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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 madler@alumni.caltech.edu
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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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