| 1 | Puff -- A Simple Inflate
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| 2 | 3 Mar 2003
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| 3 | Mark Adler
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| 4 | [email protected]
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| 5 |
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| 6 | What this is --
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| 7 |
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| 8 | puff.c provides the routine puff() to decompress the deflate data format. It
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| 9 | does so more slowly than zlib, but the code is about one-fifth the size of the
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| 10 | inflate code in zlib, and written to be very easy to read.
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| 11 |
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| 12 | Why I wrote this --
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| 13 |
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| 14 | puff.c was written to document the deflate format unambiguously, by virtue of
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| 15 | being working C code. It is meant to supplement RFC 1951, which formally
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| 16 | describes the deflate format. I have received many questions on details of the
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| 17 | deflate format, and I hope that reading this code will answer those questions.
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| 18 | puff.c is heavily commented with details of the deflate format, especially
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| 19 | those little nooks and cranies of the format that might not be obvious from a
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| 20 | specification.
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| 21 |
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| 22 | puff.c may also be useful in applications where code size or memory usage is a
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| 23 | very limited resource, and speed is not as important.
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| 24 |
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| 25 | How to use it --
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| 26 |
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| 27 | Well, most likely you should just be reading puff.c and using zlib for actual
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| 28 | applications, but if you must ...
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| 29 |
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| 30 | Include puff.h in your code, which provides this prototype:
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| 31 |
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| 32 | int puff(unsigned char *dest, /* pointer to destination pointer */
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| 33 | unsigned long *destlen, /* amount of output space */
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| 34 | unsigned char *source, /* pointer to source data pointer */
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| 35 | unsigned long *sourcelen); /* amount of input available */
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| 36 |
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| 37 | Then you can call puff() to decompress a deflate stream that is in memory in
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| 38 | its entirety at source, to a sufficiently sized block of memory for the
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| 39 | decompressed data at dest. puff() is the only external symbol in puff.c The
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| 40 | only C library functions that puff.c needs are setjmp() and longjmp(), which
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| 41 | are used to simplify error checking in the code to improve readabilty. puff.c
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| 42 | does no memory allocation, and uses less than 2K bytes off of the stack.
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| 43 |
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| 44 | If destlen is not enough space for the uncompressed data, then inflate will
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| 45 | return an error without writing more than destlen bytes. Note that this means
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| 46 | that in order to decompress the deflate data successfully, you need to know
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| 47 | the size of the uncompressed data ahead of time.
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| 48 |
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| 49 | If needed, puff() can determine the size of the uncompressed data with no
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| 50 | output space. This is done by passing dest equal to (unsigned char *)0. Then
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| 51 | the initial value of *destlen is ignored and *destlen is set to the length of
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| 52 | the uncompressed data. So if the size of the uncompressed data is not known,
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| 53 | then two passes of puff() can be used--first to determine the size, and second
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| 54 | to do the actual inflation after allocating the appropriate memory. Not
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| 55 | pretty, but it works. (This is one of the reasons you should be using zlib.)
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| 56 |
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| 57 | The deflate format is self-terminating. If the deflate stream does not end
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| 58 | in *sourcelen bytes, puff() will return an error without reading at or past
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| 59 | endsource.
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| 60 |
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| 61 | On return, *sourcelen is updated to the amount of input data consumed, and
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| 62 | *destlen is updated to the size of the uncompressed data. See the comments
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| 63 | in puff.c for the possible return codes for puff().
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