A simple, self-contained way to generate location-specific, on-demand pseudorandon number for procedural content generation by hash coordinates

SpatialRandom-snippet.cpp

/*
 * A code snippet (not the whole thing) or a system for 
 * generating sequences of random number at points in 
 * space and "time" (sequence order) by hashing 4-dimensional
 * coordinates.  The purpose of this is for use in 
 * procedural content generation, as an alternative to 
 * complex systems of region / chunk / area seed calculations.
 * This allows for any of the needed pseudorandom numbers 
 * to be generated on demand, in any order, as many times 
 * as required -- easily adapting to worlds generating in 
 * unpredictable order based on player actions and location.
 * 
 * As a side benefit and instance (class static or global) 
 * with a hardcoded magic number for a seed can be used 
 * to has location specific data for storage in a hashmap 
 * style cache.
 * 
 * For fewer dimension, of course, it can be simplified.
 * 
 * Other data types are easily dirived, of course.  For 
 * example, taking only lower order bits for smaller 
 * integral types or dividing by 0xffffffffffffffff to 
 * get floating point types.
 * 
 * Fuller implementations can be found at: 
 * https://github.com/BlackJar72/MyLibraries/blob/master/GameMath/src/SpatialRandom.cpp
 * 
 * ...and for a Java version at:
 * https://github.com/BlackJar72/ProcGenLab/blob/master/src/jaredbgreat/procgenlab/api/util/SpatialNoise.java
 * 
 */

inline long rrotate(const long &in, const int &by) const {
    return ((in >> by) | (in << (64 - by)));
}

inline long lrotate(const long &in, const int &by) const {
    return ((in << by) | (in >> (64 - by)));
}


unsigned long long SpatialNoise::longFor(const int &x, const int &y, const int &z, const int &t) const {
    long long out = seed1 + (15485077L  * (long long)t)
                          + (12338621L  * (long long)x)
                          + (15485863L  * (long long)y)
                          + (14416417L  * (long long)z);
    long long alt = seed2 + (179424743L * (long long)t)
                          + (154858637L * (long long)y)
                          + (179426003L * (long long)x)
                          + (179425819L * (long long)z);
    alt ^= lrotate(alt, (x % 29) + 13);
    alt ^= rrotate(alt, (y % 31) + 7);
    alt ^= lrotate(alt, (z % 23) + 19);
    alt ^= rrotate(alt, (t % 43) + 11);
    out ^= lrotate(out, ((x & 0x7fffffff) % 13) + 5);
    out ^= rrotate(out, ((y & 0x7fffffff) % 11) + 28);
    out ^= lrotate(out, ((z & 0x7fffffff) % 7) + 13);
    out ^= rrotate(out, ((t & 0x7ffffff)% 17) + 45);
    return (out ^ alt);
}