ref: 52cacba37c6f3a125ef931afa4b9c2cdb7438fef
dir: /sys/src/cmd/disk/sacfs/unsac.c/
#include <u.h>
#include <libc.h>
#include "sac.h"
typedef struct Huff Huff;
typedef struct Mtf Mtf;
typedef struct Decode Decode;
enum
{
ZBase = 2, /* base of code to encode 0 runs */
LitBase = ZBase-1, /* base of literal values */
MaxLit = 256,
MaxLeaf = MaxLit+LitBase,
MaxHuffBits = 16, /* max bits in a huffman code */
MaxFlatbits = 5, /* max bits decoded in flat table */
CombLog = 4,
CombSpace = 1 << CombLog, /* mtf speedup indices spacing */
CombMask = CombSpace - 1,
};
struct Mtf
{
int maxcomb; /* index of last valid comb */
uchar prev[MaxLit];
uchar next[MaxLit];
uchar comb[MaxLit / CombSpace + 1];
};
struct Huff
{
int maxbits;
int flatbits;
ulong flat[1<<MaxFlatbits];
ulong maxcode[MaxHuffBits];
ulong last[MaxHuffBits];
ulong decode[MaxLeaf];
};
struct Decode{
Huff tab;
Mtf mtf;
int nbits;
ulong bits;
int nzero;
int base;
ulong maxblocksym;
jmp_buf errjmp;
uchar *src; /* input buffer */
uchar *smax; /* limit */
};
static void fatal(Decode *dec, char*);
static int hdec(Decode*);
static void recvtab(Decode*, Huff*, int, ushort*);
static ulong bitget(Decode*, int);
static int mtf(uchar*, int);
#define FORWARD 0
static void
mtflistinit(Mtf *m, uchar *front, int n)
{
int last, me, f, i, comb;
if(n == 0)
return;
/*
* add all entries to free list
*/
last = MaxLit - 1;
for(i = 0; i < MaxLit; i++){
m->prev[i] = last;
m->next[i] = i + 1;
last = i;
}
m->next[last] = 0;
f = 0;
/*
* pull valid entries off free list and enter into mtf list
*/
comb = 0;
last = front[0];
for(i = 0; i < n; i++){
me = front[i];
f = m->next[me];
m->prev[f] = m->prev[me];
m->next[m->prev[f]] = f;
m->next[last] = me;
m->prev[me] = last;
last = me;
if((i & CombMask) == 0)
m->comb[comb++] = me;
}
/*
* pad out the list with dummies to the next comb,
* using free entries
*/
for(; i & CombMask; i++){
me = f;
f = m->next[me];
m->prev[f] = m->prev[me];
m->next[m->prev[f]] = f;
m->next[last] = me;
m->prev[me] = last;
last = me;
}
me = front[0];
m->next[last] = me;
m->prev[me] = last;
m->comb[comb] = me;
m->maxcomb = comb;
}
static int
mtflist(Mtf *m, int pos)
{
uchar *next, *prev, *mycomb;
int c, c0, pc, nc, off;
if(pos == 0)
return m->comb[0];
next = m->next;
prev = m->prev;
mycomb = &m->comb[pos >> CombLog];
off = pos & CombMask;
if(off >= CombSpace / 2){
c = mycomb[1];
for(; off < CombSpace; off++)
c = prev[c];
}else{
c = *mycomb;
for(; off; off--)
c = next[c];
}
nc = next[c];
pc = prev[c];
prev[nc] = pc;
next[pc] = nc;
for(; mycomb > m->comb; mycomb--)
*mycomb = prev[*mycomb];
c0 = *mycomb;
*mycomb = c;
mycomb[m->maxcomb] = c;
next[c] = c0;
pc = prev[c0];
prev[c] = pc;
prev[c0] = c;
next[pc] = c;
return c;
}
static void
hdecblock(Decode *dec, ulong n, ulong I, uchar *buf, ulong *sums, ulong *prev)
{
ulong i, nn, sum;
int m, z, zz, c;
nn = I;
n--;
i = 0;
again:
for(; i < nn; i++){
while((m = hdec(dec)) == 0 && i + dec->nzero < n)
;
if(z = dec->nzero){
dec->nzero = 0;
c = dec->mtf.comb[0];
sum = sums[c];
sums[c] = sum + z;
z += i;
zz = z;
if(i < I && z > I){
zz = I;
z++;
}
zagain:
for(; i < zz; i++){
buf[i] = c;
prev[i] = sum++;
}
if(i != z){
zz = z;
nn = ++n;
i++;
goto zagain;
}
if(i == nn){
if(i == n)
return;
nn = ++n;
i++;
}
}
c = mtflist(&dec->mtf, m);
buf[i] = c;
sum = sums[c];
prev[i] = sum++;
sums[c] = sum;
}
if(i == n)
return;
nn = ++n;
i++;
goto again;
}
int
unsac(uchar *dst, uchar *src, int n, int nsrc)
{
Decode *dec;
uchar *buf, *front;
ulong *prev, *sums;
ulong sum, i, I;
int m, j, c;
dec = malloc(sizeof *dec);
buf = malloc(n+2);
prev = malloc((n+2) * sizeof *prev);
front = malloc(MaxLit * sizeof *front);
sums = malloc(MaxLit * sizeof *sums);
if(dec == nil || buf == nil || prev == nil || front == nil || sums == nil || setjmp(dec->errjmp)){
free(dec);
free(buf);
free(prev);
free(front);
free(sums);
return -1;
}
dec->src = src;
dec->smax = src + nsrc;
dec->nbits = 0;
dec->bits = 0;
dec->nzero = 0;
for(i = 0; i < MaxLit; i++)
front[i] = i;
n++;
I = bitget(dec, 16);
if(I >= n)
fatal(dec, "corrupted input");
/*
* decode the character usage map
*/
for(i = 0; i < MaxLit; i++)
sums[i] = 0;
c = bitget(dec, 1);
for(i = 0; i < MaxLit; ){
m = bitget(dec, 8) + 1;
while(m--){
if(i >= MaxLit)
fatal(dec, "corrupted char map");
front[i++] = c;
}
c = c ^ 1;
}
/*
* initialize mtf state
*/
c = 0;
for(i = 0; i < MaxLit; i++)
if(front[i])
front[c++] = i;
mtflistinit(&dec->mtf, front, c);
dec->maxblocksym = c + LitBase;
/*
* huffman decoding, move to front decoding,
* along with character counting
*/
dec->base = 1;
recvtab(dec, &dec->tab, MaxLeaf, nil);
hdecblock(dec, n, I, buf, sums, prev);
sum = 1;
for(i = 0; i < MaxLit; i++){
c = sums[i];
sums[i] = sum;
sum += c;
}
i = 0;
for(j = n - 2; j >= 0; j--){
if(i > n || i < 0 || i == I)
fatal(dec, "corrupted data");
c = buf[i];
dst[j] = c;
i = prev[i] + sums[c];
}
free(dec);
free(buf);
free(prev);
free(front);
free(sums);
return n;
}
static ulong
bitget(Decode *dec, int nb)
{
int c;
while(dec->nbits < nb){
if(dec->src >= dec->smax)
fatal(dec, "premature eof 1");
c = *dec->src++;
dec->bits <<= 8;
dec->bits |= c;
dec->nbits += 8;
}
dec->nbits -= nb;
return (dec->bits >> dec->nbits) & ((1 << nb) - 1);
}
static void
fillbits(Decode *dec)
{
int c;
while(dec->nbits < 24){
if(dec->src >= dec->smax)
fatal(dec, "premature eof 2");
c = *dec->src++;
dec->bits <<= 8;
dec->bits |= c;
dec->nbits += 8;
}
}
/*
* decode one symbol
*/
static int
hdecsym(Decode *dec, Huff *h, int b)
{
long c;
ulong bits;
int nbits;
bits = dec->bits;
nbits = dec->nbits;
for(; (c = bits >> (nbits - b)) > h->maxcode[b]; b++)
;
if(b > h->maxbits)
fatal(dec, "too many bits consumed");
dec->nbits = nbits - b;
return h->decode[h->last[b] - c];
}
static int
hdec(Decode *dec)
{
ulong c;
int nbits, nb;
if(dec->nbits < dec->tab.maxbits)
fillbits(dec);
nbits = dec->nbits;
dec->bits &= (1 << nbits) - 1;
c = dec->tab.flat[dec->bits >> (nbits - dec->tab.flatbits)];
nb = c & 0xff;
c >>= 8;
if(nb == 0xff)
c = hdecsym(dec, &dec->tab, c);
else
dec->nbits = nbits - nb;
/*
* reverse funny run-length coding
*/
if(c < ZBase){
dec->nzero += dec->base << c;
dec->base <<= 1;
return 0;
}
dec->base = 1;
c -= LitBase;
return c;
}
static void
hufftab(Decode *dec, Huff *h, char *hb, ulong *bitcount, int maxleaf, int maxbits, int flatbits)
{
ulong c, mincode, code, nc[MaxHuffBits];
int i, b, ec;
h->maxbits = maxbits;
if(maxbits < 0)
return;
code = 0;
c = 0;
for(b = 0; b <= maxbits; b++){
h->last[b] = c;
c += bitcount[b];
mincode = code << 1;
nc[b] = mincode;
code = mincode + bitcount[b];
if(code > (1 << b))
fatal(dec, "corrupted huffman table");
h->maxcode[b] = code - 1;
h->last[b] += code - 1;
}
if(code != (1 << maxbits))
fatal(dec, "huffman table not full");
if(flatbits > maxbits)
flatbits = maxbits;
h->flatbits = flatbits;
b = 1 << flatbits;
for(i = 0; i < b; i++)
h->flat[i] = ~0;
/*
* initialize the flat table to include the minimum possible
* bit length for each code prefix
*/
for(b = maxbits; b > flatbits; b--){
code = h->maxcode[b];
if(code == -1)
break;
mincode = code + 1 - bitcount[b];
mincode >>= b - flatbits;
code >>= b - flatbits;
for(; mincode <= code; mincode++)
h->flat[mincode] = (b << 8) | 0xff;
}
for(i = 0; i < maxleaf; i++){
b = hb[i];
if(b == -1)
continue;
c = nc[b]++;
if(b <= flatbits){
code = (i << 8) | b;
ec = (c + 1) << (flatbits - b);
if(ec > (1<<flatbits))
fatal(dec, "flat code too big");
for(c <<= (flatbits - b); c < ec; c++)
h->flat[c] = code;
}else{
c = h->last[b] - c;
if(c >= maxleaf)
fatal(dec, "corrupted huffman table");
h->decode[c] = i;
}
}
}
static void
elimBit(int b, char *tmtf, int maxbits)
{
int bb;
for(bb = 0; bb < maxbits; bb++)
if(tmtf[bb] == b)
break;
while(++bb <= maxbits)
tmtf[bb - 1] = tmtf[bb];
}
static int
elimBits(int b, ulong *bused, char *tmtf, int maxbits)
{
int bb, elim;
if(b < 0)
return 0;
elim = 0;
/*
* increase bits counts for all descendants
*/
for(bb = b + 1; bb < maxbits; bb++){
bused[bb] += 1 << (bb - b);
if(bused[bb] == (1 << bb)){
elim++;
elimBit(bb, tmtf, maxbits);
}
}
/*
* steal bits from parent & check for fullness
*/
for(; b >= 0; b--){
bused[b]++;
if(bused[b] == (1 << b)){
elim++;
elimBit(b, tmtf, maxbits);
}
if((bused[b] & 1) == 0)
break;
}
return elim;
}
static void
recvtab(Decode *dec, Huff *tab, int maxleaf, ushort *map)
{
ulong bitcount[MaxHuffBits+1], bused[MaxHuffBits+1];
char tmtf[MaxHuffBits+1], *hb;
int i, b, ttb, m, maxbits, max, elim;
hb = malloc(MaxLeaf * sizeof *hb);
if(hb == nil)
fatal(dec, "out of memory");
/*
* read the tables for the tables
*/
max = 8;
for(i = 0; i <= MaxHuffBits; i++){
bitcount[i] = 0;
tmtf[i] = i;
bused[i] = 0;
}
tmtf[0] = -1;
tmtf[max] = 0;
elim = 0;
maxbits = -1;
for(i = 0; i <= MaxHuffBits && elim != max; i++){
ttb = 4;
while(max - elim < (1 << (ttb-1)))
ttb--;
b = bitget(dec, ttb);
if(b > max - elim)
fatal(dec, "corrupted huffman table table");
b = tmtf[b];
hb[i] = b;
bitcount[b]++;
if(b > maxbits)
maxbits = b;
elim += elimBits(b, bused, tmtf, max);
}
if(elim != max)
fatal(dec, "incomplete huffman table table");
hufftab(dec, tab, hb, bitcount, i, maxbits, MaxFlatbits);
for(i = 0; i <= MaxHuffBits; i++){
tmtf[i] = i;
bitcount[i] = 0;
bused[i] = 0;
}
tmtf[0] = -1;
tmtf[MaxHuffBits] = 0;
elim = 0;
maxbits = -1;
for(i = 0; i < maxleaf && elim != MaxHuffBits; i++){
if(dec->nbits <= tab->maxbits)
fillbits(dec);
dec->bits &= (1 << dec->nbits) - 1;
m = tab->flat[dec->bits >> (dec->nbits - tab->flatbits)];
b = m & 0xff;
m >>= 8;
if(b == 0xff)
m = hdecsym(dec, tab, m);
else
dec->nbits -= b;
b = tmtf[m];
for(; m > 0; m--)
tmtf[m] = tmtf[m-1];
tmtf[0] = b;
if(b > MaxHuffBits)
fatal(dec, "bit length too big");
m = i;
if(map != nil)
m = map[m];
hb[m] = b;
bitcount[b]++;
if(b > maxbits)
maxbits = b;
elim += elimBits(b, bused, tmtf, MaxHuffBits);
}
if(elim != MaxHuffBits && elim != 0)
fatal(dec, "incomplete huffman table");
if(map != nil)
for(; i < maxleaf; i++)
hb[map[i]] = -1;
hufftab(dec, tab, hb, bitcount, i, maxbits, MaxFlatbits);
free(hb);
}
static void
fatal(Decode *dec, char *msg)
{
print("%s: %s\n", argv0, msg);
longjmp(dec->errjmp, 1);
}