harvey/sys/src/cmd/gs/src/sbwbs.c

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  she says so in writing.  Refer to the Aladdin Free Public License (the
  "License") for full details.
  
  Every copy of AFPL Ghostscript must include a copy of the License, normally
  in a plain ASCII text file named PUBLIC.  The License grants you the right
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  requires that the copyright notice and this notice be preserved on all
  copies.
*/

/*$Id: sbwbs.c,v 1.2 2000/09/19 19:00:48 lpd Exp $ */
/* Burrows/Wheeler block sorting compression filters */
#include "stdio_.h"
#include "memory_.h"
#include <stdlib.h>		/* for qsort */
#include "gdebug.h"
#include "strimpl.h"
#include "sfilter.h"
#include "sbwbs.h"

/* ------ Common code for streams that buffer a block ------ */

private_st_buffered_state();

/* Initialize */
private void
s_buffered_set_defaults(stream_state * st)
{
    stream_buffered_state *const ss = (stream_buffered_state *) st;

    /* Clear pointers */
    ss->buffer = 0;
}
private int
s_buffered_no_block_init(stream_state * st)
{
    stream_buffered_state *const ss = (stream_buffered_state *) st;

    ss->buffer = 0;
    ss->filling = true;
    ss->bpos = 0;
    return 0;
}
private int
s_buffered_block_init(stream_state * st)
{
    stream_buffered_state *const ss = (stream_buffered_state *) st;

    s_buffered_no_block_init(st);
    ss->buffer = gs_alloc_bytes(st->memory, ss->BlockSize, "buffer");
    if (ss->buffer == 0)
	return ERRC;
/****** WRONG ******/
    return 0;
}

/* Continue filling the buffer if needed. */
/* Return 0 if the buffer isn't full yet, 1 if it is full or if */
/* we reached the end of input data. */
/* In the latter case, also set filling = false. */
/* Note that this procedure doesn't take pw as an argument. */
private int
s_buffered_process(stream_state * st, stream_cursor_read * pr, bool last)
{
    stream_buffered_state *const ss = (stream_buffered_state *) st;
    register const byte *p = pr->ptr;
    const byte *rlimit = pr->limit;
    uint count = rlimit - p;
    uint left = ss->bsize - ss->bpos;

    if (!ss->filling)
	return 1;
    if (left < count)
	count = left;
    if_debug3('w', "[w]buffering %d bytes to position %d, last = %s\n",
	      count, ss->bpos, (last ? "true" : "false"));
    memcpy(ss->buffer + ss->bpos, p + 1, count);
    pr->ptr = p += count;
    ss->bpos += count;
    if (ss->bpos == ss->bsize || (p == rlimit && last)) {
	ss->filling = false;
	return 1;
    }
    return 0;
}

/* Release */
private void
s_buffered_release(stream_state * st)
{
    stream_buffered_state *const ss = (stream_buffered_state *) st;

    gs_free_object(st->memory, ss->buffer, "buffer");
}

/* ------ Common code for Burrows/Wheeler block sorting filters ------ */

private_st_BWBS_state();
private void s_BWBS_release(P1(stream_state *));

/* Set default parameter values (actually, just clear pointers). */
private void
s_BWBS_set_defaults(stream_state * st)
{
    stream_BWBS_state *const ss = (stream_BWBS_state *) st;

    s_buffered_set_defaults(st);
    ss->offsets = 0;
}

/* Initialize */
private int
bwbs_init(stream_state * st, uint osize)
{
    stream_BWBS_state *const ss = (stream_BWBS_state *) st;
    int code;

    ss->bsize = ss->BlockSize;
    code = s_buffered_block_init(st);
    if (code != 0)
	return code;
    ss->offsets = (void *)gs_alloc_bytes(st->memory, osize,
					 "BWBlockSort offsets");
    if (ss->offsets == 0) {
	s_BWBS_release(st);
	return ERRC;
/****** WRONG ******/
    }
    ss->I = -1;			/* haven't read I yet */
    return 0;
}

/* Release the filter. */
private void
s_BWBS_release(stream_state * st)
{
    stream_BWBS_state *const ss = (stream_BWBS_state *) st;

    gs_free_object(st->memory, ss->offsets, "BWBlockSort offsets");
    s_buffered_release(st);
}

/* ------ BWBlockSortEncode ------ */

/* Initialize */
private int
s_BWBSE_init(stream_state * st)
{
    stream_BWBS_state *const ss = (stream_BWBS_state *) st;

    return bwbs_init(st, ss->BlockSize * sizeof(int));
}

/* Compare two rotated strings for sorting. */
private stream_BWBS_state *bwbs_compare_ss;
private int
bwbs_compare_rotations(const void *p1, const void *p2)
{
    const byte *buffer = bwbs_compare_ss->buffer;
    const byte *s1 = buffer + *(const int *)p1;
    const byte *s2 = buffer + *(const int *)p2;
    const byte *start1;
    const byte *end;
    int swap;

    if (*s1 != *s2)
	return (*s1 < *s2 ? -1 : 1);
    if (s1 < s2)
	swap = 1;
    else {
	const byte *t = s1;

	s1 = s2;
	s2 = t;
	swap = -1;
    }
    start1 = s1;
    end = buffer + bwbs_compare_ss->N;
    for (s1++, s2++; s2 < end; s1++, s2++)
	if (*s1 != *s2)
	    return (*s1 < *s2 ? -swap : swap);
    s2 = buffer;
    for (; s1 < end; s1++, s2++)
	if (*s1 != *s2)
	    return (*s1 < *s2 ? -swap : swap);
    s1 = buffer;
    for (; s1 < start1; s1++, s2++)
	if (*s1 != *s2)
	    return (*s1 < *s2 ? -swap : swap);
    return 0;
}
/* Sort the strings. */
private void
bwbse_sort(const byte * buffer, uint * indices, int N)
{
    offsets_full Cs;

#define C Cs.v
    /* Sort the strings.  We start with a radix sort. */
    uint sum = 0, j, ch;

    memset(C, 0, sizeof(Cs));
    for (j = 0; j < N; j++)
	C[buffer[j]]++;
    for (ch = 0; ch <= 255; ch++) {
	sum += C[ch];
	C[ch] = sum - C[ch];
    }
    for (j = 0; j < N; j++)
	indices[C[buffer[j]]++] = j;
    /* Now C[ch] = the number of strings that start */
    /* with a character less than or equal to ch. */
    sum = 0;
    /* qsort each bucket produced by the radix sort. */
    for (ch = 0; ch <= 255; sum = C[ch], ch++)
	qsort(indices + sum, C[ch] - sum,
	      sizeof(*indices),
	      bwbs_compare_rotations);
#undef C
}

/* Encode a buffer */
private int
s_BWBSE_process(stream_state * st, stream_cursor_read * pr,
		stream_cursor_write * pw, bool last)
{
    stream_BWBS_state *const ss = (stream_BWBS_state *) st;
    register byte *q = pw->ptr;
    byte *wlimit = pw->limit;
    uint wcount = wlimit - q;
    uint *indices = ss->offsets;

    if (ss->filling) {
	int status, j, N;
	byte *buffer = ss->buffer;
	if (wcount < sizeof(int) * 2)
	        return 1;

	/* Continue filling the buffer. */
	status = s_buffered_process(st, pr, last);
	if (!status)
	    return 0;
	ss->N = N = ss->bpos;
	/* We reverse the string before encoding it, */
	/* so it will come out of the decoder correctly. */
	for (j = N / 2 - 1; j >= 0; j--) {
	    byte *p0 = &buffer[j];
	    byte *p1 = &buffer[N - 1 - j];
	    byte b = *p0;

	    *p0 = *p1;
	    *p1 = b;
	}
	/* Save st in a static, because that's the only way */
	/* we can pass it to the comparison procedure (ugh). */
	bwbs_compare_ss = ss;
	/* Sort the strings. */
	bwbse_sort(buffer, indices, N);
	/* Find the unrotated string. */
	for (j = 0; j < N; j++)
	    if (indices[j] == 0) {
		ss->I = j;
		break;
	    }
	for (j = sizeof(int); --j >= 0;)
	    *++q = (byte) (N >> (j * 8));
	for (j = sizeof(int); --j >= 0;)
	    *++q = (byte) (ss->I >> (j * 8));
	ss->bpos = 0;
    }
    /* We're reading out of the buffer, writing the permuted string. */
    while (q < wlimit && ss->bpos < ss->N) {
	int i = indices[ss->bpos++];

	*++q = ss->buffer[(i == 0 ? ss->N - 1 : i - 1)];
    }
    if (ss->bpos == ss->N) {
	ss->filling = true;
	ss->bpos = 0;
    }
    pw->ptr = q;
    if (q == wlimit)
	return 1;
    return 0;
}

/* Stream template */
const stream_template s_BWBSE_template = {
    &st_BWBS_state, s_BWBSE_init, s_BWBSE_process, sizeof(int) * 2, 1,
    s_BWBS_release, s_BWBS_set_defaults
};

/* ------ BWBlockSortDecode ------ */

#define SHORT_OFFSETS

#ifdef SHORT_OFFSETS

/*
 * Letting S[0..N-1] be the data block before depermutation, we need
 * a table P[0..N-1] that maps the index i to O(S[i],i), where O(c,i) is
 * the number of occurrences of c in S before position i.
 * We observe that for a fixed c, O(c,i) is monotonic with i,
 * and falls in the range 0 .. i; consequently, if 0 <= i <= j,
 * 0 <= O(c,j) - O(c,i) <= j - i.  Proceeding from this observation,
 * rather than allocate an entire int to each entry of P,
 * we construct three tables as follows:
 *      P2[k,c] = O(c,k*65536) for k = 0 .. (N-1)/65536;
 *              each entry requires an int.
 *      P1[k,c] = O(c,k*4096) - P2[k/16,c] for k = 0 .. (N-1)/4096;
 *              each entry falls in the range 0 .. 15*4096 and hence
 *              requires 16 bits.
 *      P0[i] = O(S[i],i) - P1[i/4096,S[i]] for i = 0 .. N-1;
 *              each entry falls in the range 0 .. 4095 and hence
 *              requires 12 bits.
 * Since the value we need in the decompression loop is actually
 * P[i] + C[S[i]], where C[c] is the sum of O(0,N) ... O(c-1,N),
 * we add C[c] into P2[k,c] for all k.
 */
							/*typedef struct { uint v[256]; } offsets_full; *//* in sbwbs.h */
typedef struct {
    bits16 v[256];
} offsets_4k;

#if arch_sizeof_int > 2
#  define ceil_64k(n) (((n) + 0xffff) >> 16)
#else
#  define ceil_64k(n) 1
#endif
#define ceil_4k(n) (((n) + 0xfff) >> 12)
#define offset_space(bsize)\
  (ceil_64k(bsize) * sizeof(offsets_full) +\
   ceil_4k(bsize) * sizeof(offsets_4k) +\
   ((bsize + 1) >> 1) * 3)

#else /* !SHORT_OFFSETS */

#define offset_space(bsize)\
  (bsize * sizeof(int))

#endif /* (!)SHORT_OFFSETS */

/* Initialize */
private int
s_BWBSD_init(stream_state * st)
{
    stream_BWBS_state *const ss = (stream_BWBS_state *) st;
    uint bsize = ss->BlockSize;

    return bwbs_init(st, offset_space(bsize));
}

/* Construct the decoding tables. */

#ifdef SHORT_OFFSETS

private void
bwbsd_construct_offsets(stream_BWBS_state * sst, offsets_full * po64k,
			offsets_4k * po4k, byte * po1, int N)
{
    offsets_full Cs;

#define C Cs.v
    uint i1;
    byte *b = sst->buffer;
    offsets_full *p2 = po64k - 1;
    offsets_4k *p1 = po4k;
    byte *p0 = po1;

    memset(C, 0, sizeof(Cs));
    for (i1 = 0; i1 < ceil_4k(N); i1++, p1++) {
	int j;

	if (!(i1 & 15))
	    *++p2 = Cs;
	for (j = 0; j < 256; j++)
	    p1->v[j] = C[j] - p2->v[j];
	j = (N + 1 - (i1 << 12)) >> 1;
	if (j > 4096 / 2)
	    j = 4096 / 2;
	for (; j > 0; j--, b += 2, p0 += 3) {
	    byte b0 = b[0];
	    uint d0 = C[b0]++ - (p1->v[b0] + p2->v[b0]);
	    byte b1 = b[1];
	    uint d1 = C[b1]++ - (p1->v[b1] + p2->v[b1]);

	    p0[0] = d0 >> 4;
	    p0[1] = (byte) ((d0 << 4) + (d1 >> 8));
	    p0[2] = (byte) d1;
	}
    }
    /* If the block length is odd, discount the extra byte. */
    if (N & 1)
	C[sst->buffer[N]]--;
    /* Compute the cumulative totals in C. */
    {
	int sum = 0, ch;

	for (ch = 0; ch <= 255; ch++) {
	    sum += C[ch];
	    C[ch] = sum - C[ch];
	}
    }
    /* Add the C values back into the 64K table, */
    /* which saves an addition of C[b] in the decoding loop. */
    {
	int i2, ch;

	for (p2 = po64k, i2 = ceil_64k(N); i2 > 0; p2++, i2--)
	    for (ch = 0; ch < 256; ch++)
		p2->v[ch] += C[ch];
    }
#undef C
}

#else /* !SHORT_OFFSETS */

private void
bwbsd_construct_offsets(stream_BWBS_state * sst, int *po, int N)
{
    offsets_full Cs;

#define C Cs.v
    uint i;
    byte *b = sst->buffer;
    int *p = po;

    memset(C, 0, sizeof(Cs));
    for (i = 0; i < N; i++, p++, b++)
	*p = C[*b]++;
    /* Compute the cumulative totals in C. */
    {
	int sum = 0, ch;

	for (ch = 0; ch <= 255; ch++) {
	    sum += C[ch];
	    C[ch] = sum - C[ch];
	}
    }
    /* Add the C values back into the offsets. */
    for (i = 0, b = sst->buffer, p = po; i < N; i++, b++, p++)
	*p += C[*b];
#undef C
}

#endif /* (!)SHORT_OFFSETS */

/* Decode a buffer */
private int
s_BWBSD_process(stream_state * st, stream_cursor_read * pr,
		stream_cursor_write * pw, bool last)
{
    stream_BWBS_state *const ss = (stream_BWBS_state *) st;
    register const byte *p = pr->ptr;
    const byte *rlimit = pr->limit;
    uint count = rlimit - p;
    register byte *q = pw->ptr;
    byte *wlimit = pw->limit;

#ifdef SHORT_OFFSETS
    uint BlockSize = ss->BlockSize;
    offsets_full *po64k = ss->offsets;
    offsets_4k *po4k = (offsets_4k *) (po64k + ceil_64k(BlockSize));
    byte *po1 = (byte *) (po4k + ceil_4k(BlockSize));

#else /* !SHORT_OFFSETS */
    int *po = ss->offsets;

#endif /* (!)SHORT_OFFSETS */

    if (ss->I < 0) {		/* Read block parameters */
	int I, N, j;
	if (count < sizeof(int) * 2)
	        return 0;
	for (N = 0, j = 0; j < sizeof(int); j++)

	    N = (N << 8) + *++p;
	for (I = 0, j = 0; j < sizeof(int); j++)

	    I = (I << 8) + *++p;
	ss->N = N;
	ss->I = I;
	if_debug2('w', "[w]N=%d I=%d\n", N, I);
	pr->ptr = p;
	if (N < 0 || N > ss->BlockSize || I < 0 || I >= N)
	    return ERRC;
	if (N == 0)
	    return EOFC;
	count -= sizeof(int) * 2;

	ss->bpos = 0;
	ss->bsize = N;
    }
    if (ss->filling) {		/* Continue filling the buffer. */
	if (!s_buffered_process(st, pr, last))
	    return 0;
	/* Construct the inverse sort order. */
#ifdef SHORT_OFFSETS
	bwbsd_construct_offsets(ss, po64k, po4k, po1, ss->bsize);
#else /* !SHORT_OFFSETS */
	bwbsd_construct_offsets(ss, po, ss->bsize);
#endif /* (!)SHORT_OFFSETS */
	ss->bpos = 0;
	ss->i = ss->I;
    }
    /* We're reading out of the buffer. */
    while (q < wlimit && ss->bpos < ss->bsize) {
	int i = ss->i;
	byte b = ss->buffer[i];

#ifdef SHORT_OFFSETS
	uint d;
	const byte *pd = &po1[(i >> 1) + i];

	*++q = b;
	if (!(i & 1))
	    d = ((uint) pd[0] << 4) + (pd[1] >> 4);
	else
	    d = ((pd[0] & 0xf) << 8) + pd[1];
	ss->i = po64k[i >> 16].v[b] + po4k[i >> 12].v[b] + d;
#else /* !SHORT_OFFSETS */
	*++q = b;
	ss->i = po[i];
#endif /* (!)SHORT_OFFSETS */
	ss->bpos++;
    }
    if (ss->bpos == ss->bsize) {
	ss->I = -1;
	ss->filling = true;
    }
    pw->ptr = q;
    if (q == wlimit)
	return 1;
    return 0;
}

/* Stream template */
const stream_template s_BWBSD_template = {
    &st_BWBS_state, s_BWBSD_init, s_BWBSD_process, 1, sizeof(int) * 2,
    s_BWBS_release, s_BWBS_set_defaults
};