hash.h File Reference

Provides functions and structures for producing likely-to-be-unique hash values for images. More...

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Functions
unsigned int	guac_hash_surface (cairo_surface_t *surface)
	Produces a 24-bit hash value from all pixels of the given surface.
int	guac_surface_cmp (cairo_surface_t *a, cairo_surface_t *b)
	Given two Cairo surfaces, returns zero if the data contained within each is identical, and a positive or negative value if the value of the first is found to be lexically greater or less than the second respectively.

Detailed Description

Provides functions and structures for producing likely-to-be-unique hash values for images.

Function Documentation

guac_hash_surface()

unsigned int guac_hash_surface

(

cairo_surface_t *

surface

)

Produces a 24-bit hash value from all pixels of the given surface.

The surface provided must be RGB or ARGB with each pixel stored in 32 bits. The hashing algorithm used is a variant of the cyclic polynomial rolling hash.

Parameters

surface

The Cairo surface to hash.

Returns

An arbitrary 24-bit unsigned integer value intended to be well distributed across different images.

guac_surface_cmp()

int guac_surface_cmp	(	cairo_surface_t *	a,
		cairo_surface_t *	b )

Given two Cairo surfaces, returns zero if the data contained within each is identical, and a positive or negative value if the value of the first is found to be lexically greater or less than the second respectively.

Parameters

a	The first Cairo surface to compare.
b	The Cairo surface to compare the first surface against.

Returns

Zero if the data contained within each is identical, and a positive or negative value if the value of the first is found to be lexically greater or less than the second respectively.