Function bound

pub fn bound(stream: Option<&mut DeflateStream<'_>>, source_len: usize) -> usize

For the default windowBits of 15 and memLevel of 8, this function returns a close to exact, as well as small, upper bound on the compressed size. They are coded as constants here for a reason–if the #define’s are changed, then this function needs to be changed as well. The return value for 15 and 8 only works for those exact settings.

For any setting other than those defaults for windowBits and memLevel, the value returned is a conservative worst case for the maximum expansion resulting from using fixed blocks instead of stored blocks, which deflate can emit on compressed data for some combinations of the parameters.

This function could be more sophisticated to provide closer upper bounds for every combination of windowBits and memLevel. But even the conservative upper bound of about 14% expansion does not seem onerous for output buffer allocation.