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_hwi (HOST_WIDE_INT v)
  62   {
  63     val = iterative_hash_host_wide_int (v, val);
  64   }
  65
  66   /* Add wide_int-based value V.  */
  67   template<typename T>
  68   void add_wide_int (const generic_wide_int<T> &x)
  69   {
  70     add_int (x.get_len ());
  71     for (unsigned i = 0; i < x.get_len (); i++)
  72       add_hwi (x.elt (i));
  73   }
  74
  75   /* Hash in pointer PTR.  */
  76   void add_ptr (const void *ptr)
  77   {
  78     add (&ptr, sizeof (ptr));
  79   }
  80
  81   /* Add a memory block DATA with size LEN.  */
  82   void add (const void *data, size_t len)
  83   {
  84     val = iterative_hash (data, len, val);
  85   }
  86
  87   /* Merge hash value OTHER.  */
  88   void merge_hash (hashval_t other)
  89   {
  90     val = iterative_hash_hashval_t (other, val);
  91   }
  92
  93   /* Hash in state from other inchash OTHER.  */
  94   void merge (hash &other)
  95   {
  96     merge_hash (other.val);
  97   }
  98
  99   template<class T> void add_object(T &obj)
 100   {
 101     add (&obj, sizeof(T));
 102   }
 103
 104   /* Support for accumulating boolean flags */
 105
 106   void add_flag (bool flag)
 107   {
 108     bits = (bits << 1) | flag;
 109   }
 110
 111   void commit_flag ()
 112   {
 113     add_int (bits);
 114     bits = 0;
 115   }
 116
 117   /* Support for commutative hashing. Add A and B in a defined order
 118      based on their value. This is useful for hashing commutative
 119      expressions, so that A+B and B+A get the same hash.  */
 120
 121   void add_commutative (hash &a, hash &b)
 122   {
 123     if (a.end() > b.end())
 124       {
 125         merge (b);
 126         merge (a);
 127       }
 128     else
 129       {
 130         merge (a);
 131         merge (b);
 132       }
 133   }
 134
 135  private:
 136   hashval_t val;
 137   unsigned bits;
 138 };
 139
 140 }
 141
 142 /* Borrowed from hashtab.c iterative_hash implementation.  */
 143 #define mix(a,b,c) \
 144 { \
 145   a -= b; a -= c; a ^= (c>>13); \
 146   b -= c; b -= a; b ^= (a<< 8); \
 147   c -= a; c -= b; c ^= ((b&0xffffffff)>>13); \
 148   a -= b; a -= c; a ^= ((c&0xffffffff)>>12); \
 149   b -= c; b -= a; b = (b ^ (a<<16)) & 0xffffffff; \
 150   c -= a; c -= b; c = (c ^ (b>> 5)) & 0xffffffff; \
 151   a -= b; a -= c; a = (a ^ (c>> 3)) & 0xffffffff; \
 152   b -= c; b -= a; b = (b ^ (a<<10)) & 0xffffffff; \
 153   c -= a; c -= b; c = (c ^ (b>>15)) & 0xffffffff; \
 154 }
 155
 156
 157 /* Produce good hash value combining VAL and VAL2.  */
 158 inline
 159 hashval_t
 160 iterative_hash_hashval_t (hashval_t val, hashval_t val2)
 161 {
 162   /* the golden ratio; an arbitrary value.  */
 163   hashval_t a = 0x9e3779b9;
 164
 165   mix (a, val, val2);
 166   return val2;
 167 }
 168
 169 /* Produce good hash value combining VAL and VAL2.  */
 170
 171 inline
 172 hashval_t
 173 iterative_hash_host_wide_int (HOST_WIDE_INT val, hashval_t val2)
 174 {
 175   if (sizeof (HOST_WIDE_INT) == sizeof (hashval_t))
 176     return iterative_hash_hashval_t (val, val2);
 177   else
 178     {
 179       hashval_t a = (hashval_t) val;
 180       /* Avoid warnings about shifting of more than the width of the type on
 181          hosts that won't execute this path.  */
 182       int zero = 0;
 183       hashval_t b = (hashval_t) (val >> (sizeof (hashval_t) * 8 + zero));
 184       mix (a, b, val2);
 185       if (sizeof (HOST_WIDE_INT) > 2 * sizeof (hashval_t))
 186         {
 187           hashval_t a = (hashval_t) (val >> (sizeof (hashval_t) * 16 + zero));
 188           hashval_t b = (hashval_t) (val >> (sizeof (hashval_t) * 24 + zero));
 189           mix (a, b, val2);
 190         }
 191       return val2;
 192     }
 193 }
 194
 195 #endif