source-engine/gcsdk/steamextra/tier1/pearsonshash.h

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2020-04-22 16:56:21 +00:00
//========= Copyright Valve Corporation, All rights reserved. ============//
//
// Purpose: PearsonsHash.h
//
// This file contains implementation definitions of 'Pearson's' Hash'
// The generic implementation is a template, plus a couple of specializations
// for commonly used types.
//
// Take a look at http://en.wikipedia.org/wiki/Pearson_hashing for more info.
//
//=============================================================================
#ifndef _PEARSONSHASH_H_
#define _PEARSONSHASH_H_
#if defined(_WIN32) || defined(_WIN64)
#pragma once
#endif
extern const unsigned char g_CTHashRandomValues[256] ;
template<typename T>
struct PearsonsHashFunctor
{
typedef uint32 TargetType ;
TargetType operator()(const T& unKey) const
{
// This is a pearsons hash variant that returns a maximum of 32 bits
size_t size = sizeof(T);
const uint8 * k = (const uint8 *) &unKey;
uint32 byte_one = 0, byte_two = 0, byte_three = 0, byte_four = 0, n;
while (size)
{
--size;
n = *k++;
byte_one = g_CTHashRandomValues[byte_one ^ n];
if (size)
{
--size;
n = *k++;
byte_two = g_CTHashRandomValues[byte_two ^ n];
}
else
break;
if (size)
{
--size;
n = *k++;
byte_three = g_CTHashRandomValues[byte_three ^ n];
}
else
break;
if (size)
{
--size;
n = *k++;
byte_four = g_CTHashRandomValues[byte_four ^ n];
}
else
break;
}
TargetType idx = ( byte_four << 24 ) | ( byte_three << 16 ) | ( byte_two << 8 ) | byte_one;
return ( idx );
}
};
//
// We use this specialization for pointer types - it allows somebody
// to define a specialization for some complicated type, and then use a
// pointer to that type as a key, and have that automatically go to the
// specialization for the complicated type !
//
template<typename T>
struct PearsonsHashFunctor<T*>
{
typedef uint32 TargetType ;
TargetType operator()(const T* key) const
{
PearsonsHashFunctor<T> functor ;
return functor(*key) ;
}
};
//
// This functor specializes for unsigned 32 bit integers, a commonly used type in Steam.
// It should return the exact same result as the unspecialized version on Intel Architecture machines.
//
template<>
struct PearsonsHashFunctor<uint32>
{
typedef uint32 TargetType ;
TargetType operator()(const uint32 unKey) const
{
uint32 byte_one = g_CTHashRandomValues[(unKey>>0) & 0xff];
uint32 byte_two = g_CTHashRandomValues[(unKey>>8) & 0xff];
uint32 byte_three = g_CTHashRandomValues[(unKey>>16) & 0xff];
uint32 byte_four = g_CTHashRandomValues[(unKey>>24)&0xff];
return ( byte_four << 24 ) | ( byte_three << 16 ) | ( byte_two << 8 ) | byte_one;
}
};
//
// This functor specializes for unsigned 64 bit integers, another commonly used type in Steam.
// It should return the exact same result as the unspecialized version on Intel Architecture machines.
//
template<>
struct PearsonsHashFunctor<uint64>
{
typedef uint32 TargetType ;
TargetType operator()(const uint64 unKey) const
{
//
// Note that we pull apart the 64 bits in Intel's endian order.
//
uint32 n;
//
// On Intel Machines, to make this return the exact same result as the generic version
// we have to go from least significant byte to most significant byte !
//
n = static_cast<uint32>((unKey >> (0)) & 0xff) ;
uint32 byte_one = g_CTHashRandomValues[n];
n = static_cast<uint32>((unKey >> (8)) & 0xff) ;
uint32 byte_two = g_CTHashRandomValues[n];
n = static_cast<uint32>((unKey >> (16)) & 0xff) ;
uint32 byte_three = g_CTHashRandomValues[n];
n = static_cast<uint32>((unKey >> (24)) & 0xff) ;
uint32 byte_four = g_CTHashRandomValues[n];
n = static_cast<uint32>((unKey >> (32)) & 0xff) ;
byte_one = g_CTHashRandomValues[n ^ byte_one];
n = static_cast<uint32>((unKey >> (8+32)) & 0xff) ;
byte_two = g_CTHashRandomValues[n ^ byte_two];
n = static_cast<uint32>((unKey >> (16+32)) & 0xff) ;
byte_three = g_CTHashRandomValues[n ^ byte_three];
n = static_cast<uint32>((unKey >> (24+32)) & 0xff) ;
byte_four = g_CTHashRandomValues[n ^ byte_four];
return ( byte_four << 24 ) | ( byte_three << 16 ) | ( byte_two << 8 ) | byte_one;
}
};
//
// This functor specializes for C standard NULL terminated strings !
// It is setup so that if you had a char array containing a NULL terminated string
// and correctly sized, ie char rgch[16] = { "123456789012345" } and a
// null terminated string i.e. char *sz = "123456789012345" these will return identical
// results, and both include the NULL terminator in the hash calculation.
//
template<>
struct PearsonsHashFunctor<char*>
{
typedef uint32 TargetType ;
TargetType operator()(const char* szKey) const
{
const uint8 * k = (const uint8 *) szKey ;
uint32 byte_one = 0, byte_two = 0, byte_three = 0, byte_four = 0, n;
do
{
n = *k++;
byte_one = g_CTHashRandomValues[byte_one ^ n];
if (n=='\0')
break;
n = *k++;
byte_two = g_CTHashRandomValues[byte_two ^ n];
if (n=='\0')
break;
n = *k++;
byte_three = g_CTHashRandomValues[byte_three ^ n];
if (n=='\0')
break;
n = *k++;
byte_four = g_CTHashRandomValues[byte_four ^ n];
} while(n!='\0') ;
TargetType idx = ( byte_four << 24 ) | ( byte_three << 16 ) | ( byte_two << 8 ) | byte_one;
return ( idx );
}
};
//
// This functor compares two objects of a particular type and returns a result
// that follows the strcmp/memcmp.
// If the type doesn't provide an operator== or operator< then you can provide
// a type specific specialization to override this defualt functor !
//
template<typename T>
struct ComparisonFunctor
{
int operator()(const T &lhs, const T &rhs) const
{
if( lhs == rhs )
return 0 ;
else if( lhs < rhs )
return -1 ;
else
return 1 ;
}
};
//
// I expect people to build Comparison specializations for full types,
// not pointer types - this Specialization should allow the C++ compiler
// to bind to a specialization for a particular type.
// We do not want to compare pointers for equality, and a memcmp() may
// not be good for a complicated type !
//
template<typename T>
struct ComparisonFunctor<T*>
{
int operator()(const T *lhs, const T *rhs) const
{
ComparisonFunctor<T> functor ;
return functor(*lhs, *rhs) ;
}
};
template<>
struct ComparisonFunctor<int>
{
int operator()(const int lhs, const int rhs) const
{
return lhs-rhs ;
}
};
template<>
struct ComparisonFunctor<unsigned int>
{
int operator()(const unsigned int lhs, const unsigned int rhs) const
{
return static_cast<int>(lhs) - static_cast<int>(rhs) ;
}
};
template<>
struct ComparisonFunctor<uint64>
{
int operator()(const uint64 lhs, const uint64 rhs) const
{
if( lhs < rhs )
return -1 ;
else if( lhs == rhs )
return 0 ;
else
return 1 ;
}
};
template<>
struct ComparisonFunctor<char*>
{
int operator()(const char * lhs, const char* rhs) const
{
return Q_strcmp(lhs, rhs) ;
}
};
#endif // _PEARSONSHASH_H_