hsiehhash32.h File Reference

Paul Hsieh's SuperFastHash implemented as inline functions for 32-bit input datatypes. More...

Functions
static void	hsieh_hash32_init (uint32 *hashp, uint32 nvalues)
	Initialise the hash value for Paul Hsieh's super fast hash function. More...
static void	hsieh_hash32_step (uint32 *hashp, uint32 value)
	Perform one step in Paul Hsieh's super fast hash function, using a 32-bit input value. More...
static void	hsieh_hash32_finish (uint32 *hashp)
	Finish the hashing for Paul Hsieh's super fast hash function. More...

Detailed Description

Paul Hsieh's SuperFastHash implemented as inline functions for 32-bit input datatypes.

This header file should ONLY be included by C files that use this hash function. Header files should not include this, if the hash function is not used by a source file that includes it, there will be warnings about unused static functions.

Function Documentation

hsieh_hash32_finish()

static void hsieh_hash32_finish ( uint32 *  hashp )

inlinestatic

Finish the hashing for Paul Hsieh's super fast hash function.

Parameters

[in,out]

hashp

A pointer to the hash value to finalise. This should have been initialised by calling hsieh_hash32_init(), and values should have been merged by calling hsieh_hash32_step().

The returned hash value is 32 bits and if a smaller range is required it is up to the caller to do either a mod, for general hash table sizes, or a mask to size of the hash table minus one, for hash table sizes that are a power of two.

eg.

hash % size 

For general hash sizes (slower). or

hash & (size - 1) 

For power of two hash sizes.

It is recommended to make your hash table size a power of two.

hsieh_hash32_init()

static void hsieh_hash32_init ( uint32 *  hashp, uint32  nvalues  )

inlinestatic

Initialise the hash value for Paul Hsieh's super fast hash function.

Parameters

[out]	hashp	A pointer to the hash value to initialise.
[in]	nvalues	The number of 32-bit values that will be used to create the hash key.

To create a hash value, this function is called first, followed by nvalues iterations of hsieh_hash32_step(), and then finally hsieh_hash32_finish(). All of these functions are inlined in the caller.

hsieh_hash32_step()

static void hsieh_hash32_step ( uint32 *  hashp, uint32  value  )

inlinestatic

Perform one step in Paul Hsieh's super fast hash function, using a 32-bit input value.

Parameters

[in,out]	hashp	A pointer to the hash value to combine the value with. This should have been initialised by calling hsieh_hash32_init().
[in]	value	A 32-bit value to merge into the hash value.