inverse_hash.jl

using Compat

# Original C version at https://naml.us/post/inverse-of-a-hash-function/
function inverse_hash(key::UInt64)
    local tmp::UInt64

    # Invert key = key + (key << 31)
    tmp = key-(key<<31)
    key = key-(tmp<<31)

    # Invert key = key ^ (key >> 28)
    tmp = xor(key, key>>28)
    key = xor(key, tmp>>28)

    # Invert key *= 21
    key *= 0xcf3cf3cf3cf3cf3d

    # Invert key = key ^ (key >> 14)
    tmp = xor(key, key>>14)
    tmp = xor(key, tmp>>14)
    tmp = xor(key, tmp>>14)
    key = xor(key, tmp>>14)

    # Invert key *= 265
    key *= 0xd38ff08b1c03dd39

    # Invert key = key ^ (key >> 24)
    tmp = xor(key, key>>24)
    key = xor(key, tmp>>24)

    # Invert key = (~key) + (key << 21)
    tmp = ~key
    tmp = ~(key-(tmp<<21))
    tmp = ~(key-(tmp<<21))
    key = ~(key-(tmp<<21))

    key
end