gcc/inchash.h

   1 /* An incremental hash abstract data type.
   2    Copyright (C) 2014-2024 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<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<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   void add_real_value (const class real_value &v);
  92
  93   /* Hash in pointer PTR.  */
  94   void add_ptr (const void *ptr)
  95   {
  96     add (&ptr, sizeof (ptr));
  97   }
  98
  99   /* Add a memory block DATA with size LEN.  */
 100   void add (const void *data, size_t len)
 101   {
 102     val = iterative_hash (data, len, val);
 103   }
 104
 105   /* Merge hash value OTHER.  */
 106   void merge_hash (hashval_t other)
 107   {
 108     val = iterative_hash_hashval_t (other, val);
 109   }
 110
 111   /* Hash in state from other inchash OTHER.  */
 112   void merge (hash &other)
 113   {
 114     merge_hash (other.val);
 115   }
 116
 117   template<class T> void add_object(T &obj)
 118   {
 119     add (&obj, sizeof(T));
 120   }
 121
 122   /* Support for accumulating boolean flags */
 123
 124   void add_flag (bool flag)
 125   {
 126     bits = (bits << 1) | flag;
 127   }
 128
 129   void commit_flag ()
 130   {
 131     add_int (bits);
 132     bits = 0;
 133   }
 134
 135   /* Support for commutative hashing. Add A and B in a defined order
 136      based on their value. This is useful for hashing commutative
 137      expressions, so that A+B and B+A get the same hash.  */
 138
 139   void add_commutative (hash &a, hash &b)
 140   {
 141     if (a.end() > b.end())
 142       {
 143         merge (b);
 144         merge (a);
 145       }
 146     else
 147       {
 148         merge (a);
 149         merge (b);
 150       }
 151   }
 152
 153  private:
 154   hashval_t val;
 155   unsigned bits;
 156 };
 157
 158 }
 159
 160 /* Borrowed from hashtab.c iterative_hash implementation.  */
 161 #define mix(a,b,c) \
 162 { \
 163   a -= b; a -= c; a ^= (c>>13); \
 164   b -= c; b -= a; b ^= (a<< 8); \
 165   c -= a; c -= b; c ^= ((b&0xffffffff)>>13); \
 166   a -= b; a -= c; a ^= ((c&0xffffffff)>>12); \
 167   b -= c; b -= a; b = (b ^ (a<<16)) & 0xffffffff; \
 168   c -= a; c -= b; c = (c ^ (b>> 5)) & 0xffffffff; \
 169   a -= b; a -= c; a = (a ^ (c>> 3)) & 0xffffffff; \
 170   b -= c; b -= a; b = (b ^ (a<<10)) & 0xffffffff; \
 171   c -= a; c -= b; c = (c ^ (b>>15)) & 0xffffffff; \
 172 }
 173
 174
 175 /* Produce good hash value combining VAL and VAL2.  */
 176 inline
 177 hashval_t
 178 iterative_hash_hashval_t (hashval_t val, hashval_t val2)
 179 {
 180   /* the golden ratio; an arbitrary value.  */
 181   hashval_t a = 0x9e3779b9;
 182
 183   mix (a, val, val2);
 184   return val2;
 185 }
 186
 187 /* Produce good hash value combining VAL and VAL2.  */
 188
 189 inline
 190 hashval_t
 191 iterative_hash_host_wide_int (HOST_WIDE_INT val, hashval_t val2)
 192 {
 193   if (sizeof (HOST_WIDE_INT) == sizeof (hashval_t))
 194     return iterative_hash_hashval_t (val, val2);
 195   else
 196     {
 197       hashval_t a = (hashval_t) val;
 198       /* Avoid warnings about shifting of more than the width of the type on
 199          hosts that won't execute this path.  */
 200       int zero = 0;
 201       hashval_t b = (hashval_t) (val >> (sizeof (hashval_t) * 8 + zero));
 202       mix (a, b, val2);
 203       if (sizeof (HOST_WIDE_INT) > 2 * sizeof (hashval_t))
 204         {
 205           hashval_t a = (hashval_t) (val >> (sizeof (hashval_t) * 16 + zero));
 206           hashval_t b = (hashval_t) (val >> (sizeof (hashval_t) * 24 + zero));
 207           mix (a, b, val2);
 208         }
 209       return val2;
 210     }
 211 }
 212
 213 #endif