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Diffstat (limited to 'src/include/util')
| -rw-r--r-- | src/include/util/memoize.H | 108 |
1 files changed, 108 insertions, 0 deletions
diff --git a/src/include/util/memoize.H b/src/include/util/memoize.H new file mode 100644 index 000000000..e1f31c48c --- /dev/null +++ b/src/include/util/memoize.H @@ -0,0 +1,108 @@ +/* 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 |
