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/**
* @file llpredicate.h
* @brief abstraction for filtering objects by predicates, with arbitrary boolean expressions
*
* $LicenseInfo:firstyear=2008&license=viewerlgpl$
* Second Life Viewer Source Code
* Copyright (C) 2010, Linden Research, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation;
* version 2.1 of the License only.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*
* Linden Research, Inc., 945 Battery Street, San Francisco, CA 94111 USA
* $/LicenseInfo$
*/
#ifndef LL_LLPREDICATE_H
#define LL_LLPREDICATE_H
#include "llerror.h"
namespace LLPredicate
{
template<typename ENUM> class Rule;
extern const U32 cPredicateFlagsFromEnum[5];
template<typename ENUM>
class Literal
{
friend Rule<ENUM>;
public:
typedef U32 predicate_flag_t;
static const S32 cMaxEnum = 5;
Literal(ENUM e)
: mPredicateFlags(cPredicateFlagsFromEnum[e])
{
llassert(0 <= e && e < cMaxEnum);
}
Literal()
: mPredicateFlags(0xFFFFffff)
{}
Literal operator~()
{
Literal new_rule;
new_rule.mPredicateFlags = ~mPredicateFlags;
return new_rule;
}
Literal operator &&(const Literal& other)
{
Literal new_rule;
new_rule.mPredicateFlags = mPredicateFlags & other.mPredicateFlags;
return new_rule;
}
Literal operator ||(const Literal& other)
{
Literal new_rule;
new_rule.mPredicateFlags = mPredicateFlags | other.mPredicateFlags;
return new_rule;
}
void set(ENUM e, bool value)
{
llassert(0 <= e && e < cMaxEnum);
modifyPredicate(0x1 << (S32)e, cPredicateFlagsFromEnum[e], value);
}
void set(const Literal& other, bool value)
{
U32 predicate_flags = other.mPredicateFlags;
while(predicate_flags)
{
U32 next_flags = clearLSB(predicate_flags);
lsb_flag = predicate_flags ^ next_flags;
U32 mask = 0;
for (S32 i = 0; i < cMaxEnum; i++)
{
if (cPredicateFlagsFromEnum[i] & lsb_flag)
{
mask |= cPredicateFlagsFromEnum[i];
}
}
modifyPredicate(lsb_flag, mask, value);
predicate_flags = next_flags;
}
}
void forget(ENUM e)
{
set(e, true);
U32 flags_with_predicate = mPredicateFlags;
set(e, false);
// ambiguous value is result of adding and removing predicate at the same time!
mPredicateFlags |= flags_with_predicate;
}
void forget(const Literal& literal)
{
set(literal, true);
U32 flags_with_predicate = mPredicateFlags;
set(literal, false);
// ambiguous value is result of adding and removing predicate at the same time!
mPredicateFlags |= flags_with_predicate;
}
private:
predicate_flag_t clearLSB(predicate_flag_t value)
{
return value & (value - 1);
}
void modifyPredicate(predicate_flag_t predicate_flag, predicate_flag_t mask, bool value)
{
llassert(clearLSB(predicate_flag) == 0);
predicate_flag_t flags_to_modify;
if (value)
{
flags_to_modify = (mPredicateFlags & ~mask);
// clear flags not containing predicate to be added
mPredicateFlags &= mask;
// shift flags, in effect adding predicate
flags_to_modify *= predicate_flag;
}
else
{
flags_to_modify = mPredicateFlags & mask;
// clear flags containing predicate to be removed
mPredicateFlags &= ~mask;
// shift flags, in effect removing predicate
flags_to_modify /= predicate_flag;
}
// put modified flags back
mPredicateFlags |= flags_to_modify;
}
predicate_flag_t mPredicateFlags;
};
template<typename ENUM>
struct Value
: public Literal<ENUM>
{
public:
Value(ENUM e)
: Literal(e)
{}
Value()
{}
};
template<typename ENUM>
class Rule
: public Literal<ENUM>
{
public:
Rule(ENUM value)
: Literal(value)
{}
Rule(const Literal other)
: Literal(other)
{}
Rule()
{}
bool check(const Value<ENUM>& value) const
{
return (value.mPredicateFlags & mPredicateFlags) != 0;
}
bool isTriviallyTrue() const
{
return mPredicateFlags == 0xFFFFffff;
}
bool isTriviallyFalse() const
{
return mPredicateFlags == 0;
}
};
}
template<typename ENUM>
LLPredicate::Literal<ENUM> ll_predicate(ENUM e)
{
return LLPredicate::Literal<ENUM>(e);
}
#endif // LL_LLPREDICATE_H
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