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Mersenne Prime — M61 for Hashing
It is easy to calculate modulus using this prime (with bitwise operations, it is well known)!
My question is how can we efficiently calculate 
, where a and b can both have at most 61 bits.
UPD: Found a function here that multiplies 64 bit with 32 bit while maintaining modulo. Can it be extended for 64 bit multiplied with 64 bit efficiently?
