forked from batchatco/go-native-netcdf
/
checksum.go
100 lines (83 loc) · 1.5 KB
/
checksum.go
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package hdf5
// Hash function used by HDF5 for checksums (Jenkins lookup3 hash function)
func rot(x uint32, k uint32) uint32 {
return x<<k | x>>(32-k)
}
func mix(a, b, c *uint32) {
*a -= *c
*a ^= rot(*c, 4)
*c += *b
*b -= *a
*b ^= rot(*a, 6)
*a += *c
*c -= *b
*c ^= rot(*b, 8)
*b += *a
*a -= *c
*a ^= rot(*c, 16)
*c += *b
*b -= *a
*b ^= rot(*a, 19)
*a += *c
*c -= *b
*c ^= rot(*b, 4)
*b += *a
}
func final(a, b, c *uint32) {
*c ^= *b
*c -= rot(*b, 14)
*a ^= *c
*a -= rot(*c, 11)
*b ^= *a
*b -= rot(*a, 25)
*c ^= *b
*c -= rot(*b, 16)
*a ^= *c
*a -= rot(*c, 4)
*b ^= *a
*b -= rot(*a, 14)
*c ^= *b
*c -= rot(*b, 24)
}
// Computes the HDF5 checksum on 'vals'. nBytes is the number of signficant bytes in
// 'vals', or 0 to compute it based upon the length of 'vals' (4*len(vals)).
func hashInts(vals []uint32, nBytes uint32) uint32 {
if nBytes == 0 {
nBytes = uint32(4 * len(vals))
}
a := 0xdeadbeef + nBytes
b := a
c := a
for nBytes > 12 {
a += vals[0]
b += vals[1]
c += vals[2]
mix(&a, &b, &c)
vals = vals[3:]
nBytes -= 12
}
switch nBytes {
case 12, 11, 10, 9:
a += vals[0]
b += vals[1]
c += vals[2]
case 8, 7, 6, 5:
a += vals[0]
b += vals[1]
case 4, 3, 2, 1:
a += vals[0]
case 0:
return c
}
final(&a, &b, &c)
return c
}
func fletcher32(vals []uint16) uint32 {
sum1 := uint32(0)
sum2 := uint32(0)
for _, v := range vals {
sum1 = (sum1 + uint32(v)) % 65535
sum2 = (sum2 + sum1) % 65535
}
return (uint32(sum2) << 16) | uint32(sum1)
}