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shcomp.c
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shcomp.c
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/*
Implementation of the shannon compressor.
Emanuele Acri - crossbower@gmail.com - 2015
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <assert.h>
/*
Global running options
*/
struct {
uint16_t bits; /* size of the data chunks */
char *in_fname; /* input file name */
char *out_fname; /* output file name */
} opts;
/*
Descriptor of a chunk of data
*/
typedef struct {
uint16_t bits; /* size of the data in bits */
uint32_t count; /* count of the occurrences in file */
uint8_t *p; /* pointer to the data */
} chunk_t;
/*
Global chunk table
*/
struct {
uint32_t count; /* number of different chunks */
uint32_t total; /* total number of allocated entries */
chunk_t *chunks; /* chunk array */
} table;
/*
Add a chunk to the global table,
or increase the count if it already exists
*/
void
add_chunk (uint8_t *chunk, uint16_t bits)
{
uint32_t i, j, m;
int r = 0;
assert(chunk);
assert(bits > 0);
i = 0;
j = table.count - 1;
m = 0;
if(table.count) {
while(i < j) {
m = i + ((j - i) / 2);
r = memcmp(table.chunks[m].p, chunk, bits/8 + (bits % 8 > 0 ? 1 : 0));
if(r == 0) {
table.chunks[m].count++;
return;
}
else if (r > 0) j = m;
else i = m;
}
if(i == j) {
m = i;
r = memcmp(table.chunks[m].p, chunk, bits/8 + (bits % 8 > 0 ? 1 : 0));
if(r == 0) {
table.chunks[m].count++;
return;
}
}
}
if(table.total == table.count) {
if(table.total == 0) table.total = 1;
table.chunks = realloc(table.chunks,
table.total * 2 * sizeof(*table.chunks));
assert(table.chunks != NULL);
table.total *= 2;
}
memmove(table.chunks + (m + 1) * sizeof(*table.chunks),
table.chunks + m * sizeof(*table.chunks),
(table.count - m) * sizeof(*table.chunks));
table.chunks[m].count = 1;
table.chunks[m].bits = bits;
table.chunks[m].p = calloc(1, bits/8 + 1);
memcpy(table.chunks[m].p, chunk, bits/8 + 1);
table.count++;
}
/*
Print, in a human readable form, the global chunk table.
*/
void
print_chunk_table ()
{
uint32_t i;
printf("total chunks: %d\n", table.count);
for(i = 0; i < table.count; i++) {
/* TODO: print bits value */
printf("%u\t%u\n", i, table.chunks[i].count);
}
}
/*
Read 8 bits from a file (at a given bit offset).
Returns the number of bits read.
*/
uint8_t
read_8_bits (FILE *fp, uint8_t *out, uint64_t offset)
{
uint8_t byte;
if(fseek(fp, offset / 8, SEEK_SET) != 0)
return 0;
if(fread(&byte, 1, 1, fp) < 1)
return 0;
*out = byte << (offset % 8);
if(fread(&byte, 1, 1, fp) < 1)
return 8 - (offset % 8);
*out |= byte >> (8 - (offset % 8));
return 8;
}
/*
Write 1 to 8 bits to a file (at a given bit offset).
Note: maintain an internal variable containing trailing
bits to write to the next byte, for non byte-aligned
writes.
Note: To flush the trailing bits call the function
with count set to zero.
Returns the number of bits written.
TODO: carefully check this...
*/
uint8_t
write_8_bits (FILE *fp, uint8_t *in, uint8_t count)
{
static uint8_t saved_byte = 0, trailing_bits = 0;
assert(count <= 8);
if(count == 0 && trailing_bits > 0) {
if(fwrite(&saved_byte, 1, 1, fp) < 1)
return 0;
saved_byte = 0;
trailing_bits = 0;
return 8;
}
else if(count + trailing_bits < 8) {
saved_byte |= (*in >> trailing_bits);
saved_byte &= 0xff << (8 - trailing_bits - count);
trailing_bits += count;
return 0;
}
else if(count + trailing_bits >= 8) {
uint8_t byte;
byte = saved_byte | *in >> trailing_bits;
if(fwrite(&byte, 1, 1, fp) < 1)
return 0;
saved_byte = *in << (8 - trailing_bits);
saved_byte &= 0xff << ((8 - count) + (8 - trailing_bits));
trailing_bits = count - (8 - trailing_bits);
return 8;
}
return 0;
}
/*
Read a chunk from a file.
Note: maintains an internal bit offset
to read non-byte aligned chunks.
Returns the number of bits read.
*/
uint16_t
read_chunk (FILE *fp, uint8_t *dst, uint16_t bits)
{
uint16_t bits_read = 0;
uint8_t r;
static uint64_t offset = 0;
if(bits < 1)
return 0;
while(bits > 0) {
r = read_8_bits(fp, dst, offset);
bits_read += bits < r ? bits : r;
offset += bits < r ? bits : r;
dst++;
bits -= bits < r ? bits : r;
if(r < 8) break;
}
return bits_read;
}
/*
Write a chunk to a file.
Note: see the note of write_8_bits,
since it is a dependency of this function.
Returns the number of bits written.
*/
uint16_t
write_chunk (FILE *fp, uint8_t *src, uint16_t bits)
{
uint16_t bits_written = 0;
if(bits < 1)
return 0;
while(bits > 0) {
write_8_bits(fp, src, bits > 8 ? 8 : bits);
/* TODO: check errors */
bits_written += bits < 8 ? bits : 8;
src++;
bits -= bits < 8 ? bits : 8;
}
return bits_written;
}
void
usage (char *progname)
{
printf("Usage: %s bits in_file out_file\n", progname);
}
int
main (int argc, char *argv[])
{
FILE *fin, *fout;
uint8_t *buffer;
uint16_t r;
if(argc < 4) {
usage(argv[0]);
return 1;
}
opts.bits = atoi(argv[1]);
opts.in_fname = argv[2];
opts.out_fname = argv[3];
memset(&table, 0, sizeof(table));
fin = fopen(opts.in_fname, "r");
if(fin == NULL) {
perror("fopen: ");
return 1;
}
buffer = calloc(1, opts.bits/8 + 1);
do {
puts(".");
r = read_chunk(fin, buffer, opts.bits);
if(r == 0) break;
add_chunk(buffer, r);
print_chunk_table();
} while(r == opts.bits);
print_chunk_table();
fclose(fin);
return 0;
}