An optimized JavaScript implementation of the MurmurHash-3 algorithm.
This algorithm takes a JavaScript string and a seed, and quickly creates a non-cryptographic 32-bit hash from it.
More information about this algorithm can be found at:
There is alternative earlier implementation available at:
My implementation is based on the observation that JavaScript is not limited to exactly 32-bit integers. Rather, it internally represents integers as double-precision floats. Therefore it is limited to 52-bit integers (the mantissa length). 52 bits is enough to contain 48 bits of information, and thanks to the flexibility of floating point it is able to do that for various exponents / shift positions. Therefore it is able to contain the result of multiplying 32-bit and 16-bit numbers without loss of lowest 16 bits for the low part of result, and without loss of next 16 bits for the high part of result - the latter is thanks to the flexibility of floating point - the lowest 16 bits are unused in the high part of result (the exponent part of floating point is correspondingly bigger) and next 48 bits are stored in the floating point mantissa, until highest 32 bits are cleared out in the code. This observation enables the algorithm to be implemented so that it requires less operations to emulate multiplications of 32-bit members, as compared to an algorithm that uses multiplications of 16-bit members to emulate multiplications of 32-bit members. Also because of that, addition of 32-bit operands can be performed simpler.
The performance comparison of the two algorithms can be found below. The performance varies across computers, in some computers they perform about same. In some computers my version is about 20% faster.
Result equality test against Gary's implementation is here:
Copyright (c) 2015 Roland Pihlakas
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