285 lines
6.7 KiB
C++
285 lines
6.7 KiB
C++
/*++
|
|
|
|
Copyright (c) 1998-2000 Microsoft Corporation
|
|
|
|
Module Name :
|
|
hashfn.h
|
|
|
|
Abstract:
|
|
Declares and defines a collection of overloaded hash functions.
|
|
It is strongly suggested that you use these functions with LKRHash.
|
|
|
|
Author:
|
|
George V. Reilly (GeorgeRe) 06-Jan-1998
|
|
|
|
Environment:
|
|
Win32 - User Mode
|
|
|
|
Project:
|
|
Internet Information Server RunTime Library
|
|
|
|
Revision History:
|
|
|
|
--*/
|
|
|
|
#ifndef __HASHFN_H__
|
|
#define __HASHFN_H__
|
|
|
|
|
|
#ifdef __HASHFN_NAMESPACE__
|
|
namespace HashFn {
|
|
#endif // __HASHFN_NAMESPACE__
|
|
|
|
// Produce a scrambled, randomish number in the range 0 to RANDOM_PRIME-1.
|
|
// Applying this to the results of the other hash functions is likely to
|
|
// produce a much better distribution, especially for the identity hash
|
|
// functions such as Hash(char c), where records will tend to cluster at
|
|
// the low end of the hashtable otherwise. LKRHash applies this internally
|
|
// to all hash signatures for exactly this reason.
|
|
|
|
inline DWORD
|
|
HashScramble(DWORD dwHash)
|
|
{
|
|
// Here are 10 primes slightly greater than 10^9
|
|
// 1000000007, 1000000009, 1000000021, 1000000033, 1000000087,
|
|
// 1000000093, 1000000097, 1000000103, 1000000123, 1000000181.
|
|
|
|
// default value for "scrambling constant"
|
|
const DWORD RANDOM_CONSTANT = 314159269UL;
|
|
// large prime number, also used for scrambling
|
|
const DWORD RANDOM_PRIME = 1000000007UL;
|
|
|
|
return (RANDOM_CONSTANT * dwHash) % RANDOM_PRIME ;
|
|
}
|
|
|
|
|
|
// Faster scrambling function suggested by Eric Jacobsen
|
|
|
|
inline DWORD
|
|
RandomizeBits(DWORD dw)
|
|
{
|
|
return (((dw * 1103515245 + 12345) >> 16)
|
|
| ((dw * 69069 + 1) & 0xffff0000));
|
|
}
|
|
|
|
|
|
// Small prime number used as a multiplier in the supplied hash functions
|
|
const DWORD HASH_MULTIPLIER = 101;
|
|
|
|
#undef HASH_SHIFT_MULTIPLY
|
|
|
|
#ifdef HASH_SHIFT_MULTIPLY
|
|
# define HASH_MULTIPLY(dw) (((dw) << 5) - (dw))
|
|
#else
|
|
# define HASH_MULTIPLY(dw) ((dw) * HASH_MULTIPLIER)
|
|
#endif
|
|
|
|
// Fast, simple hash function that tends to give a good distribution.
|
|
// Apply HashScramble to the result if you're using this for something
|
|
// other than LKRHash.
|
|
|
|
inline DWORD
|
|
HashString(
|
|
const char* psz,
|
|
DWORD dwHash = 0)
|
|
{
|
|
// force compiler to use unsigned arithmetic
|
|
const unsigned char* upsz = (const unsigned char*) psz;
|
|
|
|
for ( ; *upsz; ++upsz)
|
|
dwHash = HASH_MULTIPLY(dwHash) + *upsz;
|
|
|
|
return dwHash;
|
|
}
|
|
|
|
|
|
// Unicode version of above
|
|
|
|
inline DWORD
|
|
HashString(
|
|
const wchar_t* pwsz,
|
|
DWORD dwHash = 0)
|
|
{
|
|
for ( ; *pwsz; ++pwsz)
|
|
dwHash = HASH_MULTIPLY(dwHash) + *pwsz;
|
|
|
|
return dwHash;
|
|
}
|
|
|
|
|
|
// Quick-'n'-dirty case-insensitive string hash function.
|
|
// Make sure that you follow up with _stricmp or _mbsicmp. You should
|
|
// also cache the length of strings and check those first. Caching
|
|
// an uppercase version of a string can help too.
|
|
// Again, apply HashScramble to the result if using with something other
|
|
// than LKRHash.
|
|
// Note: this is not really adequate for MBCS strings.
|
|
|
|
inline DWORD
|
|
HashStringNoCase(
|
|
const char* psz,
|
|
DWORD dwHash = 0)
|
|
{
|
|
const unsigned char* upsz = (const unsigned char*) psz;
|
|
|
|
for ( ; *upsz; ++upsz)
|
|
dwHash = HASH_MULTIPLY(dwHash)
|
|
+ (*upsz & 0xDF); // strip off lowercase bit
|
|
|
|
return dwHash;
|
|
}
|
|
|
|
|
|
// Unicode version of above
|
|
|
|
inline DWORD
|
|
HashStringNoCase(
|
|
const wchar_t* pwsz,
|
|
DWORD dwHash = 0)
|
|
{
|
|
for ( ; *pwsz; ++pwsz)
|
|
dwHash = HASH_MULTIPLY(dwHash) + (*pwsz & 0xFFDF);
|
|
|
|
return dwHash;
|
|
}
|
|
|
|
|
|
// HashBlob returns the hash of a blob of arbitrary binary data.
|
|
//
|
|
// Warning: HashBlob is generally not the right way to hash a class object.
|
|
// Consider:
|
|
// class CFoo {
|
|
// public:
|
|
// char m_ch;
|
|
// double m_d;
|
|
// char* m_psz;
|
|
// };
|
|
//
|
|
// inline DWORD Hash(const CFoo& rFoo)
|
|
// { return HashBlob(&rFoo, sizeof(CFoo)); }
|
|
//
|
|
// This is the wrong way to hash a CFoo for two reasons: (a) there will be
|
|
// a 7-byte gap between m_ch and m_d imposed by the alignment restrictions
|
|
// of doubles, which will be filled with random data (usually non-zero for
|
|
// stack variables), and (b) it hashes the address (rather than the
|
|
// contents) of the string m_psz. Similarly,
|
|
//
|
|
// bool operator==(const CFoo& rFoo1, const CFoo& rFoo2)
|
|
// { return memcmp(&rFoo1, &rFoo2, sizeof(CFoo)) == 0; }
|
|
//
|
|
// does the wrong thing. Much better to do this:
|
|
//
|
|
// DWORD Hash(const CFoo& rFoo)
|
|
// {
|
|
// return HashString(rFoo.m_psz,
|
|
// HASH_MULTIPLIER * Hash(rFoo.m_ch)
|
|
// + Hash(rFoo.m_d));
|
|
// }
|
|
//
|
|
// Again, apply HashScramble if using with something other than LKRHash.
|
|
|
|
inline DWORD
|
|
HashBlob(
|
|
const void* pv,
|
|
size_t cb,
|
|
DWORD dwHash = 0)
|
|
{
|
|
LPBYTE pb = static_cast<LPBYTE>(const_cast<void*>(pv));
|
|
|
|
while (cb-- > 0)
|
|
dwHash = HASH_MULTIPLY(dwHash) + *pb++;
|
|
|
|
return dwHash;
|
|
}
|
|
|
|
|
|
|
|
//
|
|
// Overloaded hash functions for all the major builtin types.
|
|
// Again, apply HashScramble to result if using with something other than
|
|
// LKRHash.
|
|
//
|
|
|
|
inline DWORD Hash(const char* psz)
|
|
{ return HashString(psz); }
|
|
|
|
inline DWORD Hash(const unsigned char* pusz)
|
|
{ return HashString(reinterpret_cast<const char*>(pusz)); }
|
|
|
|
inline DWORD Hash(const signed char* pssz)
|
|
{ return HashString(reinterpret_cast<const char*>(pssz)); }
|
|
|
|
inline DWORD Hash(const wchar_t* pwsz)
|
|
{ return HashString(pwsz); }
|
|
|
|
inline DWORD
|
|
Hash(
|
|
const GUID* pguid,
|
|
DWORD dwHash = 0)
|
|
{
|
|
DWORD* pdw = reinterpret_cast<DWORD*>(const_cast<GUID*>(pguid));
|
|
|
|
dwHash = HASH_MULTIPLY(dwHash) + *pdw++;
|
|
dwHash = HASH_MULTIPLY(dwHash) + *pdw++;
|
|
dwHash = HASH_MULTIPLY(dwHash) + *pdw++;
|
|
dwHash = HASH_MULTIPLY(dwHash) + *pdw;
|
|
|
|
return dwHash;
|
|
}
|
|
|
|
// Identity hash functions: scalar values map to themselves
|
|
inline DWORD Hash(char c)
|
|
{ return c; }
|
|
|
|
inline DWORD Hash(unsigned char uc)
|
|
{ return uc; }
|
|
|
|
inline DWORD Hash(signed char sc)
|
|
{ return sc; }
|
|
|
|
inline DWORD Hash(short sh)
|
|
{ return sh; }
|
|
|
|
inline DWORD Hash(unsigned short ush)
|
|
{ return ush; }
|
|
|
|
inline DWORD Hash(int i)
|
|
{ return i; }
|
|
|
|
inline DWORD Hash(unsigned int u)
|
|
{ return u; }
|
|
|
|
inline DWORD Hash(long l)
|
|
{ return l; }
|
|
|
|
inline DWORD Hash(unsigned long ul)
|
|
{ return ul; }
|
|
|
|
inline DWORD Hash(float f)
|
|
{
|
|
// be careful of rounding errors when computing keys
|
|
union {
|
|
float f;
|
|
DWORD dw;
|
|
} u;
|
|
u.f = f;
|
|
return u.dw;
|
|
}
|
|
|
|
inline DWORD Hash(double dbl)
|
|
{
|
|
// be careful of rounding errors when computing keys
|
|
union {
|
|
double dbl;
|
|
DWORD dw[2];
|
|
} u;
|
|
u.dbl = dbl;
|
|
return u.dw[0] * HASH_MULTIPLIER + u.dw[1];
|
|
}
|
|
|
|
#ifdef __HASHFN_NAMESPACE__
|
|
}
|
|
#endif // __HASHFN_NAMESPACE__
|
|
|
|
#endif // __HASHFN_H__
|