43 lines
1.4 KiB
C
43 lines
1.4 KiB
C
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#include <stasis/crc32.h>
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#include <stasis/common.h>
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#ifndef __HASH_H
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#define __HASH_H
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static inline unsigned long stasis_util_two_to_the (char x) {
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return (1 << ((long)x));
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}
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uint32_t logBase2(uint64_t value);
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/**
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This function maps from the length of the bucket list to a appropriate set
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of linear hash parameters to fill that size.
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*/
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static inline void stasis_linear_hash_get_size_params(uint64_t desiredSize,
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unsigned char * tableBits, uint64_t* nextExtension) {
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*tableBits = logBase2(desiredSize)+1;
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*nextExtension = ((desiredSize) - stasis_util_two_to_the(*tableBits-1));
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}
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/**
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@todo despite it's interface, stasis_linear_hash can't return values > 2^32!
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*/
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static inline uint64_t stasis_linear_hash(const void * val, uint64_t val_length,
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unsigned char tableBits, uint64_t nextExtension) {
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// Calculate the hash value as it was before this round of splitting.
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unsigned int oldTableLength = stasis_util_two_to_the(tableBits - 1);
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unsigned int unmixed = stasis_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 = stasis_util_two_to_the(tableBits);
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ret = unmixed & (tableLength - 1);
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}
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return ret;
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}
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#endif /*__HASH_H */
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