Chris@43: Puff -- A Simple Inflate
Chris@43: 3 Mar 2003
Chris@43: Mark Adler
Chris@43: madler@alumni.caltech.edu
Chris@43: 
Chris@43: What this is --
Chris@43: 
Chris@43: puff.c provides the routine puff() to decompress the deflate data format.  It
Chris@43: does so more slowly than zlib, but the code is about one-fifth the size of the
Chris@43: inflate code in zlib, and written to be very easy to read.
Chris@43: 
Chris@43: Why I wrote this --
Chris@43: 
Chris@43: puff.c was written to document the deflate format unambiguously, by virtue of
Chris@43: being working C code.  It is meant to supplement RFC 1951, which formally
Chris@43: describes the deflate format.  I have received many questions on details of the
Chris@43: deflate format, and I hope that reading this code will answer those questions.
Chris@43: puff.c is heavily commented with details of the deflate format, especially
Chris@43: those little nooks and cranies of the format that might not be obvious from a
Chris@43: specification.
Chris@43: 
Chris@43: puff.c may also be useful in applications where code size or memory usage is a
Chris@43: very limited resource, and speed is not as important.
Chris@43: 
Chris@43: How to use it --
Chris@43: 
Chris@43: Well, most likely you should just be reading puff.c and using zlib for actual
Chris@43: applications, but if you must ...
Chris@43: 
Chris@43: Include puff.h in your code, which provides this prototype:
Chris@43: 
Chris@43: int puff(unsigned char *dest,           /* pointer to destination pointer */
Chris@43:          unsigned long *destlen,        /* amount of output space */
Chris@43:          unsigned char *source,         /* pointer to source data pointer */
Chris@43:          unsigned long *sourcelen);     /* amount of input available */
Chris@43: 
Chris@43: Then you can call puff() to decompress a deflate stream that is in memory in
Chris@43: its entirety at source, to a sufficiently sized block of memory for the
Chris@43: decompressed data at dest.  puff() is the only external symbol in puff.c  The
Chris@43: only C library functions that puff.c needs are setjmp() and longjmp(), which
Chris@43: are used to simplify error checking in the code to improve readabilty.  puff.c
Chris@43: does no memory allocation, and uses less than 2K bytes off of the stack.
Chris@43: 
Chris@43: If destlen is not enough space for the uncompressed data, then inflate will
Chris@43: return an error without writing more than destlen bytes.  Note that this means
Chris@43: that in order to decompress the deflate data successfully, you need to know
Chris@43: the size of the uncompressed data ahead of time.
Chris@43: 
Chris@43: If needed, puff() can determine the size of the uncompressed data with no
Chris@43: output space.  This is done by passing dest equal to (unsigned char *)0.  Then
Chris@43: the initial value of *destlen is ignored and *destlen is set to the length of
Chris@43: the uncompressed data.  So if the size of the uncompressed data is not known,
Chris@43: then two passes of puff() can be used--first to determine the size, and second
Chris@43: to do the actual inflation after allocating the appropriate memory.  Not
Chris@43: pretty, but it works.  (This is one of the reasons you should be using zlib.)
Chris@43: 
Chris@43: The deflate format is self-terminating.  If the deflate stream does not end
Chris@43: in *sourcelen bytes, puff() will return an error without reading at or past
Chris@43: endsource.
Chris@43: 
Chris@43: On return, *sourcelen is updated to the amount of input data consumed, and
Chris@43: *destlen is updated to the size of the uncompressed data.  See the comments
Chris@43: in puff.c for the possible return codes for puff().