ZSTD_create?Dict() is required to produce a ?Dict* return type
because `free()` does not accept a `const type*` argument.
If it wasn't for this restriction, I would have preferred to create a `const ?Dict*` object
to emphasize the fact that, once created, a dictionary never changes
(hence can be shared concurrently until the end of its lifetime).
There is no such limitation with initStatic?Dict() :
as stated in the doc, there is no corresponding free() function,
since `workspace` is provided, hence allocated, externally,
it can only be free() externally.
Which means, ZSTD_initStatic?Dict() can return a `const ZSTD_?Dict*` pointer.
Tested with `make all`, to catch initStatic's users,
which, incidentally, also updated zstd.h documentation.
it was invoking ZSTD_initCStream_advanced() with pledgedSrcSize==0 and contentSizeFlag=1
which means "empty"
while the intention was to mean "unknown".
The contentSizeFlag==1 is new, it is a consequence of setting this value to 1 by default.
The solution selected here is to pass ZSTD_CONTENTSIZE_UNKNOWN to mean "unknown".
So contentSizeFlag remains set (it wasn't in previous versions).
to mean "pledgedSrcSize is not known at init time" instead of `0`.
Note that, a few prototypes created and documented with `0` to mean "unknown" still interpret "0" as unknown,
to avoid breaking 3rd party applications which depend on this behavior.
But this value is no longer recommended to mean "unknown".
In some future version, it might be possible to switch "0" to mean "empty",
as is already the case for several prototypes.
The advantage is that pledgedSrcSize field would have same behavior accross entire API,
making it easier to reason about.
Note that all concerned prototypes belong to the "experimental" API section.
srcSize is controlled at end of compression,
so if someone uses "0" to mean "unknown" while it effectively means "empty",
this is immediately caught by the compression function, which generates an error code : ZSTD_ERROR_srcSize_wrong
supporting function for bufferless streaming API (ZSTD_decompressContinue())
makes it possible to correctly size a round buffer for decoding using this API.
also : added field blockSizeMax within ZSTD_frameHeader,
as it's a necessary information to know when to restart at beginning of decoding buffer.
Makes frame type (zstd,skippable) detection more straighforward.
ZSTD_getFrameHeader set frameContentSize=ZSTD_CONTENTSIZE_UNKNOWN to mean "field not present"
use less macro statements
the initial version was meant to work with STATIC_ASSERT
but since it doesn't work and needs assert()
it's possible to rewrite it using normally compiled code
which is better for compiler.
Downside : the error message is less precise.
There is a DEBUGLOG(3,) to compensate.
ZSTD_estimateCDictSize() now uses same arguments as ZSTD_createCDict()
ZSTD_estimateCDictSize_advanced() uses same arguments as ZSTD_createCDict_advanced()
ZSTD_estimateCCtx() is now a "simple" function,
taking int compressionLevel as single argument.
ZSTD_estimateCCtx_advanced() takes a CParams argument,
which is both more complete and more complex to generate.
Doesn't speed optimize this buffer-to-buffer scenario yet.
Still internally defers to streaming implementation.
Also : fixed a long standing bug in ZSTDMT streaming API.
