gcc/inchash.h

   1 /* An incremental hash abstract data type.
   2    Copyright (C) 2014-2022 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.cc.  */
  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 polynomial value V, treating each element as an unsigned int.  */
  61   template<unsigned int N, typename T>
  62   void add_poly_int (const poly_int_pod<N, T> &v)
  63   {
  64     for (unsigned int i = 0; i < N; ++i)
  65       add_int (v.coeffs[i]);
  66   }
  67
  68   /* Add HOST_WIDE_INT value V.  */
  69   void add_hwi (HOST_WIDE_INT v)
  70   {
  71     val = iterative_hash_host_wide_int (v, val);
  72   }
  73
  74   /* Add polynomial value V, treating each element as a HOST_WIDE_INT.  */
  75   template<unsigned int N, typename T>
  76   void add_poly_hwi (const poly_int_pod<N, T> &v)
  77   {
  78     for (unsigned int i = 0; i < N; ++i)
  79       add_hwi (v.coeffs[i]);
  80   }
  81
  82   /* Add wide_int-based value V.  */
  83   template<typename T>
  84   void add_wide_int (const generic_wide_int<T> &x)
  85   {
  86     add_int (x.get_len ());
  87     for (unsigned i = 0; i < x.get_len (); i++)
  88       add_hwi (x.sext_elt (i));
  89   }
  90
  91   /* Hash in pointer PTR.  */
  92   void add_ptr (const void *ptr)
  93   {
  94     add (&ptr, sizeof (ptr));
  95   }
  96
  97   /* Add a memory block DATA with size LEN.  */
  98   void add (const void *data, size_t len)
  99   {
 100     val = iterative_hash (data, len, val);
 101   }
 102
 103   /* Merge hash value OTHER.  */
 104   void merge_hash (hashval_t other)
 105   {
 106     val = iterative_hash_hashval_t (other, val);
 107   }
 108
 109   /* Hash in state from other inchash OTHER.  */
 110   void merge (hash &other)
 111   {
 112     merge_hash (other.val);
 113   }
 114
 115   template<class T> void add_object(T &obj)
 116   {
 117     add (&obj, sizeof(T));
 118   }
 119
 120   /* Support for accumulating boolean flags */
 121
 122   void add_flag (bool flag)
 123   {
 124     bits = (bits << 1) | flag;
 125   }
 126
 127   void commit_flag ()
 128   {
 129     add_int (bits);
 130     bits = 0;
 131   }
 132
 133   /* Support for commutative hashing. Add A and B in a defined order
 134      based on their value. This is useful for hashing commutative
 135      expressions, so that A+B and B+A get the same hash.  */
 136
 137   void add_commutative (hash &a, hash &b)
 138   {
 139     if (a.end() > b.end())
 140       {
 141         merge (b);
 142         merge (a);
 143       }
 144     else
 145       {
 146         merge (a);
 147         merge (b);
 148       }
 149   }
 150
 151  private:
 152   hashval_t val;
 153   unsigned bits;
 154 };
 155
 156 }
 157
 158 /* Borrowed from hashtab.c iterative_hash implementation.  */
 159 #define mix(a,b,c) \
 160 { \
 161   a -= b; a -= c; a ^= (c>>13); \
 162   b -= c; b -= a; b ^= (a<< 8); \
 163   c -= a; c -= b; c ^= ((b&0xffffffff)>>13); \
 164   a -= b; a -= c; a ^= ((c&0xffffffff)>>12); \
 165   b -= c; b -= a; b = (b ^ (a<<16)) & 0xffffffff; \
 166   c -= a; c -= b; c = (c ^ (b>> 5)) & 0xffffffff; \
 167   a -= b; a -= c; a = (a ^ (c>> 3)) & 0xffffffff; \
 168   b -= c; b -= a; b = (b ^ (a<<10)) & 0xffffffff; \
 169   c -= a; c -= b; c = (c ^ (b>>15)) & 0xffffffff; \
 170 }
 171
 172
 173 /* Produce good hash value combining VAL and VAL2.  */
 174 inline
 175 hashval_t
 176 iterative_hash_hashval_t (hashval_t val, hashval_t val2)
 177 {
 178   /* the golden ratio; an arbitrary value.  */
 179   hashval_t a = 0x9e3779b9;
 180
 181   mix (a, val, val2);
 182   return val2;
 183 }
 184
 185 /* Produce good hash value combining VAL and VAL2.  */
 186
 187 inline
 188 hashval_t
 189 iterative_hash_host_wide_int (HOST_WIDE_INT val, hashval_t val2)
 190 {
 191   if (sizeof (HOST_WIDE_INT) == sizeof (hashval_t))
 192     return iterative_hash_hashval_t (val, val2);
 193   else
 194     {
 195       hashval_t a = (hashval_t) val;
 196       /* Avoid warnings about shifting of more than the width of the type on
 197          hosts that won't execute this path.  */
 198       int zero = 0;
 199       hashval_t b = (hashval_t) (val >> (sizeof (hashval_t) * 8 + zero));
 200       mix (a, b, val2);
 201       if (sizeof (HOST_WIDE_INT) > 2 * sizeof (hashval_t))
 202         {
 203           hashval_t a = (hashval_t) (val >> (sizeof (hashval_t) * 16 + zero));
 204           hashval_t b = (hashval_t) (val >> (sizeof (hashval_t) * 24 + zero));
 205           mix (a, b, val2);
 206         }
 207       return val2;
 208     }
 209 }
 210
 211 #endif