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271 lines
6.9 KiB
271 lines
6.9 KiB
/*++
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Copyright (c) 1998-2002 Microsoft Corporation
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Module Name :
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hashfn.h
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Abstract:
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Declares and defines a collection of overloaded hash functions.
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It is strongly suggested that you use these functions with LKRhash.
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Author:
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George V. Reilly (GeorgeRe) 06-Jan-1998
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Environment:
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Win32 - User Mode
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Project:
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Internet Information Server RunTime Library
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Revision History:
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Paul McDaniel (paulmcd) Feb-05-1999 Trimmed for kernel mode
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and C (not C++)
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--*/
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#ifndef __HASHFN_H__
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#define __HASHFN_H__
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#include <math.h>
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#include <limits.h>
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extern WCHAR FastUpcaseChars[256];
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#define UPCASE_UNICODE_CHAR( wc ) \
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(wc < 256 ? FastUpcaseChars[(UCHAR)(wc)] : RtlUpcaseUnicodeChar(wc))
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// Produce a scrambled, randomish number in the range 0 to RANDOM_PRIME-1.
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// Applying this to the results of the other hash functions is likely to
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// produce a much better distribution, especially for the identity hash
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// functions such as Hash(char c), where records will tend to cluster at
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// the low end of the hashtable otherwise. LKRhash applies this internally
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// to all hash signatures for exactly this reason.
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// __inline ULONG
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// HashScramble(ULONG dwHash)
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// {
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// // Here are 10 primes slightly greater than 10^9
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// // 1000000007, 1000000009, 1000000021, 1000000033, 1000000087,
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// // 1000000093, 1000000097, 1000000103, 1000000123, 1000000181.
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//
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// // default value for "scrambling constant"
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// const ULONG RANDOM_CONSTANT = 314159269UL;
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// // large prime number, also used for scrambling
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// const ULONG RANDOM_PRIME = 1000000007UL;
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//
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// return (RANDOM_CONSTANT * dwHash) % RANDOM_PRIME ;
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// }
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//
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// Given M = A % B, A and B unsigned 32-bit integers greater than zero,
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// there are no values of A or B which yield M = 2^32-1. Why? Because
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// M must be less than B.
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// #define HASH_INVALID_SIGNATURE ULONG_MAX
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// No number in 0..2^31-1 maps to this number after it has been
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// scrambled by HashRandomizeBits
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#define HASH_INVALID_SIGNATURE 31678523
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// Faster scrambling function suggested by Eric Jacobsen
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__inline ULONG
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HashRandomizeBits(ULONG dw)
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{
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const ULONG dwLo = ((dw * 1103515245 + 12345) >> 16);
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const ULONG dwHi = ((dw * 69069 + 1) & 0xffff0000);
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const ULONG dw2 = dwHi | dwLo;
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ASSERT(dw2 != HASH_INVALID_SIGNATURE);
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return dw2;
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}
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// Small prime number used as a multiplier in the supplied hash functions
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#define HASH_MULTIPLIER 101
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#undef HASH_SHIFT_MULTIPLY
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#ifdef HASH_SHIFT_MULTIPLY
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// 127 = 2^7 - 1 is prime
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# define HASH_MULTIPLY(dw) (((dw) << 7) - (dw))
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#else
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# define HASH_MULTIPLY(dw) ((dw) * HASH_MULTIPLIER)
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#endif
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// Fast, simple hash function that tends to give a good distribution.
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// Apply HashScramble to the result if you're using this for something
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// other than LKHash.
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__inline ULONG
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HashStringA(
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const char* psz,
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ULONG dwHash)
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{
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// force compiler to use unsigned arithmetic
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const unsigned char* upsz = (const unsigned char*) psz;
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for ( ; *upsz != '\0'; ++upsz)
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dwHash = HASH_MULTIPLY(dwHash) + *upsz;
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return dwHash;
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}
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// Unicode version of above
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__inline ULONG
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HashStringW(
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const wchar_t* pwsz,
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ULONG dwHash)
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{
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for ( ; *pwsz != L'\0'; ++pwsz)
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dwHash = HASH_MULTIPLY(dwHash) + *pwsz;
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return dwHash;
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}
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__inline ULONG
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HashCharW(
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WCHAR UnicodeChar,
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ULONG Hash
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)
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{
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return HASH_MULTIPLY(Hash) + UnicodeChar;
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}
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// Quick-'n'-dirty case-insensitive string hash function.
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// Make sure that you follow up with _stricmp or _mbsicmp. You should
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// also cache the length of strings and check those first. Caching
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// an uppercase version of a string can help too.
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// Again, apply HashScramble to the result if using with something other
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// than LKHash.
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// Note: this is not really adequate for MBCS strings.
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__inline ULONG
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HashStringNoCaseA(
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const char* psz,
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ULONG dwHash)
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{
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const unsigned char* upsz = (const unsigned char*) psz;
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for ( ; *upsz != '\0'; ++upsz)
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dwHash = HASH_MULTIPLY(dwHash)
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+ (*upsz & 0xDF); // strip off lowercase bit
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return dwHash;
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}
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// Unicode version of above
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__inline ULONG
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HashStringNoCaseW(
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const wchar_t* pwsz,
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ULONG dwHash)
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{
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for ( ; *pwsz != L'\0'; ++pwsz)
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dwHash = HASH_MULTIPLY(dwHash) + UPCASE_UNICODE_CHAR(*pwsz);
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return dwHash;
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}
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__inline ULONG
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HashStringsNoCaseW(
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const wchar_t* pwsz1,
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const wchar_t* pwsz2,
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ULONG dwHash)
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{
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for ( ; *pwsz1 != L'\0'; ++pwsz1)
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dwHash = HASH_MULTIPLY(dwHash) + UPCASE_UNICODE_CHAR(*pwsz1);
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for ( ; *pwsz2 != L'\0'; ++pwsz2)
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dwHash = HASH_MULTIPLY(dwHash) + UPCASE_UNICODE_CHAR(*pwsz2);
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return dwHash;
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}
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__inline ULONG
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HashCharNoCaseW(
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WCHAR UnicodeChar,
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ULONG Hash
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)
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{
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return HASH_MULTIPLY(Hash) + UPCASE_UNICODE_CHAR(UnicodeChar);
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}
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// HashBlob returns the hash of a blob of arbitrary binary data.
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//
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// Warning: HashBlob is generally not the right way to hash a class object.
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// Consider:
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// class CFoo {
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// public:
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// char m_ch;
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// double m_d;
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// char* m_psz;
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// };
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//
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// inline ULONG Hash(const CFoo& rFoo)
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// { return HashBlob(&rFoo, sizeof(CFoo)); }
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//
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// This is the wrong way to hash a CFoo for two reasons: (a) there will be
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// a 7-byte gap between m_ch and m_d imposed by the alignment restrictions
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// of doubles, which will be filled with random data (usually non-zero for
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// stack variables), and (b) it hashes the address (rather than the
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// contents) of the string m_psz. Similarly,
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//
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// bool operator==(const CFoo& rFoo1, const CFoo& rFoo2)
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// { return memcmp(&rFoo1, &rFoo2, sizeof(CFoo)) == 0; }
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//
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// does the wrong thing. Much better to do this:
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//
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// ULONG Hash(const CFoo& rFoo)
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// {
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// return HashString(rFoo.m_psz,
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// 37 * Hash(rFoo.m_ch) + Hash(rFoo.m_d));
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// }
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//
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// Again, apply HashScramble if using with something other than LKHash.
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__inline ULONG
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HashBlob(
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PUCHAR pb,
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ULONG cb,
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ULONG dwHash)
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{
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while (cb-- > 0)
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dwHash = HASH_MULTIPLY(dwHash) + *pb++;
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return dwHash;
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}
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// ======= <snip>
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//
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// paulmcd: a bunch snipped due to use of overloading, not allowed in C
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//
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// ======= <snip>
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__inline ULONG HashDouble(double dbl)
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{
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int nExponent;
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double dblMantissa;
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if (dbl == 0.0)
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return 0;
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dblMantissa = frexp(dbl, &nExponent);
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// 0.5 <= |mantissa| < 1.0
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return (ULONG) ((2.0 * fabs(dblMantissa) - 1.0) * UINT_MAX);
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}
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__inline ULONG HashFloat(float f)
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{ return HashDouble((double) f); }
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#endif // __HASHFN_H__
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