siphash.pyx

# Translated from the reference implementation at https://github.com/veorq/SipHash

import cython
from libc.stdint cimport uint8_t, uint32_t, uint64_t

DEF cROUNDS = 2
DEF dROUNDS = 4

cdef inline uint64_t _rotl(uint64_t x, uint64_t b) nogil:
    return (x << b) | (x >> (64 - b))

cdef inline void u32to8_le(uint8_t* p, uint32_t v) nogil:
    p[0] = <uint8_t>(v)
    p[1] = <uint8_t>(v >> 8)
    p[2] = <uint8_t>(v >> 16)
    p[3] = <uint8_t>(v >> 24)

cdef inline void u64to8_le(uint8_t* p, uint64_t v) nogil:
    u32to8_le(p, <uint32_t>v)
    u32to8_le(p + 4, <uint32_t>(v >> 32))

cdef inline uint64_t u8to64_le(uint8_t* p) nogil:
    return (<uint64_t>p[0] |
            <uint64_t>p[1] <<  8 |
            <uint64_t>p[2] << 16 | 
            <uint64_t>p[3] << 24 |
            <uint64_t>p[4] << 32 |
            <uint64_t>p[5] << 40 |
            <uint64_t>p[6] << 48 |
            <uint64_t>p[7] << 56)

cdef inline void _sipround(uint64_t* v0, uint64_t* v1,
                           uint64_t* v2, uint64_t* v3) nogil:
    v0[0] += v1[0]
    v1[0] = _rotl(v1[0], 13)
    v1[0] ^= v0[0]
    v0[0] = _rotl(v0[0], 32)
    v2[0] += v3[0]
    v3[0] = _rotl(v3[0], 16)
    v3[0] ^= v2[0]
    v0[0] += v3[0]
    v3[0] = _rotl(v3[0], 21)
    v3[0] ^= v0[0]
    v2[0] += v1[0]
    v1[0] = _rotl(v1[0], 17)
    v1[0] ^= v2[0]
    v2[0] = _rotl(v2[0], 32)

cpdef uint64_t siphash(bytes data, bytes key) except? 0:
    if len(key) != 16:
        raise ValueError(
            'key should be a 16-byte bytestring, got {!r} (len {})'.format(
                key, len(key)))
    return low_level_siphash(data, len(data), key)

@cython.cdivision(True)
cdef uint64_t low_level_siphash(uint8_t* data, size_t datalen,
                                uint8_t* key) nogil:
    cdef uint64_t v0 = 0x736f6d6570736575ULL
    cdef uint64_t v1 = 0x646f72616e646f6dULL
    cdef uint64_t v2 = 0x6c7967656e657261ULL
    cdef uint64_t v3 = 0x7465646279746573ULL
    cdef uint64_t b
    cdef uint64_t k0 = u8to64_le(key)
    cdef uint64_t k1 = u8to64_le(key + 8)
    cdef uint64_t m
    cdef int i
    cdef uint8_t* end = data + datalen - (datalen % sizeof(uint64_t))
    cdef int left = datalen & 7
    cdef int left_byte

    b = (<uint64_t>datalen) << 56
    v3 ^= k1
    v2 ^= k0
    v1 ^= k1
    v0 ^= k0

    while (data != end):
        m = u8to64_le(data)
        v3 ^= m
        for i in range(cROUNDS):
            _sipround(&v0, &v1, &v2, &v3)
        v0 ^= m

        data += sizeof(uint64_t)

    for i in range(left-1, -1, -1):
        b |= (<uint64_t>data[i]) << (i * 8)

    v3 ^= b

    for i in range(cROUNDS):
        _sipround(&v0, &v1, &v2, &v3)

    v0 ^= b
    v2 ^= 0xff

    for i in range(dROUNDS):
        _sipround(&v0, &v1, &v2, &v3)

    b = v0 ^ v1 ^ v2 ^ v3

    return b

oh this is great! will update in a bit

what do u pass as the key?

According to [the documentation here] for another implementation(https://github.com/zacharyvoase/python-csiphash), the key can be this: b'\x00' * 16
There the key is the first argument, and here the key is the second.