ref: 52cacba37c6f3a125ef931afa4b9c2cdb7438fef
dir: /sys/src/cmd/disk/sacfs/sac.c/
#include <u.h>
#include <libc.h>
#include <bio.h>
#include "sac.h"
#include "ssort.h"
typedef struct Chain Chain;
typedef struct Chains Chains;
typedef struct Huff Huff;
enum
{
ZBase = 2, /* base of code to encode 0 runs */
LitBase = ZBase-1, /* base of literal values */
MaxLit = 256,
MaxLeaf = MaxLit+LitBase,
MaxHuffBits = 16, /* limit of bits in a huffman code */
ChainMem = 2 * (MaxHuffBits - 1) * MaxHuffBits,
};
/*
* huffman code table
*/
struct Huff
{
short bits; /* length of the code */
ulong encode; /* the code */
};
struct Chain
{
ulong count; /* occurances of everything in the chain */
ushort leaf; /* leaves to the left of chain, or leaf value */
char col; /* ref count for collecting unused chains */
char gen; /* need to generate chains for next lower level */
Chain *up; /* Chain up in the lists */
};
struct Chains
{
Chain *lists[(MaxHuffBits - 1) * 2];
ulong leafcount[MaxLeaf]; /* sorted list of leaf counts */
ushort leafmap[MaxLeaf]; /* map to actual leaf number */
int nleaf; /* number of leaves */
Chain chains[ChainMem];
Chain *echains;
Chain *free;
char col;
int nlists;
};
static jmp_buf errjmp;
static uchar *bout;
static int bmax;
static int bpos;
static ulong leafcount[MaxLeaf];
static ulong nzero;
static ulong *hbuf;
static int hbpos;
static ulong nzero;
static ulong maxblocksym;
static void henc(int);
static void hbflush(void);
static void mkprecode(Huff*, ulong *, int, int);
static ulong sendtab(Huff *tab, int maxleaf, ushort *map);
static int elimBits(int b, ulong *bused, char *tmtf, int maxbits);
static void elimBit(int b, char *tmtf, int maxbits);
static void nextchain(Chains*, int);
static void hufftabinit(Huff*, int, ulong*, int);
static void leafsort(ulong*, ushort*, int, int);
static void bitput(int, int);
static int mtf(uchar*, int);
static void fatal(char*, ...);
static ulong headerbits;
static ulong charmapbits;
static ulong hufftabbits;
static ulong databits;
static ulong nbits;
static ulong bits;
int
sac(uchar *dst, uchar *src, int n)
{
uchar front[256];
ulong *perm, cmap[256];
long i, c, rev;
rev = 0;
perm = nil;
if(setjmp(errjmp)){
free(perm);
if(rev){
for(i = 0; i < n/2; i++){
c = src[i];
src[i] = src[n-i-1];
src[n-i-1] = c;
}
}
return -1;
}
/*
* set up the output buffer
*/
bout = dst;
bmax = n;
bpos = 0;
perm = malloc((n+1)*sizeof *perm);
if(perm == nil)
return -1;
hbuf = perm;
hbpos = 0;
nbits = 0;
nzero = 0;
for(i = 0; i < MaxLeaf; i++)
leafcount[i] = 0;
if(rev){
for(i = 0; i < n/2; i++){
c = src[i];
src[i] = src[n-i-1];
src[n-i-1] = c;
}
}
i = ssortbyte(src, (int*)perm, nil, n);
headerbits += 16;
bitput(i, 16);
/*
* send the map of chars which occur in this block
*/
for(i = 0; i < 256; i++)
cmap[i] = 0;
for(i = 0; i < n; i++)
cmap[src[i]] = 1;
charmapbits += 1;
bitput(cmap[0] != 0, 1);
for(i = 0; i < 256; i = c){
for(c = i + 1; c < 256 && (cmap[c] != 0) == (cmap[i] != 0); c++)
;
charmapbits += 8;
bitput(c - i - 1, 8);
}
/*
* initialize mtf state
*/
c = 0;
for(i = 0; i < 256; i++){
if(cmap[i]){
cmap[i] = c;
front[c] = i;
c++;
}
}
maxblocksym = c + LitBase;
for(i = 0; i <= n; i++){
c = perm[i] - 1;
if(c < 0)
continue;
henc(mtf(front, src[c]));
}
hbflush();
bitput(0, 24);
bitput(0, 8 - nbits);
free(perm);
return bpos;
}
static void
bitput(int c, int n)
{
bits <<= n;
bits |= c;
for(nbits += n; nbits >= 8; nbits -= 8){
c = bits << (32 - nbits);
if(bpos >= bmax)
longjmp(errjmp, 1);
bout[bpos++] = c >> 24;
}
}
static int
mtf(uchar *front, int c)
{
int i, v;
for(i = 0; front[i] != c; i++)
;
for(v = i; i > 0; i--)
front[i] = front[i - 1];
front[0] = c;
return v;
}
/*
* encode a run of zeros
* convert to funny run length coding:
* add one, omit implicit top 1 bit.
*/
static void
zenc(void)
{
int m;
nzero++;
while(nzero != 1){
m = nzero & 1;
hbuf[hbpos++] = m;
leafcount[m]++;
nzero >>= 1;
}
nzero = 0;
}
/*
* encode one symbol
*/
static void
henc(int c)
{
if(c == 0){
nzero++;
return;
}
if(nzero)
zenc();
c += LitBase;
leafcount[c]++;
hbuf[hbpos++] = c;
}
static void
hbflush(void)
{
Huff tab[MaxLeaf];
int i, b, s;
if(nzero)
zenc();
if(hbpos == 0)
return;
mkprecode(tab, leafcount, maxblocksym, MaxHuffBits);
hufftabbits += sendtab(tab, maxblocksym, nil);
/*
* send the data
*/
for(i = 0; i < hbpos; i++){
s = hbuf[i];
b = tab[s].bits;
if(b == 0)
fatal("bad tables %d", i);
databits += b;
bitput(tab[s].encode, b);
}
}
static ulong
sendtab(Huff *tab, int maxleaf, ushort *map)
{
ulong ccount[MaxHuffBits+1], bused[MaxHuffBits+1];
Huff codetab[MaxHuffBits+1];
char tmtf[MaxHuffBits+1];
ulong bits;
int i, b, max, ttb, s, elim;
/*
* make up the table table
* over cleverness: the data is known to be a huffman table
* check for fullness at each bit level, and wipe it out from
* the possibilities; when nothing exists except 0, stop.
*/
for(i = 0; i <= MaxHuffBits; i++){
tmtf[i] = i;
ccount[i] = 0;
bused[i] = 0;
}
tmtf[0] = -1;
tmtf[MaxHuffBits] = 0;
elim = 0;
for(i = 0; i < maxleaf && elim != MaxHuffBits; i++){
b = i;
if(map)
b = map[b];
b = tab[b].bits;
for(s = 0; tmtf[s] != b; s++)
if(s >= MaxHuffBits)
fatal("bitlength not found");
ccount[s]++;
for(; s > 0; s--)
tmtf[s] = tmtf[s-1];
tmtf[0] = b;
elim += elimBits(b, bused, tmtf, MaxHuffBits);
}
if(elim != MaxHuffBits && elim != 0)
fatal("incomplete huffman table");
/*
* make up and send the table table
*/
max = 8;
mkprecode(codetab, ccount, MaxHuffBits+1, max);
for(i = 0; i <= max; i++){
tmtf[i] = i;
bused[i] = 0;
}
tmtf[0] = -1;
tmtf[max] = 0;
elim = 0;
bits = 0;
for(i = 0; i <= MaxHuffBits && elim != max; i++){
b = codetab[i].bits;
for(s = 0; tmtf[s] != b; s++)
if(s > max)
fatal("bitlength not found");
ttb = 4;
while(max - elim < (1 << (ttb-1)))
ttb--;
bits += ttb;
bitput(s, ttb);
elim += elimBits(b, bused, tmtf, max);
}
if(elim != max)
fatal("incomplete huffman table table");
/*
* send the table
*/
for(i = 0; i <= MaxHuffBits; i++){
tmtf[i] = i;
bused[i] = 0;
}
tmtf[0] = -1;
tmtf[MaxHuffBits] = 0;
elim = 0;
for(i = 0; i < maxleaf && elim != MaxHuffBits; i++){
b = i;
if(map)
b = map[b];
b = tab[b].bits;
for(s = 0; tmtf[s] != b; s++)
if(s >= MaxHuffBits)
fatal("bitlength not found");
ttb = codetab[s].bits;
if(ttb < 0)
fatal("bad huffman table table");
bits += ttb;
bitput(codetab[s].encode, ttb);
for(; s > 0; s--)
tmtf[s] = tmtf[s-1];
tmtf[0] = b;
elim += elimBits(b, bused, tmtf, MaxHuffBits);
}
if(elim != MaxHuffBits && elim != 0)
fatal("incomplete huffman table");
return bits;
}
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
elimBit(int b, char *tmtf, int maxbits)
{
int bb;
for(bb = 0; bb < maxbits; bb++)
if(tmtf[bb] == b)
break;
if(tmtf[bb] != b)
fatal("elim bit not found");
while(++bb <= maxbits)
tmtf[bb - 1] = tmtf[bb];
}
/*
* fast?, in-place huffman codes
*
* A. Moffat, J. Katajainen, "In-Place Calculation of Minimum-Redundancy Codes",
*
* counts must be sorted, and may be aliased to bitlens
*/
static int
fmkprecode(ulong *bitcount, ulong *bitlen, ulong *counts, int n, int maxbits)
{
int leaf, tree, treet, depth, nodes, internal;
/*
* form the internal tree structure:
* [0, tree) are parent pointers,
* [tree, treet) are weights of internal nodes,
* [leaf, n) are weights of remaining leaves.
*
* note that at the end, there are n-1 internal nodes
*/
leaf = 0;
tree = 0;
for(treet = 0; treet != n - 1; treet++){
if(leaf >= n || tree < treet && bitlen[tree] < counts[leaf]){
bitlen[treet] = bitlen[tree];
bitlen[tree++] = treet;
}else
bitlen[treet] = counts[leaf++];
if(leaf >= n || tree < treet && bitlen[tree] < counts[leaf]){
bitlen[treet] += bitlen[tree];
bitlen[tree++] = treet;
}else
bitlen[treet] += counts[leaf++];
}
if(tree != treet - 1)
fatal("bad fast mkprecode");
/*
* calculate depth of internal nodes
*/
bitlen[n - 2] = 0;
for(tree = n - 3; tree >= 0; tree--)
bitlen[tree] = bitlen[bitlen[tree]] + 1;
/*
* calculate depth of leaves:
* at each depth, leaves(depth) = nodes(depth) - internal(depth)
* and nodes(depth+1) = 2 * internal(depth)
*/
leaf = n;
tree = n - 2;
depth = 0;
for(nodes = 1; nodes > 0; nodes = 2 * internal){
internal = 0;
while(tree >= 0 && bitlen[tree] == depth){
tree--;
internal++;
}
nodes -= internal;
if(depth < maxbits)
bitcount[depth] = nodes;
while(nodes-- > 0)
bitlen[--leaf] = depth;
depth++;
}
if(leaf != 0 || tree != -1)
fatal("bad leaves in fast mkprecode");
return depth - 1;
}
/*
* fast, low space overhead algorithm for max depth huffman type codes
*
* J. Katajainen, A. Moffat and A. Turpin, "A fast and space-economical
* algorithm for length-limited coding," Proc. Intl. Symp. on Algorithms
* and Computation, Cairns, Australia, Dec. 1995, Lecture Notes in Computer
* Science, Vol 1004, J. Staples, P. Eades, N. Katoh, and A. Moffat, eds.,
* pp 12-21, Springer Verlag, New York, 1995.
*/
static void
mkprecode(Huff *tab, ulong *count, int n, int maxbits)
{
Chains cs;
Chain *c;
ulong bitcount[MaxHuffBits];
int i, m, em, bits;
/*
* set up the sorted list of leaves
*/
m = 0;
for(i = 0; i < n; i++){
tab[i].bits = -1;
tab[i].encode = 0;
if(count[i] != 0){
cs.leafcount[m] = count[i];
cs.leafmap[m] = i;
m++;
}
}
if(m < 2){
if(m != 0){
m = cs.leafmap[0];
tab[m].bits = 0;
tab[m].encode = 0;
}
return;
}
cs.nleaf = m;
leafsort(cs.leafcount, cs.leafmap, 0, m);
/*
* try fast code
*/
bits = fmkprecode(bitcount, cs.leafcount, cs.leafcount, m, maxbits);
if(bits < maxbits){
for(i = 0; i < m; i++)
tab[cs.leafmap[i]].bits = cs.leafcount[i];
bitcount[0] = 0;
}else{
for(i = 0; i < m; i++)
cs.leafcount[i] = count[cs.leafmap[i]];
/*
* set up free list
*/
cs.free = &cs.chains[2];
cs.echains = &cs.chains[ChainMem];
cs.col = 1;
/*
* initialize chains for each list
*/
c = &cs.chains[0];
c->count = cs.leafcount[0];
c->leaf = 1;
c->col = cs.col;
c->up = nil;
c->gen = 0;
cs.chains[1] = cs.chains[0];
cs.chains[1].leaf = 2;
cs.chains[1].count = cs.leafcount[1];
for(i = 0; i < maxbits-1; i++){
cs.lists[i * 2] = &cs.chains[0];
cs.lists[i * 2 + 1] = &cs.chains[1];
}
cs.nlists = 2 * (maxbits - 1);
m = 2 * m - 2;
for(i = 2; i < m; i++)
nextchain(&cs, cs.nlists - 2);
bits = 0;
bitcount[0] = cs.nleaf;
for(c = cs.lists[cs.nlists - 1]; c != nil; c = c->up){
m = c->leaf;
bitcount[bits++] -= m;
bitcount[bits] = m;
}
m = 0;
for(i = bits; i >= 0; i--)
for(em = m + bitcount[i]; m < em; m++)
tab[cs.leafmap[m]].bits = i;
}
hufftabinit(tab, n, bitcount, bits);
}
/*
* calculate the next chain on the list
* we can always toss out the old chain
*/
static void
nextchain(Chains *cs, int list)
{
Chain *c, *oc;
int i, nleaf, sumc;
oc = cs->lists[list + 1];
cs->lists[list] = oc;
if(oc == nil)
return;
/*
* make sure we have all chains needed to make sumc
* note it is possible to generate only one of these,
* use twice that value for sumc, and then generate
* the second if that preliminary sumc would be chosen.
* however, this appears to be slower on current tests
*/
if(oc->gen){
nextchain(cs, list - 2);
nextchain(cs, list - 2);
oc->gen = 0;
}
/*
* pick up the chain we're going to add;
* collect unused chains no free ones are left
*/
for(c = cs->free; ; c++){
if(c >= cs->echains){
cs->col++;
for(i = 0; i < cs->nlists; i++)
for(c = cs->lists[i]; c != nil; c = c->up)
c->col = cs->col;
c = cs->chains;
}
if(c->col != cs->col)
break;
}
/*
* pick the cheapest of
* 1) the next package from the previous list
* 2) the next leaf
*/
nleaf = oc->leaf;
sumc = 0;
if(list > 0 && cs->lists[list-1] != nil)
sumc = cs->lists[list-2]->count + cs->lists[list-1]->count;
if(sumc != 0 && (nleaf >= cs->nleaf || cs->leafcount[nleaf] > sumc)){
c->count = sumc;
c->leaf = oc->leaf;
c->up = cs->lists[list-1];
c->gen = 1;
}else if(nleaf >= cs->nleaf){
cs->lists[list + 1] = nil;
return;
}else{
c->leaf = nleaf + 1;
c->count = cs->leafcount[nleaf];
c->up = oc->up;
c->gen = 0;
}
cs->free = c + 1;
cs->lists[list + 1] = c;
c->col = cs->col;
}
static void
hufftabinit(Huff *tab, int n, ulong *bitcount, int nbits)
{
ulong code, nc[MaxHuffBits];
int i, bits;
code = 0;
for(bits = 1; bits <= nbits; bits++){
code = (code + bitcount[bits-1]) << 1;
nc[bits] = code;
}
for(i = 0; i < n; i++){
bits = tab[i].bits;
if(bits > 0)
tab[i].encode = nc[bits]++;
}
}
static int
pivot(ulong *c, int a, int n)
{
int j, pi, pj, pk;
j = n/6;
pi = a + j; /* 1/6 */
j += j;
pj = pi + j; /* 1/2 */
pk = pj + j; /* 5/6 */
if(c[pi] < c[pj]){
if(c[pi] < c[pk]){
if(c[pj] < c[pk])
return pj;
return pk;
}
return pi;
}
if(c[pj] < c[pk]){
if(c[pi] < c[pk])
return pi;
return pk;
}
return pj;
}
static void
leafsort(ulong *leafcount, ushort *leafmap, int a, int n)
{
ulong t;
int j, pi, pj, pn;
while(n > 1){
if(n > 10){
pi = pivot(leafcount, a, n);
}else
pi = a + (n>>1);
t = leafcount[pi];
leafcount[pi] = leafcount[a];
leafcount[a] = t;
t = leafmap[pi];
leafmap[pi] = leafmap[a];
leafmap[a] = t;
pi = a;
pn = a + n;
pj = pn;
for(;;){
do
pi++;
while(pi < pn && (leafcount[pi] < leafcount[a] || leafcount[pi] == leafcount[a] && leafmap[pi] > leafmap[a]));
do
pj--;
while(pj > a && (leafcount[pj] > leafcount[a] || leafcount[pj] == leafcount[a] && leafmap[pj] < leafmap[a]));
if(pj < pi)
break;
t = leafcount[pi];
leafcount[pi] = leafcount[pj];
leafcount[pj] = t;
t = leafmap[pi];
leafmap[pi] = leafmap[pj];
leafmap[pj] = t;
}
t = leafcount[a];
leafcount[a] = leafcount[pj];
leafcount[pj] = t;
t = leafmap[a];
leafmap[a] = leafmap[pj];
leafmap[pj] = t;
j = pj - a;
n = n-j-1;
if(j >= n){
leafsort(leafcount, leafmap, a, j);
a += j+1;
}else{
leafsort(leafcount, leafmap, a + (j+1), n);
n = j;
}
}
}
static void
fatal(char *fmt, ...)
{
char buf[512];
va_list arg;
va_start(arg, fmt);
doprint(buf, buf+sizeof(buf), fmt, arg);
va_end(arg);
longjmp(errjmp, 1);
}