Jonathon Fletcher
Basic gzip/gunzip in memory buffer examples using zlib code.
There are small changes needed to the zconf.h file in the zlib distribution (I used 1.2.7). The zlib license applies to the zlib code - I have only imported a subset of the source.
The MBED has limited memory, so we need the following (near the top of zconf.h) to restrict memory allocation sizes:
#define MAX_MEM_LEVEL 3 #define MAX_WBITS 10
Because MAX_MEM_LEVEL and MAX_WBITS are so much lower than the default, there is a danger that the mbed cannot gunzip data compressed by a 'normal' zlib build. My use-case is to gzip on the mbed more than gunzip on the mbed so I have not given much time to this issue.
I also included this (also near the top of zconf.h) to prefix defines with Z_
#define Z_PREFIX
In zconf.h, in the zlib distribution, the includes for <fcntl.h> and <sys/types.h> need commenting out when using the online compiler. No need when using GCC4MBED.
I also looked at miniz. I chose zlib because I needed the gzip headers and miniz does not implement them.
The sample main.cpp reads source data, compresses it, decompresses it, and finally compares the input data with the output data to confirm they are the same.
unsigned char input_data[2048];
unsigned long input_data_length = 0;
FILE *ifp = fopen("/local/src.txt", "r");
if (ifp) {
int br = fread(input_data, 1, sizeof(input_data), ifp);
fclose(ifp);
input_data_length = br;
}
printf("%s:%d: input_data_length:%lu%s", __FILE__, __LINE__, input_data_length, newline);
unsigned char gzip_data[2048];
unsigned long gzip_data_length = 0;
if (input_data_length > 0) {
gzip_data_length = sizeof(gzip_data);
int rv = gzip(gzip_data, &gzip_data_length, input_data, input_data_length);
if (Z_OK == rv) {
FILE *ofp = fopen("/local/dst.gz", "w");
if (ofp) {
int bw = fwrite(gzip_data, 1, gzip_data_length, ofp);
fclose(ofp);
}
} else {
printf("%s:%d: %d%s", __FILE__, __LINE__, rv, newline);
}
}
printf("%s:%d: gzip_data_length:%lu%s", __FILE__, __LINE__, gzip_data_length, newline);
unsigned char output_data[2048];
unsigned long output_data_length = 0;
if (gzip_data_length > 0) {
output_data_length = sizeof(output_data);
int rv = gunzip(output_data, &output_data_length, gzip_data, gzip_data_length);
if (Z_OK != rv) {
printf("%s:%d: %d%s", __FILE__, __LINE__, rv, newline);
}
}
printf("%s:%d: output_data_length:%lu%s", __FILE__, __LINE__, output_data_length, newline);
if (input_data_length > 0 and input_data_length > 0) {
bool input_matches_output = false;
if (input_data_length == output_data_length) {
input_matches_output = true;
for ( size_t i = 0 ; input_matches_output && i < input_data_length ; i++ ) {
if (input_data[i] != output_data[i]) {
input_matches_output = false;
}
}
}
printf("%s:%d: input (%lu bytes) %s output (%lu bytes)%s", __FILE__, __LINE__, input_data_length, input_matches_output?"matches":"does not match", output_data_length, newline);
} else {
printf("%s:%d: input and/or output length is 0%s", __FILE__, __LINE__, newline);
}
Diff: zlib/inftrees.h
- Revision:
- 0:54f5be781526
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/zlib/inftrees.h Sun Oct 21 07:46:41 2012 +0000
@@ -0,0 +1,62 @@
+/* inftrees.h -- header to use inftrees.c
+ * Copyright (C) 1995-2005, 2010 Mark Adler
+ * For conditions of distribution and use, see copyright notice in zlib.h
+ */
+
+/* WARNING: this file should *not* be used by applications. It is
+ part of the implementation of the compression library and is
+ subject to change. Applications should only use zlib.h.
+ */
+
+/* Structure for decoding tables. Each entry provides either the
+ information needed to do the operation requested by the code that
+ indexed that table entry, or it provides a pointer to another
+ table that indexes more bits of the code. op indicates whether
+ the entry is a pointer to another table, a literal, a length or
+ distance, an end-of-block, or an invalid code. For a table
+ pointer, the low four bits of op is the number of index bits of
+ that table. For a length or distance, the low four bits of op
+ is the number of extra bits to get after the code. bits is
+ the number of bits in this code or part of the code to drop off
+ of the bit buffer. val is the actual byte to output in the case
+ of a literal, the base length or distance, or the offset from
+ the current table to the next table. Each entry is four bytes. */
+typedef struct {
+ unsigned char op; /* operation, extra bits, table bits */
+ unsigned char bits; /* bits in this part of the code */
+ unsigned short val; /* offset in table or code value */
+} code;
+
+/* op values as set by inflate_table():
+ 00000000 - literal
+ 0000tttt - table link, tttt != 0 is the number of table index bits
+ 0001eeee - length or distance, eeee is the number of extra bits
+ 01100000 - end of block
+ 01000000 - invalid code
+ */
+
+/* Maximum size of the dynamic table. The maximum number of code structures is
+ 1444, which is the sum of 852 for literal/length codes and 592 for distance
+ codes. These values were found by exhaustive searches using the program
+ examples/enough.c found in the zlib distribtution. The arguments to that
+ program are the number of symbols, the initial root table size, and the
+ maximum bit length of a code. "enough 286 9 15" for literal/length codes
+ returns returns 852, and "enough 30 6 15" for distance codes returns 592.
+ The initial root table size (9 or 6) is found in the fifth argument of the
+ inflate_table() calls in inflate.c and infback.c. If the root table size is
+ changed, then these maximum sizes would be need to be recalculated and
+ updated. */
+#define ENOUGH_LENS 852
+#define ENOUGH_DISTS 592
+#define ENOUGH (ENOUGH_LENS+ENOUGH_DISTS)
+
+/* Type of code to build for inflate_table() */
+typedef enum {
+ CODES,
+ LENS,
+ DISTS
+} codetype;
+
+int ZLIB_INTERNAL inflate_table OF((codetype type, unsigned short FAR *lens,
+ unsigned codes, code FAR * FAR *table,
+ unsigned FAR *bits, unsigned short FAR *work));