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