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Commit | Line | Data |
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7c673cae FG |
1 | Puff -- A Simple Inflate |
2 | 3 Mar 2003 | |
3 | Mark Adler | |
4 | madler@alumni.caltech.edu | |
5 | ||
6 | What this is -- | |
7 | ||
8 | puff.c provides the routine puff() to decompress the deflate data format. It | |
9 | does so more slowly than zlib, but the code is about one-fifth the size of the | |
10 | inflate code in zlib, and written to be very easy to read. | |
11 | ||
12 | Why I wrote this -- | |
13 | ||
14 | puff.c was written to document the deflate format unambiguously, by virtue of | |
15 | being working C code. It is meant to supplement RFC 1951, which formally | |
16 | describes the deflate format. I have received many questions on details of the | |
17 | deflate format, and I hope that reading this code will answer those questions. | |
18 | puff.c is heavily commented with details of the deflate format, especially | |
19 | those little nooks and cranies of the format that might not be obvious from a | |
20 | specification. | |
21 | ||
22 | puff.c may also be useful in applications where code size or memory usage is a | |
23 | very limited resource, and speed is not as important. | |
24 | ||
25 | How to use it -- | |
26 | ||
27 | Well, most likely you should just be reading puff.c and using zlib for actual | |
28 | applications, but if you must ... | |
29 | ||
30 | Include puff.h in your code, which provides this prototype: | |
31 | ||
32 | int puff(unsigned char *dest, /* pointer to destination pointer */ | |
33 | unsigned long *destlen, /* amount of output space */ | |
34 | unsigned char *source, /* pointer to source data pointer */ | |
35 | unsigned long *sourcelen); /* amount of input available */ | |
36 | ||
37 | Then you can call puff() to decompress a deflate stream that is in memory in | |
38 | its entirety at source, to a sufficiently sized block of memory for the | |
39 | decompressed data at dest. puff() is the only external symbol in puff.c The | |
40 | only C library functions that puff.c needs are setjmp() and longjmp(), which | |
41 | are used to simplify error checking in the code to improve readabilty. puff.c | |
42 | does no memory allocation, and uses less than 2K bytes off of the stack. | |
43 | ||
44 | If destlen is not enough space for the uncompressed data, then inflate will | |
45 | return an error without writing more than destlen bytes. Note that this means | |
46 | that in order to decompress the deflate data successfully, you need to know | |
47 | the size of the uncompressed data ahead of time. | |
48 | ||
49 | If needed, puff() can determine the size of the uncompressed data with no | |
50 | output space. This is done by passing dest equal to (unsigned char *)0. Then | |
51 | the initial value of *destlen is ignored and *destlen is set to the length of | |
52 | the uncompressed data. So if the size of the uncompressed data is not known, | |
53 | then two passes of puff() can be used--first to determine the size, and second | |
54 | to do the actual inflation after allocating the appropriate memory. Not | |
55 | pretty, but it works. (This is one of the reasons you should be using zlib.) | |
56 | ||
57 | The deflate format is self-terminating. If the deflate stream does not end | |
58 | in *sourcelen bytes, puff() will return an error without reading at or past | |
59 | endsource. | |
60 | ||
61 | On return, *sourcelen is updated to the amount of input data consumed, and | |
62 | *destlen is updated to the size of the uncompressed data. See the comments | |
63 | in puff.c for the possible return codes for puff(). |