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Cleanup of Lookup3 hash #626

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Cleanup of Lookup3 hash #626

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87513bc
add missing GC preserve to lookup3
nhz2 Dec 30, 2024
16607a5
add more test hashes
nhz2 Dec 30, 2024
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36 changes: 17 additions & 19 deletions src/Lookup3.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -3,8 +3,6 @@

# 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.

Expand Down Expand Up @@ -48,13 +46,13 @@
# 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)
a -= c; a ⊻= bitrotate(c, 4); c += b
b -= a; b ⊻= bitrotate(a, 6); a += c
c -= b; c ⊻= bitrotate(b, 8); b += a
a -= c; a ⊻= bitrotate(c,16); c += b
b -= a; b ⊻= bitrotate(a,19); a += c
c -= b; c ⊻= bitrotate(b, 4); b += a
(a, b, c)

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end

# # -------------------------------------------------------------------------------
Expand All @@ -81,14 +79,14 @@
# 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
c ⊻= b; c -= bitrotate(b,14)
a ⊻= c; a -= bitrotate(c,11)
b ⊻= a; b -= bitrotate(a,25)
c ⊻= b; c -= bitrotate(b,16)
a ⊻= c; a -= bitrotate(c, 4)
b ⊻= a; b -= bitrotate(a,14)
c ⊻= b; c -= bitrotate(b,24)
c

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end

# -------------------------------------------------------------------------------
Expand Down Expand Up @@ -117,12 +115,12 @@
# -------------------------------------------------------------------------------
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)
GC.@preserve k 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
a = b = c = 0xdeadbeef + n%UInt32 + initval

# --------------- all but the last block: affect some 32 bits of (a,b,c)
ptr = k
Expand Down
11 changes: 11 additions & 0 deletions test/lookup3.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -15,3 +15,14 @@ for i = 1:length(large_buf)
end
@test JLD2.Lookup3.hash(large_buf) == 0x1bd2ee7b
@test JLD2.Lookup3.hash(fill!(large_buf, 0)) == 0x930c7afc

lookup3_test_hashes = [
0x276a0407, 0xc4f3b847, 0x3253e887, 0xf0dbeea6, 0xa496ca89, 0xa2773e81,
0xa88b6e6c, 0x2ca474f0, 0xe38ce8aa, 0xdb610bd1, 0x17f84daf, 0xccda323b,
0x114345a2, 0xc01e7c57, 0x636342ab, 0x17bd0180, 0xbed86ff9, 0xae721167,
0x9bc026d8, 0xaf53f65a, 0xbad83ad7, 0xcf6e279e, 0x8806c437, 0x4eaa9b13,
0x2b885021, 0x769e8a62, 0x7e5372be, 0xa70fa8be, 0x8b7a3c59, 0x17770551,
]
for (i, h) in enumerate(lookup3_test_hashes)
@test JLD2.Lookup3.hash(b"Four score and seven years ago"[begin:i]) == h
end
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