Spatial Hashing
Hash integer coordinates <x,y,z>. A good hash should make small input changes produce very different outputs.
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std::size_t operator()(const TileKey &k) const {
// Combine with a simple hash
std::size_t h = std::hash<int>()(k.x);
h ^= std::hash<int>()(k.y) + 0x9e3779b9 + (h << 6) + (h >> 2);
h ^= std::hash<int>()(k.z) + 0x9e3779b9 + (h << 6) + (h >> 2);
return h;
}
This is essentially the classic Boost hash_combine style formula. It is widely used for combining hashes of multiple fields.:
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seed ^= value + 0x9e3779b9 + (seed << 6) + (seed >> 2);
^=XORs the new mixed value into the current hash.h ^= hash(y) + C + (h << 6) + (h >> 2);is basicallyh ^= (std::hash<int>()(k.y) + C + (h << 6) + (h >> 2));
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0x9e3779b9: A magic constant often used in hash combining. It comes from the fractional part of the golden ratio and helps spread bits around. (h << 6) and (h >> 2)These shift the current hash left and right before mixing, so the order matters and nearby values do not combine too simply.
