Murmur3

MurmurHash3 hash function implementation. More...

Files
file	murmur3.h
	Public header for MurmurHash3 hash function implementation.

Functions
struct AVMurMur3 *	av_murmur3_alloc (void)
	Allocate an AVMurMur3 hash context. More...
void	av_murmur3_init_seeded (struct AVMurMur3 *c, uint64_t seed)
	Initialize or reinitialize an AVMurMur3 hash context with a seed. More...
void	av_murmur3_init (struct AVMurMur3 *c)
	Initialize or reinitialize an AVMurMur3 hash context. More...
void	av_murmur3_update (struct AVMurMur3 *c, const uint8_t *src, int len)
	Update hash context with new data. More...
void	av_murmur3_final (struct AVMurMur3 *c, uint8_t dst[16])
	Finish hashing and output digest value. More...

Detailed Description

MurmurHash3 hash function implementation.

MurmurHash3 is a non-cryptographic hash function, of which three incompatible versions were created by its inventor Austin Appleby:

• 32-bit output
• 128-bit output for 32-bit platforms
• 128-bit output for 64-bit platforms

FFmpeg only implements the last variant: 128-bit output designed for 64-bit platforms. Even though the hash function was designed for 64-bit platforms, the function in reality works on 32-bit systems too, only with reduced performance.

By design, MurmurHash3 requires a seed to operate. In response to this, libavutil provides two functions for hash initiation, one that requires a seed (av_murmur3_init_seeded()) and one that uses a fixed arbitrary integer as the seed, and therefore does not (av_murmur3_init()).

To make hashes comparable, you should provide the same seed for all calls to this hash function – if you are supplying one yourself, that is.

Function Documentation

av_murmur3_alloc()

struct AVMurMur3* av_murmur3_alloc

(

void

)

Allocate an AVMurMur3 hash context.

Returns

Uninitialized hash context or NULL in case of error

Definition at line 32 of file murmur3.c.

Referenced by av_hash_alloc(), and main().

av_murmur3_init_seeded()

void av_murmur3_init_seeded	(	struct AVMurMur3 *	c,
		uint64_t	seed
	)

Initialize or reinitialize an AVMurMur3 hash context with a seed.

Parameters

[out]	c	Hash context
[in]	seed	Random seed

See also

av_murmur3_init()

Detailed description on a discussion of seeds for MurmurHash3.

Definition at line 37 of file murmur3.c.

Referenced by av_murmur3_init(), and main().

av_murmur3_init()

void av_murmur3_init

(

struct AVMurMur3 *

c

)

Initialize or reinitialize an AVMurMur3 hash context.

Equivalent to av_murmur3_init_seeded() with a built-in seed.

Parameters

[out]

c

Hash context

See also

av_murmur3_init_seeded()

Detailed description on a discussion of seeds for MurmurHash3.

Definition at line 43 of file murmur3.c.

Referenced by av_hash_init(), and main().

av_murmur3_update()

void av_murmur3_update	(	struct AVMurMur3 *	c,
		const uint8_t *	src,
		int	len
	)

Update hash context with new data.

Parameters

[out]	c	Hash context
[in]	src	Input data to update hash with
[in]	len	Number of bytes to read from src

Definition at line 93 of file murmur3.c.

Referenced by av_hash_update(), and main().

av_murmur3_final()

void av_murmur3_final	(	struct AVMurMur3 *	c,
		uint8_t	dst[16]
	)

Finish hashing and output digest value.

Parameters

[in,out]	c	Hash context
[out]	dst	Buffer where output digest value is stored

Definition at line 145 of file murmur3.c.

Referenced by av_hash_final(), and main().