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Weissman lzcsaw.c
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#include <stdio.h> | |
#include <stdlib.h> | |
#include <string.h> | |
#include <err.h> | |
#include <sys/stat.h> | |
#include <assert.h> | |
#define MAX_RUN_BYTES 9 | |
#define NUM_RUNS (1<<20) | |
#define MASK (0xffff) | |
#define HASH_LEN 4 | |
typedef struct { | |
uint8_t len; | |
char bytes[MAX_RUN_BYTES]; | |
} run_t; | |
run_t runs[NUM_RUNS] = { { 0, {0} } }; | |
#pragma pack(push, 1) | |
typedef struct _backref { | |
uint8_t lit : 1; | |
uint8_t len : 7; | |
uint16_t hash; | |
} backref_t; | |
typedef struct _literal { | |
uint8_t lit : 1; | |
uint8_t len : 7; | |
} literal_t; | |
#pragma pack(pop) | |
unsigned int first_difference(char *one, char *two) | |
{ | |
unsigned int i = 0; | |
while (one[i] == two[i] && i < MAX_RUN_BYTES) | |
i++; | |
return i; | |
} | |
uint16_t do_hash(const char *str) | |
{ | |
unsigned int hash = 0x55aa55aa; | |
unsigned int i = 0; | |
for(i = 0; i < HASH_LEN; str++, i++) | |
{ | |
hash ^= ((hash << 5) + (*str) + (hash >> 2)); | |
} | |
return hash & MASK; | |
} | |
void clear_runs() | |
{ | |
for (unsigned int i = 0; i < NUM_RUNS; i++) | |
{ | |
memset(&runs[i], 0, sizeof(run_t)); | |
} | |
} | |
char *compress(const char *input, unsigned int *out_size) | |
{ | |
clear_runs(); | |
struct stat st; | |
if (stat(input, &st) < 0) | |
err(2, "Stat failed"); | |
char *in = (char *)malloc(st.st_size); | |
FILE *fp = fopen(input, "rb"); | |
if (!fp) | |
err(3, "Couldn't open file"); | |
fread(in, 1, st.st_size, fp); | |
fclose(fp); | |
// Output in will be no bigger than file | |
char *out = (char *)malloc(st.st_size); | |
memset(out, 0, st.st_size); | |
printf("%p\n", out); | |
unsigned int ii = 0; | |
unsigned int oi = 0; | |
do { | |
// hash 4 bytes of input | |
uint16_t hash = do_hash(&in[ii]); | |
unsigned int max_len = first_difference(&in[ii], runs[hash].bytes); | |
// see if its in the hash table | |
if (runs[hash].len != 0 && max_len >= HASH_LEN) { | |
// if so, find the longest run | |
// emit backref with length and hash | |
assert(max_len >= HASH_LEN); | |
backref_t backref; | |
memset(&backref, 0, sizeof(backref)); | |
backref.lit = 0; | |
backref.len = max_len; | |
backref.hash = hash; | |
memcpy(&out[oi], &backref, sizeof(backref)); | |
oi += sizeof(backref); | |
// replace hash table bytes | |
memcpy(runs[hash].bytes, &in[ii], max_len); | |
runs[hash].len = max_len; | |
ii += max_len; | |
} else { | |
// if not in hash, emit a literal and add to hash table | |
literal_t literal; | |
memset(&literal, 0, sizeof(literal)); | |
literal.lit = 1; | |
literal.len = MAX_RUN_BYTES; | |
memcpy(&out[oi], &literal, sizeof(literal)); | |
oi += sizeof(literal); | |
memcpy(&out[oi], &in[ii], literal.len); | |
oi += literal.len; | |
runs[hash].len = literal.len; | |
memcpy(runs[hash].bytes, &in[ii], literal.len); | |
ii += literal.len; | |
} | |
} while (ii < st.st_size); | |
*out_size = oi; | |
free(in); | |
return out; | |
} | |
char *decompress(const char *in, const unsigned int input_size, unsigned int *decompressed_size) | |
{ | |
clear_runs(); | |
unsigned int ii = 0; | |
unsigned int oi = 0; | |
unsigned int out_size = 0; | |
literal_t maybe_lit; | |
backref_t backref; | |
// Calculate output size | |
do { | |
memcpy(&maybe_lit, &in[ii], sizeof(maybe_lit)); | |
if (maybe_lit.lit) { | |
ii += sizeof(maybe_lit) + maybe_lit.len; | |
out_size += maybe_lit.len; | |
} else { | |
ii += sizeof(backref); | |
out_size += maybe_lit.len; | |
} | |
} while (ii < input_size); | |
*decompressed_size = out_size; | |
char *out = (char *)malloc(out_size); | |
memset(out, 0, out_size); | |
ii = 0; | |
oi = 0; | |
do { | |
memcpy(&maybe_lit, &in[ii], sizeof(maybe_lit)); | |
if (maybe_lit.lit) { | |
ii += sizeof(maybe_lit); | |
uint16_t hash = do_hash(&in[ii]); | |
runs[hash].len = maybe_lit.len; | |
memcpy(&runs[hash].bytes, &in[ii], maybe_lit.len); | |
memcpy(&out[oi], &in[ii], maybe_lit.len); | |
ii += maybe_lit.len; | |
oi += maybe_lit.len; | |
} else { | |
memcpy(&backref, &in[ii], sizeof(backref)); | |
ii += sizeof(backref); | |
memcpy(&out[oi], &runs[backref.hash].bytes, backref.len); | |
oi += maybe_lit.len; | |
} | |
} while (ii < input_size); | |
return out; | |
} | |
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