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| 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(). | ||