xxhash
XxHash checksum

Vocabulary
checksums.xxhash

Class description
xxHash 32-bit checksum algorithm.

Definition

IN: checksums.xxhash

TUPLE: xxhash seed ;

Methods

USING: accessors alien.c-types checksums checksums.xxhash
checksums.xxhash.private combinators generalizations grouping
kernel math math.bitwise sequences ;

M:: xxhash checksum-bytes ( bytes checksum -- value )
    checksum seed>> :> seed bytes length :> len len dup 16 mod -
    :> len/16 len dup 4 mod - :> len/4 len 16 >= [
        seed prime1 w+ prime2 w+ seed prime2 w+
        seed seed prime1 w- 0 len/16 bytes uint native-mapper
        4 <groups> [
            first4
            [ prime2 w* w+ 13 bitroll-32 prime1 w* ] 4 napply
        ] each {
            [ 1 bitroll-32 ]
            [ 7 bitroll-32 ]
            [ 12 bitroll-32 ]
            [ 18 bitroll-32 ]
        } spread w+ w+ w+
    ] [ seed prime5 w+ ] if len w+
    len/16 len/4 bytes uint native-mapper
    [ prime3 w* w+ 17 bitroll-32 prime4 w* ] each
    bytes len/4 tail-slice
    [ prime5 w* w+ 11 bitroll-32 prime1 w* ] each
    [ -15 shift ] [ bitxor ] bi prime2 w*
    [ -13 shift ] [ bitxor ] bi prime3 w*
    [ -16 shift ] [ bitxor ] bi ;