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/* IBM_PROLOG_BEGIN_TAG */
/* This is an automatically generated prolog. */
/* */
/* $Source: src/include/util/memoize.H $ */
/* */
/* OpenPOWER HostBoot Project */
/* */
/* Contributors Listed Below - COPYRIGHT 2016 */
/* [+] International Business Machines Corp. */
/* */
/* */
/* Licensed under the Apache License, Version 2.0 (the "License"); */
/* you may not use this file except in compliance with the License. */
/* You may obtain a copy of the License at */
/* */
/* http://www.apache.org/licenses/LICENSE-2.0 */
/* */
/* Unless required by applicable law or agreed to in writing, software */
/* distributed under the License is distributed on an "AS IS" BASIS, */
/* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or */
/* implied. See the License for the specific language governing */
/* permissions and limitations under the License. */
/* */
/* IBM_PROLOG_END_TAG */
#ifndef __UTIL_MEMOIZE_H
#define __UTIL_MEMOIZE_H
#include <errl/errlentry.H>
#include <map>
namespace Util
{
namespace Memoize
{
/**
* @brief Wraps a function (which accepts an input/output parameter pair and
* returns an error log handle) with a memoizer
*
* @par Detailed Description:
* This template wraps a candidate function with a memoizer, a facility
* which caches the result for every unique input. If an input arrives
* that already has a cached result, the result is returned without the
* overhead of calling the function, thereby increasing performance.
* See warning section for caveats.
*
* @warning: Must only be used if:
* - Called only in single-threaded context (cache is not mutex protected)
* - All possible inputs are guaranteed to be unique
* - For a given input, the result is always the same
*
* @tparam InputType The memoized function's input type
* @tparam OutputType The memoized function's output type
* @param[in] i_fn Function pointer referencing the function to memoize
* @param[in] i_in Input to the memoized function
* @param[out] o_out Output of the memoized function. The memoizer does not
* alter the output on failure; Caller should default the value as
* appropriate to anticipate that case.
* @return Error log indicating success or failure
* @retval NULL Result was already computed for the given input and was
* returned in the output parameter -otherwise- real function returned
* a value that was cached and returned in the output parameter
* @retval !NULL Call to memoized function failed. Result was not cached and
* the output value remains unchanged
* @note: Could be improved to return a lambda function and use
* std::function in place of function pointers if std::function was
* implemented
*/
template < class InputType , class OutputType >
errlHndl_t memoize(
errlHndl_t (*i_fn)(InputType,OutputType&),
InputType i_in,
OutputType& o_out)
{
errlHndl_t pError = NULL;
do {
// If the result of the input is already cached, return it
static std::map< InputType, OutputType> cache;
if(cache.count(i_in))
{
o_out = cache[i_in];
break;
}
// Otherwise call the real function and assuming no error, cache the result
// and return it
OutputType out;
pError = i_fn(i_in,out);
if(!pError)
{
cache[i_in] = out;
o_out = out;
}
} while(0);
return pError;
}
}; // End namespace Memoize
}; // End namespace Util
#endif
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