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cc65/samples/gunzip65.c

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/*
* gunzip65 - a gunzip utility for 6502-based machines.
*
* Piotr Fusik <fox@scene.pl>
*
* This should be considered as a test of my zlib-compatible library
* rather than a real application.
* It's not user-friendly, fault-tolerant, whatever.
* However, it really works for real GZIP files, provided they are small
* enough to fit in buffer[] (after decompression!).
*/
#include <stdio.h>
#include <string.h>
#include <zlib.h>
#ifndef __CC65__
/*
* Emulate inflatemem() if using original zlib.
* As you can see, this program is quite portable.
*/
unsigned inflatemem(char* dest, const char* source)
{
z_stream stream;
stream.next_in = (Bytef*) source;
stream.avail_in = 65535;
stream.next_out = dest;
stream.avail_out = 65535;
stream.zalloc = (alloc_func) 0;
stream.zfree = (free_func) 0;
inflateInit2(&stream, -MAX_WBITS);
inflate(&stream, Z_FINISH);
inflateEnd(&stream);
return stream.total_out;
}
#endif /* __CC65__ */
/*
* Structure of a GZIP file:
*
* 1. GZIP header:
* Offset 0: Signature (2 bytes: 0x1f, 0x8b)
* Offset 2: Compression method (1 byte: 8 == "deflate")
* Offset 3: Flags (1 byte: see below)
* Offset 4: File date and time (4 bytes)
* Offset 8: Extra flags (1 byte)
* Offset 9: Target OS (1 byte: DOS, Amiga, Unix, etc.)
* if (flags & FEXTRA) { 2 bytes of length, then length bytes }
* if (flags & FNAME) { ASCIIZ filename }
* if (flags & FCOMMENT) { ASCIIZ comment }
* if (flags & FHCRC) { 2 bytes of CRC }
*
* 2. Deflate compressed data.
*
* 3. GZIP trailer:
* Offset 0: CRC-32 (4 bytes)
* Offset 4: uncompressed file length (4 bytes)
*/
/* Flags in the GZIP header. */
#define FTEXT 1 /* Extra text */
#define FHCRC 2 /* Header CRC */
#define FEXTRA 4 /* Extra field */
#define FNAME 8 /* File name */
#define FCOMMENT 16 /* File comment */
/*
* We read whole GZIP file into this buffer.
* Then we use this buffer for the decompressed data.
*/
static unsigned char buffer[26000];
/*
* Get a 16-bit little-endian unsigned number, using unsigned char* p.
* On many machines this could be (*(unsigned short*) p),
* but I really like portability. :-)
*/
#define GET_WORD(p) (*(p) + ((unsigned) (p)[1] << 8))
/* Likewise, for a 32-bit number. */
#define GET_LONG(p) (GET_WORD(p) + ((unsigned long) GET_WORD(p + 2) << 16))
/*
* Uncompress a GZIP file.
* On entry, buffer[] should contain the whole GZIP file contents,
* and the argument complen should be equal to the length of the GZIP file.
* On return, buffer[] contains the uncompressed data, and the returned
* value is the length of the uncompressed data.
*/
unsigned uncompress_buffer(unsigned complen)
{
unsigned char* ptr;
unsigned long crc;
unsigned long unclen;
void* ptr2;
unsigned unclen2;
/* check GZIP signature */
if (buffer[0] != 0x1f || buffer[1] != 0x8b) {
puts("Not GZIP format");
return 0;
}
/* check compression method (it is always (?) "deflate") */
if (buffer[2] != 8) {
puts("Unsupported compression method");
return 0;
}
/* get CRC from GZIP trailer */
crc = GET_LONG(buffer + complen - 8);
/* get uncompressed length from GZIP trailer */
unclen = GET_LONG(buffer + complen - 4);
if (unclen > sizeof(buffer)) {
puts("Uncompressed size too big");
return 0;
}
/* skip extra field, file name, comment and crc */
ptr = buffer + 10;
if (buffer[3] & FEXTRA)
ptr = buffer + 12 + GET_WORD(buffer + 10);
if (buffer[3] & FNAME)
while (*ptr++ != 0);
if (buffer[3] & FCOMMENT)
while (*ptr++ != 0);
if (buffer[3] & FHCRC)
ptr += 2;
/*
* calculate length of raw "deflate" data
* (without the GZIP header and 8-byte trailer)
*/
complen -= (ptr - buffer) + 8;
/*
* We will move the compressed data to the end of buffer[].
* Thus the compressed data and the decompressed data (written from
* the beginning of buffer[]) may overlap, as long as the decompressed
* data doesn't go further than unread compressed data.
* ptr2 points to the beginning of compressed data at the end
* of buffer[].
*/
ptr2 = buffer + sizeof(buffer) - complen;
/* move the compressed data to end of buffer[] */
memmove(ptr2, ptr, complen);
/* uncompress */
puts("Inflating...");
unclen2 = inflatemem(buffer, ptr2);
/* verify uncompressed length */
if (unclen2 != (unsigned) unclen) {
puts("Uncompressed size does not match");
return 0;
}
/* verify CRC */
puts("Calculating CRC...");
if (crc32(crc32(0L, Z_NULL, 0), buffer, unclen2) != crc) {
puts("CRC mismatch");
return 0;
}
/* return number of uncompressed bytes */
return unclen2;
}
/*
* Get a filename from standard input.
*/
char* get_fname(void)
{
static char filename[100];
unsigned len;
fgets(filename, sizeof(filename), stdin);
len = strlen(filename);
if (len >= 1 && filename[len - 1] == '\n')
filename[len - 1] = '\0';
return filename;
}
int main(void)
{
FILE* fp;
unsigned length;
/* read GZIP file */
puts("GZIP file name:");
fp = fopen(get_fname(), "rb");
if (!fp) {
puts("Can't open GZIP file");
return 1;
}
length = fread(buffer, 1, sizeof(buffer), fp);
fclose(fp);
if (length == sizeof(buffer)) {
puts("File is too long");
return 1;
}
/* decompress */
length = uncompress_buffer(length);
if (length == 0)
return 1;
/* write uncompressed file */
puts("Uncompressed file name:");
fp = fopen(get_fname(), "wb");
if (!fp) {
puts("Can't create output file");
return 1;
}
if (fwrite(buffer, 1, length, fp) != length) {
puts("Error while writing output file");
return 1;
}
fclose(fp);
puts("Ok.");
return 0;
}