[PATCH] D41993: [ELF] - Change shift2 constant of GNU_HASH from 6->11.

[George Rimar via llvm-commits]

>>The bloom filter for the .gnu.hash table is a two-bit bloom filter. To choose two bit locations, we compute one hash value H and create

>>two hash values H1 and H2 in the following manner :Assume a 64-bit machine. Bits H[0,5] are always used for computing the
>>first hash H1. Bits H[Shift2, Shift2 + 5] are used for computing the second hash H2.?
>>As long as the hash function produces evenly distributed hash values, choosing bits [6, 11] isn't different from choosing other bits, say [15, 20].
>>No Shift2 greater than 5 should be better than any other Shift2 values in theory.
>>
>>Am I missing something?
>
>I think there is a mistake here. See, we have following code:
>Val |= uint64_t(1) << (Sym.Hash % C);
>Val |= uint64_t(1) << ((Sym.Hash >> getShift2()) % C);
>C == 64 for 64 bits, ot 2^6. It is simplified to:
>Val |= uint64_t(1) << (Sym.Hash >> 6);
>Val |= uint64_t(1) << (Sym.Hash >> (Shift2 + 6));
>Or I believe bits H[6, 63] are used to find Bit 1 and H[6 + Shift2, 63] for Bit 2.?
>
>George.

Sorry for noise, my simplification in incorrect, I read "%" as "/" by mistake.
You right about bits used.

George.
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