gcc/inchash.h

   1 /* An incremental hash abstract data type.
   2    Copyright (C) 2014-2015 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 #ifdef GENERATOR_FILE
  24 #include "bconfig.h"
  25 #else
  26 #include "config.h"
  27 #endif
  28 #include "system.h"
  29 #include "coretypes.h"
  30 #include "hashtab.h"
  31
  32 /* This file implements an incremential hash function ADT, to be used
  33    by code that incrementially hashes a lot of unrelated data
  34    (not in a single memory block) into a single value. The goal
  35    is to make it easy to plug in efficient hash algorithms.
  36    Currently it just implements the plain old jhash based
  37    incremental hash from gcc's tree.c.  */
  38
  39 hashval_t iterative_hash_host_wide_int (HOST_WIDE_INT, hashval_t);
  40 hashval_t iterative_hash_hashval_t (hashval_t, hashval_t);
  41
  42 namespace inchash
  43 {
  44
  45 class hash
  46 {
  47  public:
  48
  49   /* Start incremential hashing, optionally with SEED.  */
  50   hash (hashval_t seed = 0)
  51   {
  52     val = seed;
  53     bits = 0;
  54   }
  55
  56   /* End incremential hashing and provide the final value.  */
  57   hashval_t end ()
  58   {
  59     return val;
  60   }
  61
  62   /* Add unsigned value V.  */
  63   void add_int (unsigned v)
  64   {
  65     val = iterative_hash_hashval_t (v, val);
  66   }
  67
  68   /* Add HOST_WIDE_INT value V.  */
  69   void add_wide_int (HOST_WIDE_INT v)
  70   {
  71     val = iterative_hash_host_wide_int (v, val);
  72   }
  73
  74   /* Hash in pointer PTR.  */
  75   void add_ptr (const void *ptr)
  76   {
  77     add (&ptr, sizeof (ptr));
  78   }
  79
  80   /* Add a memory block DATA with size LEN.  */
  81   void add (const void *data, size_t len)
  82   {
  83     val = iterative_hash (data, len, val);
  84   }
  85
  86   /* Merge hash value OTHER.  */
  87   void merge_hash (hashval_t other)
  88   {
  89     val = iterative_hash_hashval_t (other, val);
  90   }
  91
  92   /* Hash in state from other inchash OTHER.  */
  93   void merge (hash &other)
  94   {
  95     merge_hash (other.val);
  96   }
  97
  98   template<class T> void add_object(T &obj)
  99   {
 100     add (&obj, sizeof(T));
 101   }
 102
 103   /* Support for accumulating boolean flags */
 104
 105   void add_flag (bool flag)
 106   {
 107     bits = (bits << 1) | flag;
 108   }
 109
 110   void commit_flag ()
 111   {
 112     add_int (bits);
 113     bits = 0;
 114   }
 115
 116   /* Support for commutative hashing. Add A and B in a defined order
 117      based on their value. This is useful for hashing commutative
 118      expressions, so that A+B and B+A get the same hash.  */
 119
 120   void add_commutative (hash &a, hash &b)
 121   {
 122     if (a.end() > b.end())
 123       {
 124         merge (b);
 125         merge (a);
 126       }
 127     else
 128       {
 129         merge (a);
 130         merge (b);
 131       }
 132   }
 133
 134  private:
 135   hashval_t val;
 136   unsigned bits;
 137 };
 138
 139 }
 140
 141 /* Borrowed from hashtab.c iterative_hash implementation.  */
 142 #define mix(a,b,c) \
 143 { \
 144   a -= b; a -= c; a ^= (c>>13); \
 145   b -= c; b -= a; b ^= (a<< 8); \
 146   c -= a; c -= b; c ^= ((b&0xffffffff)>>13); \
 147   a -= b; a -= c; a ^= ((c&0xffffffff)>>12); \
 148   b -= c; b -= a; b = (b ^ (a<<16)) & 0xffffffff; \
 149   c -= a; c -= b; c = (c ^ (b>> 5)) & 0xffffffff; \
 150   a -= b; a -= c; a = (a ^ (c>> 3)) & 0xffffffff; \
 151   b -= c; b -= a; b = (b ^ (a<<10)) & 0xffffffff; \
 152   c -= a; c -= b; c = (c ^ (b>>15)) & 0xffffffff; \
 153 }
 154
 155
 156 /* Produce good hash value combining VAL and VAL2.  */
 157 inline
 158 hashval_t
 159 iterative_hash_hashval_t (hashval_t val, hashval_t val2)
 160 {
 161   /* the golden ratio; an arbitrary value.  */
 162   hashval_t a = 0x9e3779b9;
 163
 164   mix (a, val, val2);
 165   return val2;
 166 }
 167
 168 /* Produce good hash value combining VAL and VAL2.  */
 169
 170 inline
 171 hashval_t
 172 iterative_hash_host_wide_int (HOST_WIDE_INT val, hashval_t val2)
 173 {
 174   if (sizeof (HOST_WIDE_INT) == sizeof (hashval_t))
 175     return iterative_hash_hashval_t (val, val2);
 176   else
 177     {
 178       hashval_t a = (hashval_t) val;
 179       /* Avoid warnings about shifting of more than the width of the type on
 180          hosts that won't execute this path.  */
 181       int zero = 0;
 182       hashval_t b = (hashval_t) (val >> (sizeof (hashval_t) * 8 + zero));
 183       mix (a, b, val2);
 184       if (sizeof (HOST_WIDE_INT) > 2 * sizeof (hashval_t))
 185         {
 186           hashval_t a = (hashval_t) (val >> (sizeof (hashval_t) * 16 + zero));
 187           hashval_t b = (hashval_t) (val >> (sizeof (hashval_t) * 24 + zero));
 188           mix (a, b, val2);
 189         }
 190       return val2;
 191     }
 192 }
 193
 194 #endif