modules/up/src/Core/gnu/hash.cc

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FUNCTIONS

This source file includes following functions.
  1. hashpjw
  2. multiplicativehash
  3. foldhash

   1 /* 
   2 Copyright (C) 1990 Free Software Foundation
   3     written by Doug Lea (dl@rocky.oswego.edu)
   4 
   5 This file is part of the GNU C++ Library.  This library is free
   6 software; you can redistribute it and/or modify it under the terms of
   7 the GNU Library General Public License as published by the Free
   8 Software Foundation; either version 2 of the License, or (at your
   9 option) any later version.  This library is distributed in the hope
  10 that it will be useful, but WITHOUT ANY WARRANTY; without even the
  11 implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
  12 PURPOSE.  See the GNU Library General Public License for more details.
  13 You should have received a copy of the GNU Library General Public
  14 License along with this library; if not, write to the Free Software
  15 Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  16 */
  17 
  18 #ifdef __GNUG__
  19 #pragma implementation
  20 #endif
  21 
  22 /*
  23  some useful hash functions
  24 */
  25 
  26 unsigned int hashpjw(const char* x) // From Dragon book, p436
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  27 {
  28   unsigned int h = 0;
  29   unsigned int g;
  30 
  31   while (*x != 0)
  32   {
  33     h = (h << 4) + *x++;
  34     if ((g = h & 0xf0000000) != 0)
  35       h = (h ^ (g >> 24)) ^ g;
  36   }
  37   return h;
  38 }
  39 
  40 unsigned int multiplicativehash(int x)
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  41 {
  42   // uses a const close to golden ratio * pow(2,32)
  43   return ((unsigned)x) * 2654435767u;
  44 }
  45 
  46 
  47 unsigned int foldhash(double x)
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  48 {
  49   union { unsigned int i[2]; double d; } u;
  50   u.d = x;
  51   unsigned int u0 = u.i[0];
  52   unsigned int u1 = u.i[1]; 
  53   return u0 ^ u1;
  54 }
  55 

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