The nbSeq "short" format (1-byte)
is compatible with any value < 128.
However, the code would cautiously only accept values < 127.
This is not an error, because the general 2-bytes format
is compatible with small values < 128.
Hence the inefficiency never triggered any warning.
Spotted by Intel's Smita Kumar.
When we wrote one byte beyond the end of the buffer for RLE
blocks back in 1.3.7, we would then have `op > oend`. That is
a problem when we use `oend - op` for the size of the destination
buffer, and allows further writes beyond the end of the buffer for
the rest of the function. Lets assert that it doesn't happen.
Also : minor speed optimization :
shortcut to ZSTD_reset_matchState() rather than the full reset process.
It still needs to be completed with ZSTD_continueCCtx() for proper initialization.
Also : changed position of LDM hash tables in the context,
so that the "regular" hash tables can be at a predictable position,
hence allowing the shortcut to ZSTD_reset_matchState() without complex conditions.
* Extract the overflow correction into a helper function.
* Load the dictionary `ZSTD_CHUNKSIZE_MAX = 512 MB` bytes at a time
and overflow correct between each chunk.
Data corruption could happen when all these conditions are true:
* You are using multithreading mode
* Your overlap size is >= 512 MB (implies window size >= 512 MB)
* You are using a strategy >= ZSTD_btlazy
* You are compressing more than 4 GB
The problem is that when loading a large dictionary we don't do
overflow correction. We can only load 512 MB at a time, and may
need to do overflow correction before each chunk.
