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Add comment about not using windowBits of 8 for deflate().

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Mark Adler 2015-07-28 21:06:06 -07:00
parent e7ebb399d7
commit b56d1c62ee
1 changed files with 8 additions and 0 deletions
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zlib.h
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@ -544,6 +544,14 @@ ZEXTERN int ZEXPORT deflateInit2 OF((z_streamp strm,
compression at the expense of memory usage. The default value is 15 if
deflateInit is used instead.
For the current implementation of deflate(), a windowBits value of 8 (a
window size of 256 bytes) is not supported. As a result, a request for 8
will result in 9 (a 512-byte window). In that case, providing 8 to
inflateInit2() will result in an error when the zlib header with 9 is
checked against the initialization of inflate(). The remedy is to not use 8
with deflateInit2() with this initialization, or at least in that case use 9
with inflateInit2().
windowBits can also be -8..-15 for raw deflate. In this case, -windowBits
determines the window size. deflate() will then generate raw deflate data
with no zlib header or trailer, and will not compute an adler32 check value.