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Lookup3.jl
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Lookup3.jl
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module Lookup3
import JLD2: jlunsafe_load, pconvert
# Original source at http://www.burtleburtle.net/bob/c/lookup3.c
rot(x::UInt32, k) = xor(((x)<<(k)), ((x)>>(32-(k))))
# -------------------------------------------------------------------------------
# mix -- mix 3 32-bit values reversibly.
# This is reversible, so any information in (a,b,c) before mix() is
# still in (a,b,c) after mix().
# If four pairs of (a,b,c) inputs are run through mix(), or through
# mix() in reverse, there are at least 32 bits of the output that
# are sometimes the same for one pair and different for another pair.
# This was tested for:
# * pairs that differed by one bit, by two bits, in any combination
# of top bits of (a,b,c), or in any combination of bottom bits of
# (a,b,c).
# * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
# the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
# is commonly produced by subtraction) look like a single 1-bit
# difference.
# * the base values were pseudorandom, all zero but one bit set, or
# all zero plus a counter that starts at zero.
# Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
# satisfy this are
# 4 6 8 16 19 4
# 9 15 3 18 27 15
# 14 9 3 7 17 3
# Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing
# for "differ" defined as + with a one-bit base and a two-bit delta. I
# used http://burtleburtle.net/bob/hash/avalanche.html to choose
# the operations, constants, and arrangements of the variables.
# This does not achieve avalanche. There are input bits of (a,b,c)
# that fail to affect some output bits of (a,b,c), especially of a. The
# most thoroughly mixed value is c, but it doesn't really even achieve
# avalanche in c.
# This allows some parallelism. Read-after-writes are good at doubling
# the number of bits affected, so the goal of mixing pulls in the opposite
# direction as the goal of parallelism. I did what I could. Rotates
# seem to cost as much as shifts on every machine I could lay my hands
# on, and rotates are much kinder to the top and bottom bits, so I used
# rotates.
# -------------------------------------------------------------------------------
@inline function mix(a, b, c)
a -= c; a = xor(a, rot(c, 4)); c += b
b -= a; b = xor(b, rot(a, 6)); a += c
c -= b; c = xor(c, rot(b, 8)); b += a
a -= c; a = xor(a, rot(c,16)); c += b
b -= a; b = xor(b, rot(a,19)); a += c
c -= b; c = xor(c, rot(b, 4)); b += a
(a, b, c)
end
# # -------------------------------------------------------------------------------
# final -- final mixing of 3 32-bit values (a,b,c) into c
# Pairs of (a,b,c) values differing in only a few bits will usually
# produce values of c that look totally different. This was tested for
# * pairs that differed by one bit, by two bits, in any combination
# of top bits of (a,b,c), or in any combination of bottom bits of
# (a,b,c).
# * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
# the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
# is commonly produced by subtraction) look like a single 1-bit
# difference.
# * the base values were pseudorandom, all zero but one bit set, or
# all zero plus a counter that starts at zero.
# These constants passed:
# 14 11 25 16 4 14 24
# 12 14 25 16 4 14 24
# and these came close:
# 4 8 15 26 3 22 24
# 10 8 15 26 3 22 24
# 11 8 15 26 3 22 24
# -------------------------------------------------------------------------------
@inline function final(a, b, c)
c = xor(c, b); c -= rot(b,14)
a = xor(a, c); a -= rot(c,11)
b = xor(b, a); b -= rot(a,25)
c = xor(c, b); c -= rot(b,16)
a = xor(a, c); a -= rot(c,4)
b = xor(b, a); b -= rot(a,14)
c = xor(c, b); c -= rot(b,24)
c
end
# -------------------------------------------------------------------------------
# hashlittle() -- hash a variable-length key into a 32-bit value
# k : the key (the unaligned variable-length array of bytes)
# length : the length of the key, counting by bytes
# initval : can be any 4-byte value
# Returns a 32-bit value. Every bit of the key affects every bit of
# the return value. Two keys differing by one or two bits will have
# totally different hash values.
# The best hash table sizes are powers of 2. There is no need to do
# mod a prime (mod is sooo slow!). If you need less than 32 bits,
# use a bitmask. For example, if you need only 10 bits, do
# h = (h & hashmask(10));
# In which case, the hash table should have hashsize(10) elements.
# If you are hashing n strings (uint8_t **)k, do it like this:
# for (i=0, h=0; i<n; ++i) h = hashlittle( k[i], len[i], h);
# By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
# code any way you wish, private, educational, or commercial. It's free.
# Use for hash table lookup, or anything where one collision in 2^^32 is
# acceptable. Do NOT use for cryptographic purposes.
# -------------------------------------------------------------------------------
function hash(k::AbstractVector{UInt8}, istart::Integer=1, n::Integer=length(k), initval::UInt32=UInt32(0))
n <= length(k) || throw(BoundsError())
hash(pointer(k, istart), n, initval)
end
function hash(k::Ptr{UInt8}, n::Integer=length(k), initval::UInt32=UInt32(0))
# Set up the internal state
a = b = c = 0xdeadbeef + convert(UInt32, n) + initval
# --------------- all but the last block: affect some 32 bits of (a,b,c)
ptr = k
# @inbounds while n > 12
# a += k[offset]
# a += convert(UInt32, k[offset+1])<<8
# a += convert(UInt32, k[offset+2])<<16
# a += convert(UInt32, k[offset+3])<<24
# @show a
# b += k[offset+4]
# b += convert(UInt32, k[offset+5])<<8
# b += convert(UInt32, k[offset+6])<<16
# b += convert(UInt32, k[offset+7])<<24
# @show b
# c += k[offset+8]
# c += convert(UInt32, k[offset+9])<<8
# c += convert(UInt32, k[offset+10])<<16
# c += convert(UInt32, k[offset+11])<<24
# @show c
# (a, b, c) = mix(a, b, c)
# n -= 12
# offset += 12
# end
@inbounds while n > 12
a += jlunsafe_load(pconvert(Ptr{UInt32}, ptr))
ptr += 4
b += jlunsafe_load(pconvert(Ptr{UInt32}, ptr))
ptr += 4
c += jlunsafe_load(pconvert(Ptr{UInt32}, ptr))
(a, b, c) = mix(a, b, c)
ptr += 4
n -= 12
end
# -------------------------------- last block: affect all 32 bits of (c)
# @inbounds if n > 0
# n >= 12 && (c += convert(UInt32, k[offset+11])<<24)
# n >= 11 && (c += convert(UInt32, k[offset+10])<<16)
# n >= 10 && (c += convert(UInt32, k[offset+9])<<8)
# n >= 9 && (c += k[offset+8])
# n >= 8 && (b += convert(UInt32, k[offset+7])<<24)
# n >= 7 && (b += convert(UInt32, k[offset+6])<<16)
# n >= 6 && (b += convert(UInt32, k[offset+5])<<8)
# n >= 5 && (b += k[offset+4])
# n >= 4 && (a += convert(UInt32, k[offset+3])<<24)
# n >= 3 && (a += convert(UInt32, k[offset+2])<<16)
# n >= 2 && (a += convert(UInt32, k[offset+1])<<8)
# n >= 1 && (a += k[offset])
# c = final(a, b, c)
# end
@inbounds if n > 0
if n == 12
c += jlunsafe_load(pconvert(Ptr{UInt32}, ptr+8))
@goto n8
elseif n == 11
c += UInt32(jlunsafe_load(Ptr{UInt8}(ptr+10)))<<16
@goto n10
elseif n == 10
@label n10
c += UInt32(jlunsafe_load(Ptr{UInt8}(ptr+9)))<<8
@goto n9
elseif n == 9
@label n9
c += jlunsafe_load(ptr+8)
@goto n8
elseif n == 8
@label n8
b += jlunsafe_load(pconvert(Ptr{UInt32}, ptr+4))
@goto n4
elseif n == 7
@label n7
b += UInt32(jlunsafe_load(Ptr{UInt8}(ptr+6)))<<16
@goto n6
elseif n == 6
@label n6
b += UInt32(jlunsafe_load(Ptr{UInt8}(ptr+5)))<<8
@goto n5
elseif n == 5
@label n5
b += jlunsafe_load(ptr+4)
@goto n4
elseif n == 4
@label n4
a += jlunsafe_load(pconvert(Ptr{UInt32}, ptr))
elseif n == 3
@label n3
a += UInt32(jlunsafe_load(Ptr{UInt8}(ptr+2)))<<16
@goto n2
elseif n == 2
@label n2
a += UInt32(jlunsafe_load(Ptr{UInt8}(ptr+1)))<<8
@goto n1
elseif n == 1
@label n1
a += jlunsafe_load(ptr)
end
c = final(a, b, c)
end
c
end
end