mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-01 12:01:58 +00:00
232 lines
8.3 KiB
C++
232 lines
8.3 KiB
C++
// Modified by Russ Cox to add "namespace re2".
|
|
// Also threw away all but hashword and hashword2.
|
|
// http://burtleburtle.net/bob/c/lookup3.c
|
|
|
|
/*
|
|
-------------------------------------------------------------------------------
|
|
lookup3.c, by Bob Jenkins, May 2006, Public Domain.
|
|
|
|
These are functions for producing 32-bit hashes for hash table lookup.
|
|
hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
|
|
are externally useful functions. Routines to test the hash are included
|
|
if SELF_TEST is defined. You can use this free for any purpose. It's in
|
|
the public domain. It has no warranty.
|
|
|
|
You probably want to use hashlittle(). hashlittle() and hashbig()
|
|
hash byte arrays. hashlittle() is is faster than hashbig() on
|
|
little-endian machines. Intel and AMD are little-endian machines.
|
|
On second thought, you probably want hashlittle2(), which is identical to
|
|
hashlittle() except it returns two 32-bit hashes for the price of one.
|
|
You could implement hashbig2() if you wanted but I haven't bothered here.
|
|
|
|
If you want to find a hash of, say, exactly 7 integers, do
|
|
a = i1; b = i2; c = i3;
|
|
mix(a,b,c);
|
|
a += i4; b += i5; c += i6;
|
|
mix(a,b,c);
|
|
a += i7;
|
|
final(a,b,c);
|
|
then use c as the hash value. If you have a variable length array of
|
|
4-byte integers to hash, use hashword(). If you have a byte array (like
|
|
a character string), use hashlittle(). If you have several byte arrays, or
|
|
a mix of things, see the comments above hashlittle().
|
|
|
|
Why is this so big? I read 12 bytes at a time into 3 4-byte integers,
|
|
then mix those integers. This is fast (you can do a lot more thorough
|
|
mixing with 12*3 instructions on 3 integers than you can with 3 instructions
|
|
on 1 byte), but shoehorning those bytes into integers efficiently is messy.
|
|
-------------------------------------------------------------------------------
|
|
*/
|
|
|
|
#include "util/util.h"
|
|
|
|
#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
|
|
|
|
/*
|
|
-------------------------------------------------------------------------------
|
|
mix -- mix 3 32-bit values reversibly.
|
|
|
|
This is reversible, so any information in (a,b,c) before mix() is
|
|
still in (a,b,c) after mix().
|
|
|
|
If four pairs of (a,b,c) inputs are run through mix(), or through
|
|
mix() in reverse, there are at least 32 bits of the output that
|
|
are sometimes the same for one pair and different for another pair.
|
|
This was tested for:
|
|
* pairs that differed by one bit, by two bits, in any combination
|
|
of top bits of (a,b,c), or in any combination of bottom bits of
|
|
(a,b,c).
|
|
* "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
|
|
the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
|
|
is commonly produced by subtraction) look like a single 1-bit
|
|
difference.
|
|
* the base values were pseudorandom, all zero but one bit set, or
|
|
all zero plus a counter that starts at zero.
|
|
|
|
Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
|
|
satisfy this are
|
|
4 6 8 16 19 4
|
|
9 15 3 18 27 15
|
|
14 9 3 7 17 3
|
|
Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing
|
|
for "differ" defined as + with a one-bit base and a two-bit delta. I
|
|
used http://burtleburtle.net/bob/hash/avalanche.html to choose
|
|
the operations, constants, and arrangements of the variables.
|
|
|
|
This does not achieve avalanche. There are input bits of (a,b,c)
|
|
that fail to affect some output bits of (a,b,c), especially of a. The
|
|
most thoroughly mixed value is c, but it doesn't really even achieve
|
|
avalanche in c.
|
|
|
|
This allows some parallelism. Read-after-writes are good at doubling
|
|
the number of bits affected, so the goal of mixing pulls in the opposite
|
|
direction as the goal of parallelism. I did what I could. Rotates
|
|
seem to cost as much as shifts on every machine I could lay my hands
|
|
on, and rotates are much kinder to the top and bottom bits, so I used
|
|
rotates.
|
|
-------------------------------------------------------------------------------
|
|
*/
|
|
#define mix(a,b,c) \
|
|
{ \
|
|
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; \
|
|
}
|
|
|
|
/*
|
|
-------------------------------------------------------------------------------
|
|
final -- final mixing of 3 32-bit values (a,b,c) into c
|
|
|
|
Pairs of (a,b,c) values differing in only a few bits will usually
|
|
produce values of c that look totally different. This was tested for
|
|
* pairs that differed by one bit, by two bits, in any combination
|
|
of top bits of (a,b,c), or in any combination of bottom bits of
|
|
(a,b,c).
|
|
* "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
|
|
the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
|
|
is commonly produced by subtraction) look like a single 1-bit
|
|
difference.
|
|
* the base values were pseudorandom, all zero but one bit set, or
|
|
all zero plus a counter that starts at zero.
|
|
|
|
These constants passed:
|
|
14 11 25 16 4 14 24
|
|
12 14 25 16 4 14 24
|
|
and these came close:
|
|
4 8 15 26 3 22 24
|
|
10 8 15 26 3 22 24
|
|
11 8 15 26 3 22 24
|
|
-------------------------------------------------------------------------------
|
|
*/
|
|
#define final(a,b,c) \
|
|
{ \
|
|
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); \
|
|
}
|
|
|
|
namespace re2 {
|
|
|
|
/*
|
|
--------------------------------------------------------------------
|
|
This works on all machines. To be useful, it requires
|
|
-- that the key be an array of uint32_t's, and
|
|
-- that the length be the number of uint32_t's in the key
|
|
|
|
The function hashword() is identical to hashlittle() on little-endian
|
|
machines, and identical to hashbig() on big-endian machines,
|
|
except that the length has to be measured in uint32_ts rather than in
|
|
bytes. hashlittle() is more complicated than hashword() only because
|
|
hashlittle() has to dance around fitting the key bytes into registers.
|
|
--------------------------------------------------------------------
|
|
*/
|
|
uint32 hashword(
|
|
const uint32 *k, /* the key, an array of uint32_t values */
|
|
size_t length, /* the length of the key, in uint32_ts */
|
|
uint32 initval) /* the previous hash, or an arbitrary value */
|
|
{
|
|
uint32_t a,b,c;
|
|
|
|
/* Set up the internal state */
|
|
a = b = c = 0xdeadbeef + (((uint32_t)length)<<2) + initval;
|
|
|
|
/*------------------------------------------------- handle most of the key */
|
|
while (length > 3)
|
|
{
|
|
a += k[0];
|
|
b += k[1];
|
|
c += k[2];
|
|
mix(a,b,c);
|
|
length -= 3;
|
|
k += 3;
|
|
}
|
|
|
|
/*------------------------------------------- handle the last 3 uint32_t's */
|
|
switch(length) /* all the case statements fall through */
|
|
{
|
|
case 3 : c+=k[2];
|
|
case 2 : b+=k[1];
|
|
case 1 : a+=k[0];
|
|
final(a,b,c);
|
|
case 0: /* case 0: nothing left to add */
|
|
break;
|
|
}
|
|
/*------------------------------------------------------ report the result */
|
|
return c;
|
|
}
|
|
|
|
|
|
/*
|
|
--------------------------------------------------------------------
|
|
hashword2() -- same as hashword(), but take two seeds and return two
|
|
32-bit values. pc and pb must both be nonnull, and *pc and *pb must
|
|
both be initialized with seeds. If you pass in (*pb)==0, the output
|
|
(*pc) will be the same as the return value from hashword().
|
|
--------------------------------------------------------------------
|
|
*/
|
|
void hashword2 (
|
|
const uint32 *k, /* the key, an array of uint32_t values */
|
|
size_t length, /* the length of the key, in uint32_ts */
|
|
uint32 *pc, /* IN: seed OUT: primary hash value */
|
|
uint32 *pb) /* IN: more seed OUT: secondary hash value */
|
|
{
|
|
uint32_t a,b,c;
|
|
|
|
/* Set up the internal state */
|
|
a = b = c = 0xdeadbeef + ((uint32_t)(length<<2)) + *pc;
|
|
c += *pb;
|
|
|
|
/*------------------------------------------------- handle most of the key */
|
|
while (length > 3)
|
|
{
|
|
a += k[0];
|
|
b += k[1];
|
|
c += k[2];
|
|
mix(a,b,c);
|
|
length -= 3;
|
|
k += 3;
|
|
}
|
|
|
|
/*------------------------------------------- handle the last 3 uint32_t's */
|
|
switch(length) /* all the case statements fall through */
|
|
{
|
|
case 3 : c+=k[2];
|
|
case 2 : b+=k[1];
|
|
case 1 : a+=k[0];
|
|
final(a,b,c);
|
|
case 0: /* case 0: nothing left to add */
|
|
break;
|
|
}
|
|
/*------------------------------------------------------ report the result */
|
|
*pc=c; *pb=b;
|
|
}
|
|
|
|
} // namespace re2
|