1 | /* $Id: strhash.h 56290 2015-06-09 14:01:31Z vboxsync $ */
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2 | /** @file
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3 | * IPRT - Internal header containing inline string hashing functions.
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4 | */
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5 |
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6 | /*
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7 | * Copyright (C) 2006-2015 Oracle Corporation
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8 | *
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9 | * This file is part of VirtualBox Open Source Edition (OSE), as
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10 | * available from http://www.virtualbox.org. This file is free software;
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11 | * you can redistribute it and/or modify it under the terms of the GNU
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12 | * General Public License (GPL) as published by the Free Software
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13 | * Foundation, in version 2 as it comes in the "COPYING" file of the
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14 | * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
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15 | * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
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16 | *
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17 | * The contents of this file may alternatively be used under the terms
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18 | * of the Common Development and Distribution License Version 1.0
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19 | * (CDDL) only, as it comes in the "COPYING.CDDL" file of the
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20 | * VirtualBox OSE distribution, in which case the provisions of the
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21 | * CDDL are applicable instead of those of the GPL.
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22 | *
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23 | * You may elect to license modified versions of this file under the
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24 | * terms and conditions of either the GPL or the CDDL or both.
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25 | */
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26 |
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27 | #ifndef ___internal_strhash_h
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28 | #define ___internal_strhash_h
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29 |
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30 | #include <iprt/types.h>
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31 |
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32 |
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33 | /* sdbm:
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34 | This algorithm was created for sdbm (a public-domain reimplementation of
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35 | ndbm) database library. it was found to do well in scrambling bits,
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36 | causing better distribution of the keys and fewer splits. it also happens
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37 | to be a good general hashing function with good distribution. the actual
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38 | function is hash(i) = hash(i - 1) * 65599 + str[i]; what is included below
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39 | is the faster version used in gawk. [there is even a faster, duff-device
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40 | version] the magic constant 65599 was picked out of thin air while
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41 | experimenting with different constants, and turns out to be a prime.
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42 | this is one of the algorithms used in berkeley db (see sleepycat) and
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43 | elsewhere. */
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44 |
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45 | /**
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46 | * Hash string, return hash + length.
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47 | */
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48 | DECLINLINE(uint32_t) sdbm(const char *str, size_t *pcch)
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49 | {
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50 | uint8_t *pu8 = (uint8_t *)str;
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51 | uint32_t hash = 0;
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52 | int c;
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53 |
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54 | while ((c = *pu8++))
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55 | hash = c + (hash << 6) + (hash << 16) - hash;
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56 |
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57 | *pcch = (uintptr_t)pu8 - (uintptr_t)str - 1;
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58 | return hash;
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59 | }
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60 |
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61 |
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62 | /**
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63 | * Hash up to N bytes, return hash + hashed length.
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64 | */
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65 | DECLINLINE(uint32_t) sdbmN(const char *str, size_t cchMax, size_t *pcch)
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66 | {
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67 | uint8_t *pu8 = (uint8_t *)str;
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68 | uint32_t hash = 0;
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69 | int c;
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70 |
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71 | while ((c = *pu8++) && cchMax-- > 0)
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72 | hash = c + (hash << 6) + (hash << 16) - hash;
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73 |
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74 | *pcch = (uintptr_t)pu8 - (uintptr_t)str - 1;
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75 | return hash;
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76 | }
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77 |
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78 |
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79 | /**
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80 | * Incremental hashing.
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81 | */
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82 | DECLINLINE(uint32_t) sdbmInc(const char *str, uint32_t hash)
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83 | {
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84 | uint8_t *pu8 = (uint8_t *)str;
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85 | int c;
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86 |
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87 | while ((c = *pu8++))
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88 | hash = c + (hash << 6) + (hash << 16) - hash;
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89 |
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90 | return hash;
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91 | }
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92 |
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93 | /**
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94 | * Incremental hashing with length limitation.
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95 | */
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96 | DECLINLINE(uint32_t) sdbmIncN(const char *psz, size_t cchMax, uint32_t uHash)
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97 | {
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98 | uint8_t *pu8 = (uint8_t *)psz;
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99 | int c;
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100 |
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101 | while ((c = *pu8++) && cchMax-- > 0)
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102 | uHash = c + (uHash << 6) + (uHash << 16) - uHash;
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103 |
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104 | return uHash;
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105 | }
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106 |
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107 |
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108 | #endif
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109 |
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