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/* An incremental hash abstract data type.
Copyright (C) 2014-2015 Free Software Foundation, Inc.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.
GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3. If not see
<http://www.gnu.org/licenses/>. */
#ifndef INCHASH_H
#define INCHASH_H 1
/* This file implements an incremential hash function ADT, to be used
by code that incrementially hashes a lot of unrelated data
(not in a single memory block) into a single value. The goal
is to make it easy to plug in efficient hash algorithms.
Currently it just implements the plain old jhash based
incremental hash from gcc's tree.c. */
hashval_t iterative_hash_host_wide_int (HOST_WIDE_INT, hashval_t);
hashval_t iterative_hash_hashval_t (hashval_t, hashval_t);
namespace inchash
{
class hash
{
public:
/* Start incremential hashing, optionally with SEED. */
hash (hashval_t seed = 0)
{
val = seed;
bits = 0;
}
/* End incremential hashing and provide the final value. */
hashval_t end ()
{
return val;
}
/* Add unsigned value V. */
void add_int (unsigned v)
{
val = iterative_hash_hashval_t (v, val);
}
/* Add HOST_WIDE_INT value V. */
void add_wide_int (HOST_WIDE_INT v)
{
val = iterative_hash_host_wide_int (v, val);
}
/* Hash in pointer PTR. */
void add_ptr (const void *ptr)
{
add (&ptr, sizeof (ptr));
}
/* Add a memory block DATA with size LEN. */
void add (const void *data, size_t len)
{
val = iterative_hash (data, len, val);
}
/* Merge hash value OTHER. */
void merge_hash (hashval_t other)
{
val = iterative_hash_hashval_t (other, val);
}
/* Hash in state from other inchash OTHER. */
void merge (hash &other)
{
merge_hash (other.val);
}
template<class T> void add_object(T &obj)
{
add (&obj, sizeof(T));
}
/* Support for accumulating boolean flags */
void add_flag (bool flag)
{
bits = (bits << 1) | flag;
}
void commit_flag ()
{
add_int (bits);
bits = 0;
}
/* Support for commutative hashing. Add A and B in a defined order
based on their value. This is useful for hashing commutative
expressions, so that A+B and B+A get the same hash. */
void add_commutative (hash &a, hash &b)
{
if (a.end() > b.end())
{
merge (b);
merge (a);
}
else
{
merge (a);
merge (b);
}
}
private:
hashval_t val;
unsigned bits;
};
}
/* Borrowed from hashtab.c iterative_hash implementation. */
#define mix(a,b,c) \
{ \
a -= b; a -= c; a ^= (c>>13); \
b -= c; b -= a; b ^= (a<< 8); \
c -= a; c -= b; c ^= ((b&0xffffffff)>>13); \
a -= b; a -= c; a ^= ((c&0xffffffff)>>12); \
b -= c; b -= a; b = (b ^ (a<<16)) & 0xffffffff; \
c -= a; c -= b; c = (c ^ (b>> 5)) & 0xffffffff; \
a -= b; a -= c; a = (a ^ (c>> 3)) & 0xffffffff; \
b -= c; b -= a; b = (b ^ (a<<10)) & 0xffffffff; \
c -= a; c -= b; c = (c ^ (b>>15)) & 0xffffffff; \
}
/* Produce good hash value combining VAL and VAL2. */
inline
hashval_t
iterative_hash_hashval_t (hashval_t val, hashval_t val2)
{
/* the golden ratio; an arbitrary value. */
hashval_t a = 0x9e3779b9;
mix (a, val, val2);
return val2;
}
/* Produce good hash value combining VAL and VAL2. */
inline
hashval_t
iterative_hash_host_wide_int (HOST_WIDE_INT val, hashval_t val2)
{
if (sizeof (HOST_WIDE_INT) == sizeof (hashval_t))
return iterative_hash_hashval_t (val, val2);
else
{
hashval_t a = (hashval_t) val;
/* Avoid warnings about shifting of more than the width of the type on
hosts that won't execute this path. */
int zero = 0;
hashval_t b = (hashval_t) (val >> (sizeof (hashval_t) * 8 + zero));
mix (a, b, val2);
if (sizeof (HOST_WIDE_INT) > 2 * sizeof (hashval_t))
{
hashval_t a = (hashval_t) (val >> (sizeof (hashval_t) * 16 + zero));
hashval_t b = (hashval_t) (val >> (sizeof (hashval_t) * 24 + zero));
mix (a, b, val2);
}
return val2;
}
}
#endif
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