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"""
Implementation of Postgres hashing function.
hashtext_old() - used up to PostgreSQL 8.3
hashtext_new() - used since PostgreSQL 8.4
>>> import skytools._chashtext
>>> for i in range(3):
... print [hashtext_new_py('x' * (i*5 + j)) for j in range(5)]
[-1477818771, 1074944137, -1086392228, -1992236649, -1379736791]
[-370454118, 1489915569, -66683019, -2126973000, 1651296771]
[755764456, -1494243903, 631527812, 28686851, -9498641]
>>> for i in range(3):
... print [hashtext_old_py('x' * (i*5 + j)) for j in range(5)]
[-863449762, 37835117, 294739542, -320432768, 1007638138]
[1422906842, -261065348, 59863994, -162804943, 1736144510]
[-682756517, 317827663, -495599455, -1411793989, 1739997714]
>>> data = 'HypficUjFitraxlumCitcemkiOkIkthi'
>>> p = [hashtext_old_py(data[:l]) for l in range(len(data)+1)]
>>> c = [hashtext_old(data[:l]) for l in range(len(data)+1)]
>>> assert p == c, '%s <> %s' % (p, c)
>>> p == c
True
>>> p = [hashtext_new_py(data[:l]) for l in range(len(data)+1)]
>>> c = [hashtext_new(data[:l]) for l in range(len(data)+1)]
>>> assert p == c, '%s <> %s' % (p, c)
>>> p == c
True
"""
import sys, struct
__all__ = ["hashtext_old", "hashtext_new"]
# pad for last partial block
PADDING = '\0' * 12
def uint32(x):
"""python does not have 32 bit integer so we need this hack to produce uint32 after bit operations"""
return x & 0xffffffff
#
# Old Postgres hashtext() - lookup2 with custom initval
#
FMT_OLD = struct.Struct("<LLL")
def mix_old(a,b,c):
c = uint32(c)
a -= b; a -= c; a = uint32(a ^ (c>>13))
b -= c; b -= a; b = uint32(b ^ (a<<8))
c -= a; c -= b; c = uint32(c ^ (b>>13))
a -= b; a -= c; a = uint32(a ^ (c>>12))
b -= c; b -= a; b = uint32(b ^ (a<<16))
c -= a; c -= b; c = uint32(c ^ (b>>5))
a -= b; a -= c; a = uint32(a ^ (c>>3))
b -= c; b -= a; b = uint32(b ^ (a<<10))
c -= a; c -= b; c = uint32(c ^ (b>>15))
return a, b, c
def hashtext_old_py(k):
"""Old Postgres hashtext()"""
remain = len(k)
pos = 0
a = b = 0x9e3779b9
c = 3923095
# handle most of the key
while remain >= 12:
a2, b2, c2 = FMT_OLD.unpack_from(k, pos)
a, b, c = mix_old(a + a2, b + b2, c + c2)
pos += 12;
remain -= 12;
# handle the last 11 bytes
a2, b2, c2 = FMT_OLD.unpack_from(k[pos:] + PADDING, 0)
# the lowest byte of c is reserved for the length
c2 = (c2 << 8) + len(k)
a, b, c = mix_old(a + a2, b + b2, c + c2)
# convert to signed int
if (c & 0x80000000):
c = -0x100000000 + c
return int(c)
#
# New Postgres hashtext() - hacked lookup3:
# - custom initval
# - calls mix() when len=12
# - shifted c in last block on little-endian
#
FMT_NEW = struct.Struct("=LLL")
def rol32(x,k):
return (((x)<<(k)) | (uint32(x)>>(32-(k))))
def mix_new(a,b,c):
a -= c; a ^= rol32(c, 4); c += b
b -= a; b ^= rol32(a, 6); a += c
c -= b; c ^= rol32(b, 8); b += a
a -= c; a ^= rol32(c,16); c += b
b -= a; b ^= rol32(a,19); a += c
c -= b; c ^= rol32(b, 4); b += a
return uint32(a), uint32(b), uint32(c)
def final_new(a,b,c):
c ^= b; c -= rol32(b,14)
a ^= c; a -= rol32(c,11)
b ^= a; b -= rol32(a,25)
c ^= b; c -= rol32(b,16)
a ^= c; a -= rol32(c, 4)
b ^= a; b -= rol32(a,14)
c ^= b; c -= rol32(b,24)
return uint32(a), uint32(b), uint32(c)
def hashtext_new_py(k):
"""New Postgres hashtext()"""
remain = len(k)
pos = 0
a = b = c = 0x9e3779b9 + len(k) + 3923095
# handle most of the key
while remain >= 12:
a2, b2, c2 = FMT_NEW.unpack_from(k, pos)
a, b, c = mix_new(a + a2, b + b2, c + c2)
pos += 12;
remain -= 12;
# handle the last 11 bytes
a2, b2, c2 = FMT_NEW.unpack_from(k[pos:] + PADDING, 0)
if sys.byteorder == 'little':
c2 = c2 << 8
a, b, c = final_new(a + a2, b + b2, c + c2)
# convert to signed int
if (c & 0x80000000):
c = -0x100000000 + c
return int(c)
try:
from skytools._chashtext import hashtext_old, hashtext_new
except ImportError:
hashtext_old = hashtext_old_py
hashtext_new = hashtext_new_py
# run doctest
if __name__ == '__main__':
import doctest
doctest.testmod()
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