Memory usage of Reduce could be B larger than desired.

[SSoelvsten]

The memory consumption of the two external_sorters in adiar/internal/reduce.h does not take the size of the tpie::file_stream<mapping> red1_mapping into account.

• [x] Reverse engineer the size of a tpie::file_stream on a tpie::temp_file depending on the size of the struct and the block size. That is, do some experiments in src/main.cpp on the memory usage of the tpie::file_stream given some structs of different size and some different block sizes. To do this, check the available_memory before and after creating the tpie::file_stream.
  • [x] Add the results here in a comment.
  • [x] Add an inline function tpie_file_stream_memory_usage in internal/memory.h which are made accessible on the file_stream and file_writers as static functions memory_usage.
• [x] Subtract the memory usage of the one file stream from the available_memory given to __reduce_level.

[SSoelvsten]

@AnnaBlume99 Did some experiments on the tpie::file_stream<T> (not using tpie::temp_file) and figured out that the memory usage (after writing one or more elements) is 8 bytes + B

[SSoelvsten]

I forgot to branch before pushing.