gum::HashFuncConst Class Reference

Useful constants for hash functions. More...

#include <agrum/tools/core/hashFunc.h>

Static Public Attributes
static constexpr Size	gold = sizeof(Size) == 4 ? Size(2654435769UL) : Size(11400714819323198486UL)
static constexpr Size	pi = sizeof(Size) == 4 ? Size(3373259426UL) : Size(14488038916154245684UL)
static constexpr Size	mask = sizeof(Size) == 4 ? Size(4294967295UL) : Size(18446744073709551615UL)
static constexpr Size	offset = sizeof(Size) == 4 ? Size(32) : Size(64)

Detailed Description

Useful constants for hash functions.

Hash functions are of the form [M * ((k * A) mod 1)], where [] stands for the integer part, M is equal to the number of slots in the hashtable, k is the key to be hashed, and mod 1 retrieves the decimal part of (k * A). A is an irrational number (currently either the gold number or pi/4). To speed up computations, the hash function is implemented using only Size (a.k.a. std::size_t). Therefore pi/4 and the gold number are encoded as X * 2^{-n} where n is the number of bits in a Size. Consequently, we should adapt X's definition to 32 and 64 bits architectures.

Definition at line 74 of file hashFunc.h.

Member Data Documentation

gold

constexpr Size gum::HashFuncConst::gold = sizeof(Size) == 4 ? Size(2654435769UL) : Size(11400714819323198486UL)

static

Definition at line 76 of file hashFunc.h.

mask

constexpr Size gum::HashFuncConst::mask = sizeof(Size) == 4 ? Size(4294967295UL) : Size(18446744073709551615UL)

static

Definition at line 80 of file hashFunc.h.

offset

constexpr Size gum::HashFuncConst::offset = sizeof(Size) == 4 ? Size(32) : Size(64)

static

Definition at line 81 of file hashFunc.h.

pi

constexpr Size gum::HashFuncConst::pi = sizeof(Size) == 4 ? Size(3373259426UL) : Size(14488038916154245684UL)

static

Definition at line 78 of file hashFunc.h.

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The documentation for this class was generated from the following file:

• agrum/tools/core/hashFunc.h