121 lines
3.5 KiB
C
121 lines
3.5 KiB
C
#include <lladd/hash.h>
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#include <assert.h>
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//#include <stdio.h>
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/**
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@todo Make hash.c 32/64bit little/big-endian clean...
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*/
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#ifdef THOMAS_WANG_32
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static int thomasWangs32BitMixFunction(int key)
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{
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key += ~(key << 15);
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key ^= (key >> 10);
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key += (key << 3);
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key ^= (key >> 6);
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key += ~(key << 11);
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key ^= (key >> 16);
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return key;
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}
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#else
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#ifdef THOMAS_WANG_64
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static unsigned long thomasWangs64BitMixFunction(unsigned long key)
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{
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key += ~(key << 32L);
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key ^= (key >> 22L);
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key += ~(key << 13L);
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key ^= (key >> 8L);
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key += (key << 3L);
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key ^= (key >> 15L);
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key += ~(key << 27L);
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key ^= (key >> 31L);
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return key;
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}
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#endif
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#endif
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unsigned int max_bucket(unsigned char tableBits, unsigned int nextExtension) {
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unsigned int oldTableLength = twoToThe(tableBits - 1);
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return oldTableLength + nextExtension - 1;
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}
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void hashGetParamsForSize(unsigned int desiredSize,
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unsigned char * tableBits, unsigned int* nextExtension) {
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*tableBits = logBase2(desiredSize)+1;
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*nextExtension = ((desiredSize) - twoToThe(*tableBits-1));
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}
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unsigned int hash(const void * val, long val_length,
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unsigned char tableBits, unsigned int nextExtension) {
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// Calculate the hash value as it was before this round of splitting.
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unsigned int oldTableLength = twoToThe(tableBits - 1);
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unsigned int unmixed = crc32(val, val_length, (unsigned int)-1);
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unsigned int ret = unmixed & (oldTableLength - 1);
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// If the hash value is before the point in this round where we've split,
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// use the new value instead. (The new value may be the same as the
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// old value.)
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if(ret < nextExtension) { /* Might be too low. */
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unsigned int tableLength = twoToThe(tableBits);
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ret = unmixed & (tableLength - 1);
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}
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// printf("ret = %d, bits = %d, nextExt = %d\n", ret, tableBits, nextExtension);
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// fflush(stdout);
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// assert(ret >= 0 && ret < nextExtension - 1);
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return ret;
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}
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static const char LogTable256[] =
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{
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0, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
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4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
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5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
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5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
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6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
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6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
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6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
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6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7
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};
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/*Taken from
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http://graphics.stanford.edu/~seander/bithacks.html
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@todo extend to handle unsigned long (this will mean 64bit on 64bit
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platforms; need compiler macro to test for sizeof(long), test
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harness to compare logBase2Slow's output with logBase2's output,
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etc...)
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*/
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unsigned int logBase2(unsigned int v) {
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unsigned int r = 0; // r will be lg(v)
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register unsigned int t, tt; // temporaries
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if ((tt = v >> 16))
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{
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r = (t = v >> 24) ? 24 + LogTable256[t] : 16 + LogTable256[tt & 0xFF];
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}
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else
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{
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r = (t = v >> 8) ? 8 + LogTable256[t] : LogTable256[v];
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}
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return r;
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}
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unsigned long logBase2Slow(unsigned long v) {
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unsigned long r = 0; // r will be lg(v)
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while (v >>= 1) // unroll for more speed...
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{
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r++;
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}
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return r;
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}
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