in java/core/src/java/org/apache/orc/util/CuckooSetBytes.java [287:463]
private int hash(byte[] key, int start, int nbytes, int initval) {
int length = nbytes;
long a, b, c; // We use longs because we don't have unsigned ints
a = b = c = (0x00000000deadbeefL + length + initval) & INT_MASK;
int offset = start;
for (; length > 12; offset += 12, length -= 12) {
a = (a + (key[offset] & BYTE_MASK)) & INT_MASK;
a = (a + (((key[offset + 1] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
a = (a + (((key[offset + 2] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
a = (a + (((key[offset + 3] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
b = (b + (key[offset + 4] & BYTE_MASK)) & INT_MASK;
b = (b + (((key[offset + 5] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
b = (b + (((key[offset + 6] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
b = (b + (((key[offset + 7] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
c = (c + (key[offset + 8] & BYTE_MASK)) & INT_MASK;
c = (c + (((key[offset + 9] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
c = (c + (((key[offset + 10] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
c = (c + (((key[offset + 11] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
/*
* 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; \
* }
*
* mix(a,b,c);
*/
a = (a - c) & INT_MASK;
a ^= rot(c, 4);
c = (c + b) & INT_MASK;
b = (b - a) & INT_MASK;
b ^= rot(a, 6);
a = (a + c) & INT_MASK;
c = (c - b) & INT_MASK;
c ^= rot(b, 8);
b = (b + a) & INT_MASK;
a = (a - c) & INT_MASK;
a ^= rot(c,16);
c = (c + b) & INT_MASK;
b = (b - a) & INT_MASK;
b ^= rot(a,19);
a = (a + c) & INT_MASK;
c = (c - b) & INT_MASK;
c ^= rot(b, 4);
b = (b + a) & INT_MASK;
}
//-------------------------------- last block: affect all 32 bits of (c)
switch (length) { // all the case statements fall through
case 12:
c = (c + (((key[offset + 11] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
case 11:
c = (c + (((key[offset + 10] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
case 10:
c = (c + (((key[offset + 9] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
case 9:
c = (c + (key[offset + 8] & BYTE_MASK)) & INT_MASK;
case 8:
b = (b + (((key[offset + 7] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
case 7:
b = (b + (((key[offset + 6] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
case 6:
b = (b + (((key[offset + 5] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
case 5:
b = (b + (key[offset + 4] & BYTE_MASK)) & INT_MASK;
case 4:
a = (a + (((key[offset + 3] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
case 3:
a = (a + (((key[offset + 2] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
case 2:
a = (a + (((key[offset + 1] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
case 1:
a = (a + (key[offset] & BYTE_MASK)) & INT_MASK;
break;
case 0:
return (int)(c & INT_MASK);
}
/*
* 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); \
* }
*
*/
c ^= b;
c = (c - rot(b,14)) & INT_MASK;
a ^= c;
a = (a - rot(c,11)) & INT_MASK;
b ^= a;
b = (b - rot(a,25)) & INT_MASK;
c ^= b;
c = (c - rot(b,16)) & INT_MASK;
a ^= c;
a = (a - rot(c,4)) & INT_MASK;
b ^= a;
b = (b - rot(a,14)) & INT_MASK;
c ^= b;
c = (c - rot(b,24)) & INT_MASK;
return (int)(c & INT_MASK);
}