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Update H3 documentation (and minor style nits.)

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Matthias Vallentin 2013-06-13 23:12:00 -07:00
parent 529d120376
commit a6d7b7856e
1 changed files with 31 additions and 29 deletions
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60
src/H3.h
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@ -49,9 +49,9 @@
// hash a substring of the data. Hashes of substrings can be bitwise-XOR'ed
// together to get the same result as hashing the full string.
// Any number of hash functions can be created by creating new instances of H3,
// with the same or different template parameters. The hash function is
// randomly generated using bro_random(); you must call init_random_seed()
// before the H3 constructor if you wish to seed it.
// with the same or different template parameters. The hash function
// constructor takes a seed as argument which defaults to a call to
// bro_random().
#ifndef H3_H
@ -62,34 +62,34 @@
// The number of values representable by a byte.
#define H3_BYTE_RANGE (UCHAR_MAX+1)
template<class T, int N> class H3 {
T byte_lookup[N][H3_BYTE_RANGE];
template <typename T, int N>
class H3 {
public:
H3(T seed = bro_random())
H3(T seed = bro_random())
{
T bit_lookup[N * CHAR_BIT];
for ( size_t bit = 0; bit < N * CHAR_BIT; bit++ )
{
T bit_lookup[N * CHAR_BIT];
for ( size_t bit = 0; bit < N * CHAR_BIT; bit++ )
{
bit_lookup[bit] = 0;
for ( size_t i = 0; i < sizeof(T)/2; i++ )
// assume random() returns at least 16 random bits
bit_lookup[bit] = (bit_lookup[bit] << 16) | (seed & 0xFFFF);
}
for ( size_t byte = 0; byte < N; byte++ )
{
for ( unsigned val = 0; val < H3_BYTE_RANGE; val++ )
{
byte_lookup[byte][val] = 0;
for ( size_t bit = 0; bit < CHAR_BIT; bit++ )
// Does this mean byte_lookup[*][0] == 0? -RP
if (val & (1 << bit))
byte_lookup[byte][val] ^= bit_lookup[byte*CHAR_BIT+bit];
}
}
bit_lookup[bit] = 0;
for ( size_t i = 0; i < sizeof(T)/2; i++ )
// assume random() returns at least 16 random bits
bit_lookup[bit] = (bit_lookup[bit] << 16) | (seed & 0xFFFF);
}
for ( size_t byte = 0; byte < N; byte++ )
{
for ( unsigned val = 0; val < H3_BYTE_RANGE; val++ )
{
byte_lookup[byte][val] = 0;
for ( size_t bit = 0; bit < CHAR_BIT; bit++ )
// Does this mean byte_lookup[*][0] == 0? -RP
if (val & (1 << bit))
byte_lookup[byte][val] ^= bit_lookup[byte*CHAR_BIT+bit];
}
}
}
T operator()(const void* data, size_t size, size_t offset = 0) const
{
const unsigned char *p = static_cast<const unsigned char*>(data);
@ -97,7 +97,7 @@ public:
// loop optmized with Duff's Device
register unsigned n = (size + 7) / 8;
switch (size % 8) {
switch ( size % 8 ) {
case 0: do { result ^= byte_lookup[offset++][*p++];
case 7: result ^= byte_lookup[offset++][*p++];
case 6: result ^= byte_lookup[offset++][*p++];
@ -106,11 +106,13 @@ public:
case 3: result ^= byte_lookup[offset++][*p++];
case 2: result ^= byte_lookup[offset++][*p++];
case 1: result ^= byte_lookup[offset++][*p++];
} while (--n > 0);
} while ( --n > 0 );
}
return result;
}
private:
T byte_lookup[N][H3_BYTE_RANGE];
};
#endif //H3_H