1 | /* Implements a string hashing function. |
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2 | Copyright (C) 1995, 1997 Free Software Foundation, Inc. |
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3 | |
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4 | This program is free software; you can redistribute it and/or modify |
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5 | it under the terms of the GNU General Public License as published by |
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6 | the Free Software Foundation; either version 2, or (at your option) |
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7 | any later version. |
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8 | |
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9 | This program is distributed in the hope that it will be useful, |
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10 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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12 | GNU General Public License for more details. |
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13 | |
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14 | You should have received a copy of the GNU Library General Public |
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15 | License along with the GNU C Library; see the file COPYING.LIB. If not, |
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16 | write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, |
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17 | Boston, MA 02111-1307, USA. */ |
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18 | |
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19 | /* @@ end of prolog @@ */ |
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20 | |
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21 | #ifndef PARAMS |
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22 | # if __STDC__ |
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23 | # define PARAMS(Args) Args |
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24 | # else |
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25 | # define PARAMS(Args) () |
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26 | # endif |
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27 | #endif |
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28 | |
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29 | /* We assume to have `unsigned long int' value with at least 32 bits. */ |
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30 | #define HASHWORDBITS 32 |
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31 | |
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32 | |
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33 | /* Defines the so called `hashpjw' function by P.J. Weinberger |
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34 | [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools, |
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35 | 1986, 1987 Bell Telephone Laboratories, Inc.] */ |
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36 | static unsigned long int hash_string PARAMS ((const char *__str_param)); |
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37 | |
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38 | static inline unsigned long int |
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39 | hash_string (str_param) |
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40 | const char *str_param; |
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41 | { |
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42 | unsigned long int hval, g; |
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43 | const char *str = str_param; |
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44 | |
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45 | /* Compute the hash value for the given string. */ |
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46 | hval = 0; |
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47 | while (*str != '\0') |
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48 | { |
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49 | hval <<= 4; |
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50 | hval += (unsigned long int) *str++; |
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51 | g = hval & ((unsigned long int) 0xf << (HASHWORDBITS - 4)); |
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52 | if (g != 0) |
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53 | { |
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54 | hval ^= g >> (HASHWORDBITS - 8); |
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55 | hval ^= g; |
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56 | } |
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57 | } |
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58 | return hval; |
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59 | } |
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