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38 lines
1.5 KiB
C++
38 lines
1.5 KiB
C++
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//-----------------------------------------------------------------------------------------------
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// RawNoise.cpp
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//
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#include "./RawNoise.hpp"
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namespace SquirrelNoise4 {
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//-----------------------------------------------------------------------------------------------
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// Fast hash of an int32 into a different (unrecognizable) uint32.
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//
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// Returns an uint32_t containing 32 reasonably-well-scrambled bits, based on the hash
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// of a given (signed) integer input parameter (position/index) and [optional] seed. Kind of
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// like looking up a value in an infinitely large table of previously generated random numbers.
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//
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// The bit-noise constants and bit-shifts were evolved by a genetic algorithm using the
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// "BigCrush" test for fitness, and have so far produced excellent test results.
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//
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// I call this particular approach SquirrelNoise (version 4).
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//
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uint32_t Get1dNoiseUint32( int32_t positionX, uint32_t seed ) {
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const uint32_t BIT_NOISE1 = 0xD2A80A23; // 0b1101'0010'1010'1000'0000'1010'0010'0011;
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const uint32_t BIT_NOISE2 = 0xA884F197; // 0b1010'1000'1000'0100'1111'0001'1001'0111;
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const uint32_t BIT_NOISE3 = 0x1B56C4E9; // 0b0001'1011'0101'0110'1100'0100'1110'1001;
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uint32_t mangledBits = (uint32_t) positionX;
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mangledBits *= BIT_NOISE1;
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mangledBits += seed;
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mangledBits ^= (mangledBits >> 7);
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mangledBits += BIT_NOISE2;
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mangledBits ^= (mangledBits >> 8);
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mangledBits *= BIT_NOISE3;
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mangledBits ^= (mangledBits >> 11);
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return mangledBits;
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}
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} // SquirrelNoise4
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