gcc/inchash.h

   1 /* An incremental hash abstract data type.
   2    Copyright (C) 2014-2017 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING3.  If not see
  18 <http://www.gnu.org/licenses/>.  */
  19
  20 #ifndef INCHASH_H
  21 #define INCHASH_H 1
  22
  23
  24 /* This file implements an incremential hash function ADT, to be used
  25    by code that incrementially hashes a lot of unrelated data
  26    (not in a single memory block) into a single value. The goal
  27    is to make it easy to plug in efficient hash algorithms.
  28    Currently it just implements the plain old jhash based
  29    incremental hash from gcc's tree.c.  */
  30
  31 hashval_t iterative_hash_host_wide_int (HOST_WIDE_INT, hashval_t);
  32 hashval_t iterative_hash_hashval_t (hashval_t, hashval_t);
  33
  34 namespace inchash
  35 {
  36
  37 class hash
  38 {
  39  public:
  40
  41   /* Start incremential hashing, optionally with SEED.  */
  42   hash (hashval_t seed = 0)
  43   {
  44     val = seed;
  45     bits = 0;
  46   }
  47
  48   /* End incremential hashing and provide the final value.  */
  49   hashval_t end ()
  50   {
  51     return val;
  52   }
  53
  54   /* Add unsigned value V.  */
  55   void add_int (unsigned v)
  56   {
  57     val = iterative_hash_hashval_t (v, val);
  58   }
  59
  60   /* Add HOST_WIDE_INT value V.  */
  61   void add_wide_int (HOST_WIDE_INT v)
  62   {
  63     val = iterative_hash_host_wide_int (v, val);
  64   }
  65
  66   /* Hash in pointer PTR.  */
  67   void add_ptr (const void *ptr)
  68   {
  69     add (&ptr, sizeof (ptr));
  70   }
  71
  72   /* Add a memory block DATA with size LEN.  */
  73   void add (const void *data, size_t len)
  74   {
  75     val = iterative_hash (data, len, val);
  76   }
  77
  78   /* Merge hash value OTHER.  */
  79   void merge_hash (hashval_t other)
  80   {
  81     val = iterative_hash_hashval_t (other, val);
  82   }
  83
  84   /* Hash in state from other inchash OTHER.  */
  85   void merge (hash &other)
  86   {
  87     merge_hash (other.val);
  88   }
  89
  90   template<class T> void add_object(T &obj)
  91   {
  92     add (&obj, sizeof(T));
  93   }
  94
  95   /* Support for accumulating boolean flags */
  96
  97   void add_flag (bool flag)
  98   {
  99     bits = (bits << 1) | flag;
 100   }
 101
 102   void commit_flag ()
 103   {
 104     add_int (bits);
 105     bits = 0;
 106   }
 107
 108   /* Support for commutative hashing. Add A and B in a defined order
 109      based on their value. This is useful for hashing commutative
 110      expressions, so that A+B and B+A get the same hash.  */
 111
 112   void add_commutative (hash &a, hash &b)
 113   {
 114     if (a.end() > b.end())
 115       {
 116         merge (b);
 117         merge (a);
 118       }
 119     else
 120       {
 121         merge (a);
 122         merge (b);
 123       }
 124   }
 125
 126  private:
 127   hashval_t val;
 128   unsigned bits;
 129 };
 130
 131 }
 132
 133 /* Borrowed from hashtab.c iterative_hash implementation.  */
 134 #define mix(a,b,c) \
 135 { \
 136   a -= b; a -= c; a ^= (c>>13); \
 137   b -= c; b -= a; b ^= (a<< 8); \
 138   c -= a; c -= b; c ^= ((b&0xffffffff)>>13); \
 139   a -= b; a -= c; a ^= ((c&0xffffffff)>>12); \
 140   b -= c; b -= a; b = (b ^ (a<<16)) & 0xffffffff; \
 141   c -= a; c -= b; c = (c ^ (b>> 5)) & 0xffffffff; \
 142   a -= b; a -= c; a = (a ^ (c>> 3)) & 0xffffffff; \
 143   b -= c; b -= a; b = (b ^ (a<<10)) & 0xffffffff; \
 144   c -= a; c -= b; c = (c ^ (b>>15)) & 0xffffffff; \
 145 }
 146
 147
 148 /* Produce good hash value combining VAL and VAL2.  */
 149 inline
 150 hashval_t
 151 iterative_hash_hashval_t (hashval_t val, hashval_t val2)
 152 {
 153   /* the golden ratio; an arbitrary value.  */
 154   hashval_t a = 0x9e3779b9;
 155
 156   mix (a, val, val2);
 157   return val2;
 158 }
 159
 160 /* Produce good hash value combining VAL and VAL2.  */
 161
 162 inline
 163 hashval_t
 164 iterative_hash_host_wide_int (HOST_WIDE_INT val, hashval_t val2)
 165 {
 166   if (sizeof (HOST_WIDE_INT) == sizeof (hashval_t))
 167     return iterative_hash_hashval_t (val, val2);
 168   else
 169     {
 170       hashval_t a = (hashval_t) val;
 171       /* Avoid warnings about shifting of more than the width of the type on
 172          hosts that won't execute this path.  */
 173       int zero = 0;
 174       hashval_t b = (hashval_t) (val >> (sizeof (hashval_t) * 8 + zero));
 175       mix (a, b, val2);
 176       if (sizeof (HOST_WIDE_INT) > 2 * sizeof (hashval_t))
 177         {
 178           hashval_t a = (hashval_t) (val >> (sizeof (hashval_t) * 16 + zero));
 179           hashval_t b = (hashval_t) (val >> (sizeof (hashval_t) * 24 + zero));
 180           mix (a, b, val2);
 181         }
 182       return val2;
 183     }
 184 }
 185
 186 #endif