[io] Add support for long range references in TBufferFile.cxx #21193
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pcanal
commented
Feb 8, 2026
pcanal
commented
Fixes root-project#14770 [io] add more checks in TBuffer functions as suggested by jblomer
In order to support 64 bits byte counts, which do not fit in the space reserved for them in the stream (4 bytes minus 2 control bits) and to work around the fact that the variables that holds the position and the byte count information in Streamer functions are only 32 bits (see arguments to TBufferFile::WriteVersion and TBufferFile::ReadVersion), we need to pass them indirectly when they needs 64 bits Since the streaming is inherently serial, we can leverage the sequence of calls and cache the 64 bits values in a queue. The bytecount that can not be stored in place inside the io stream will be held in a collection (fByteCounts) that need to be stored externally to the buffer.
Note to store and restore the larger than 1GB byte count use:
// Copy the content of the const reference.
auto bytecounts{b.GetByteCounts()};
...
b.SetByteCounts(std::move(bytecounts));
For now, the testing of the long range references is disabled.
References for class names and objects are stored in 64bits whenever they are located past 1GB. This is the 'only' option as there are no control bits left to distinguish between a 32bits and a 64bits reference.
Reference in the longRange section (>1GB) are now tagged so that we can differentiate nullptr (stored as only 32 bits) from short reference stored in the longRange section (i.e. those are stored in 64 bits but have only zeros in the high bit).
pcanal
requested review from
bellenot,
dpiparo,
hageboeck,
jblomer,
linev,
martamaja10 and
vepadulano
as code owners
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