/book_C210_pdf/chap07c.pdf (page 284-285)
inline u32 cRandom_c::ranqdStep() {
 
    // Variables must be declared in this order or there will be regswaps
    register u32 c, b, a, x;
    x = mSeed;
    a = cRandom::l_RANDOM_MUL;
    b = cRandom::l_RANDOM_ADD;
 
    // Longlong math needs to be done in asm in order to match...
    asm {
        mulhwu c, x, a
        mullw x, x, a
        addc x, x, b
        adde x, x, c
    }
 
    return x;
}
 
u32 cRandom_c::getRandomByAsm(ulong max) {
    mSeed = ranqdStep();
    return ((u64) mSeed * max) >> 32;
}
 
float cRandom_c::getRandomFByAsm() {
    mSeed = ranqdStep();
    u32 tmp = 0x3f800000 | (mSeed >> 9 & 0x7fffff);
    return (*(float *)&tmp)-1.0f;
}
 
float cRandom_c::getRandomF2ByAsm() {
    mSeed = ranqdStep();
    u32 tmp = 0x3f800000 | (mSeed >> 9 & 0x7fffff);
    return (*(float *)&tmp)-1.5f;
}