pgpztrees.c

vc环境下的pgp源码

				DIST_BUFSIZE * sizeof(PGPUInt16), kPGPMemoryMgrFlags_Clear);
    if (ctx->d_buf == NULL) {
		pgpContextMemFree (cdkContext, ctx);
		return NULL;
	}
    ctx->l_buf = (PGPByte far *)pgpContextMemAlloc (cdkContext,
				(LIT_BUFSIZE/2) * 2, kPGPMemoryMgrFlags_Clear);
    /* Avoid using the value 64K on 16 bit machines */
    if (ctx->l_buf == NULL) {
		pgpContextMemFree (cdkContext, ctx->d_buf);
		pgpContextMemFree (cdkContext, ctx);
		return NULL;
    }
/*    if (ctx->l_buf == NULL || ctx->d_buf == NULL)
 *		  error("ct_init: out of memory");
 */
#endif
    /* Initialize the counts for the first block */
    init_block(ctx);

    /* The following initializes constant data - it may be skipped */
    if (ctx->static_dtree[0].Len != 0) return 0; /* ct_init already called */

    /* Initialize the mapping length (0..255) -> length code (0..28) */
    length = 0;
    for (code = 0; code < LENGTH_CODES-1; code++) {
		ctx->base_length[code] = length;
		for (n = 0; n < (1<<extra_lbits[code]); n++) {
			ctx->length_code[length++] = (PGPByte)code;
		}
    }
    ZipAssert (length == 256, "ct_init: length != 256");
    /* Note that the length 255 (match length 258) can be represented
     * in two different ways: code 284 + 5 bits or code 285, so we
     * overwrite length_code[255] to use the best encoding:
     */
    ctx->length_code[length-1] = (PGPByte)code;

    /* Initialize the mapping dist (0..32K) -> dist code (0..29) */
    dist = 0;
    for (code = 0 ; code < 16; code++) {
		ctx->base_dist[code] = dist;
		for (n = 0; n < (1<<extra_dbits[code]); n++) {
			ctx->dist_code[dist++] = (PGPByte)code;
		}
    }
    ZipAssert (dist == 256, "ct_init: dist != 256");
    dist >>= 7; /* from now on, all distances are divided by 128 */
    for ( ; code < D_CODES; code++) {
		ctx->base_dist[code] = dist << 7;
		for (n = 0; n < (1<<(extra_dbits[code]-7)); n++) {
			ctx->dist_code[256 + dist++] = (PGPByte)code;
		}
    }
    ZipAssert (dist == 256, "ct_init: 256+dist != 512");

    /* Construct the codes of the static literal tree */
    for (bits = 0; bits <= MAX_BITS; bits++)
		ctx->bl_count[bits] = 0;
    n = 0;
    while (n <= 143) ctx->static_ltree[n++].Len = 8, ctx->bl_count[8]++;
    while (n <= 255) ctx->static_ltree[n++].Len = 9, ctx->bl_count[9]++;
    while (n <= 279) ctx->static_ltree[n++].Len = 7, ctx->bl_count[7]++;
    while (n <= 287) ctx->static_ltree[n++].Len = 8, ctx->bl_count[8]++;
    /* Codes 286 and 287 do not exist, but we must include them in the
     * tree construction to get a canonical Huffman tree (longest code
     * all ones)
     */
    gen_codes(ctx, (ct_data near *)ctx->static_ltree, L_CODES+1);

    /* The static distance tree is trivial: */
    for (n = 0; n < D_CODES; n++) {
		ctx->static_dtree[n].Len = 5;
		ctx->static_dtree[n].Code = bit_reverse(n, 5);
    }

    return ctx;
}

void ct_free(ZTreesContext *ctx)
{
	PGPContextRef cdkContext;

	cdkContext = ctx->cdkContext;

#ifdef DYN_ALLOC
    /* Wipe and free buffers */
    pgpClearMemory(ctx->d_buf, DIST_BUFSIZE * sizeof(PGPUInt16));
    pgpClearMemory(ctx->l_buf, LIT_BUFSIZE);
    pgpContextMemFree (cdkContext, ctx->d_buf);
    pgpContextMemFree (cdkContext, ctx->l_buf);
#endif

    /* Wipe everything else */
	pgpClearMemory( ctx, sizeof(*ctx) );
	pgpContextMemFree( cdkContext, ctx );
}

/* ===========================================================================
 * Initialize a new block.
 */
static void
init_block(ZTreesContext *ctx)
{
    int n; /* iterates over tree elements */

    /* Initialize the trees. */
    for (n = 0; n < L_CODES;  n++) ctx->dyn_ltree[n].Freq = 0;
    for (n = 0; n < D_CODES;  n++) ctx->dyn_dtree[n].Freq = 0;
    for (n = 0; n < BL_CODES; n++) ctx->bl_tree[n].Freq = 0;

    ctx->dyn_ltree[END_BLOCK].Freq = 1;
    ctx->opt_len = ctx->static_len = 0L;
    ctx->last_lit = ctx->last_dist = ctx->last_flags = 0;
    ctx->flags = 0; ctx->flag_bit = 1;
}

#define SMALLEST 1
/* Index within the heap array of least frequent node in the Huffman tree */


/* ===========================================================================
 * Remove the smallest element from the heap and recreate the heap with
 * one less element. Updates heap and heap_len.
 */
#define pqremove(ctx, tree, top) \
{\
    top = (ctx)->heap[SMALLEST]; \
    (ctx)->heap[SMALLEST] = (ctx)->heap[(ctx)->heap_len--]; \
    pqdownheap(ctx, tree, SMALLEST); \
}

/* ===========================================================================
 * Compares to subtrees, using the tree depth as tie breaker when
 * the subtrees have equal frequency. This minimizes the worst case length.
 */
#define smaller(ctx, tree, n, m) \
   (tree[n].Freq < tree[m].Freq || \
   (tree[n].Freq == tree[m].Freq && (ctx)->depth[n] <= (ctx)->depth[m]))

/* ===========================================================================
 * Restore the heap property by moving down the tree starting at node k,
 * exchanging a node with the smallest of its two sons if necessary, stopping
 * when the heap property is re-established (each father smaller than its
 * two sons).
 */
static void
pqdownheap(ZTreesContext *ctx, ct_data near *tree, int k)
{
    int v = ctx->heap[k];
    int j = k << 1;  /* left son of k */
    int htemp;       /* required because of bug in SASC compiler */

    while (j <= ctx->heap_len) {
        /* Set j to the smallest of the two sons: */
        if (j < ctx->heap_len && smaller(ctx, tree, ctx->heap[j+1],
										 ctx->heap[j])) j++;

        /* Exit if v is smaller than both sons */
        htemp = ctx->heap[j];
        if (smaller(ctx, tree, v, htemp)) break;

        /* Exchange v with the smallest son */
		ctx->heap[k] = htemp;
        k = j;

        /* And continue down the tree, setting j to the left son of k */
        j <<= 1;
    }
    ctx->heap[k] = v;
}

/* ===========================================================================
 * Compute the optimal bit lengths for a tree and update the total bit length
 * for the current block.
 * IN assertion: the fields freq and dad are set, heap[heap_max] and
 *    above are the tree nodes sorted by increasing frequency.
 * OUT assertions: the field len is set to the optimal bit length, the
 *     array bl_count contains the frequencies for each bit length.
 *     The length opt_len is updated; static_len is also updated if stree is
 *     not null.
 */
static void
gen_bitlen(ZTreesContext *ctx, tree_desc near *desc)
{
    ct_data near *tree  = desc->dyn_tree;
    int const near *extra      = desc->extra_bits;
    int base                   = desc->extra_base;
    int max_code               = desc->max_code;
    int max_length             = desc->max_length;
    ct_data near *stree = desc->static_tree;
    int h;              /* heap index */
    int n, m;           /* iterate over the tree elements */
    int bits;           /* bit length */
    int xbits;          /* extra bits */
    PGPUInt16 f;           /* frequency */
    int overflow = 0;   /* number of elements with bit length too large */

    for (bits = 0; bits <= MAX_BITS; bits++)
        ctx->bl_count[bits] = 0;

    /* In a first pass, compute the optimal bit lengths (which may
     * overflow in the case of the bit length tree).
     */
    tree[ctx->heap[ctx->heap_max]].Len = 0; /* root of the heap */

    for (h = ctx->heap_max+1; h < HEAP_SIZE; h++) {
        n = ctx->heap[h];
        bits = tree[tree[n].Dad].Len + 1;
        if (bits > max_length) {
            bits = max_length;
            overflow++;
		}
        tree[n].Len = (PGPUInt16)bits;
        /* We overwrite tree[n].Dad which is no longer needed */

        if (n > max_code)
            continue; /* not a leaf node */

        ctx->bl_count[bits]++;
        xbits = 0;
        if (n >= base)
            xbits = extra[n-base];
        f = tree[n].Freq;
        ctx->opt_len += (PGPUInt32)f * (bits + xbits);
        if (stree)
            ctx->static_len += (PGPUInt32)f * (stree[n].Len + xbits);
    }
    if (overflow == 0) return;

    Trace((stderr,"\nbit length overflow\n"));
    /* This happens for example on obj2 and pic of the Calgary corpus */

    /* Find the first bit length which could increase: */
    do {
        bits = max_length-1;
        while (ctx->bl_count[bits] == 0)
            bits--;
        ctx->bl_count[bits]--;      /* move one leaf down the tree */
        ctx->bl_count[bits+1] += 2; /* move one overflow item as its brother */
        ctx->bl_count[max_length]--;
        /* The brother of the overflow item also moves one step up,
         * but this does not affect bl_count[max_length]
         */
        overflow -= 2;
    } while (overflow > 0);

    /* Now recompute all bit lengths, scanning in increasing frequency.
     * h is still equal to HEAP_SIZE. (It is simpler to reconstruct all
     * lengths instead of fixing only the wrong ones. This idea is taken
     * from 'ar' written by Haruhiko Okumura.)
     */
    for (bits = max_length; bits != 0; bits--) {
        n = ctx->bl_count[bits];
        while (n != 0) {
            m = ctx->heap[--h];
            if (m > max_code)
                continue;
            if (tree[m].Len != (unsigned) bits) {
                Trace((stderr,"code %d bits %d->%d\n", m, tree[m].Len, bits));
                ctx->opt_len += ((long)bits - tree[m].Len) * tree[m].Freq;
                tree[m].Len = (PGPUInt16)bits;
            }
            n--;
        }
    }
}

/* ===========================================================================
 * Generate the codes for a given tree and bit counts (which need not be
 * optimal).
 * IN assertion: the array bl_count contains the bit length statistics for
 *    the given tree and the field len is set for all tree elements.
 * OUT assertion: the field code is set for all tree elements of non
 *     zero code length.
 */
static void
gen_codes(ZTreesContext *ctx, ct_data near *tree, int max_code)
{
    PGPUInt16 next_code[MAX_BITS+1]; /* next code value for each bit length */
    PGPUInt16 code = 0;              /* running code value */
    int bits;                     /* bit index */
    int n;                        /* code index */

    /* The distribution counts are first used to generate the code values
     * without bit reversal.
     */
    for (bits = 1; bits <= MAX_BITS; bits++)
        next_code[bits] = code = (code + ctx->bl_count[bits-1]) << 1;
    /* Check that the bit counts in bl_count are consistent. The last code
     * must be all ones.
     */
    ZipAssert (code + ctx->bl_count[MAX_BITS]-1 == (1<<MAX_BITS)-1,
            "inconsistent bit counts");
    Tracev((stderr,"\ngen_codes: max_code %d ", max_code));

    for (n = 0;  n <= max_code; n++) {
        int len = tree[n].Len;
        if (len == 0)
            continue;
        /* Now reverse the bits */
        tree[n].Code = bit_reverse(next_code[len]++, len);

		Tracec(tree != static_ltree, (stderr,"\nn %3d %c l %2d c %4x (%x) ",
             n, (isgraph(n) ? n : ' '), len, tree[n].Code, next_code[len]-1));
    }
}

/* ===========================================================================
 * Construct one Huffman tree and assigns the code bit strings and lengths.
 * Update the total bit length for the current block.
 * IN assertion: the field freq is set for all tree elements.
 * OUT assertions: the fields len and code are set to the optimal bit length
 *     and corresponding code. The length opt_len is updated; static_len is
 *     also updated if stree is not null. The field max_code is set.
 */
static void
build_tree(ZTreesContext *ctx, tree_desc near *desc)
{
    ct_data near *tree   = desc->dyn_tree;
    ct_data near *stree  = desc->static_tree;
    int elems            = desc->elems;
    int n, m;          /* iterate over heap elements */
    int max_code = -1; /* largest code with non zero frequency */
    int node = elems;  /* next internal node of the tree */

    /* Construct the initial heap, with least frequent element in
     * heap[SMALLEST]. The sons of heap[n] are heap[2*n] and heap[2*n+1].
     * heap[0] is not used.
     */
    ctx->heap_len = 0, ctx->heap_max = HEAP_SIZE;

    for (n = 0; n < elems; n++) {
        if (tree[n].Freq != 0) {
            ctx->heap[++ctx->heap_len] = max_code = n;
            ctx->depth[n] = 0;
		} else {
            tree[n].Len = 0;
		}
    }

    /* The pkzip format requires that at least one distance code exists,
     * and that at least one bit should be sent even if there is only one
     * possible code. So to avoid special checks later on we force at least
     * two codes of non zero frequency.
     */
    while (ctx->heap_len < 2) {
        n = ctx->heap[++ctx->heap_len] = (max_code < 2 ? ++max_code : 0);
        tree[n].Freq = 1;
        ctx->depth[n] = 0;
        ctx->opt_len--;
        if (stree)
            ctx->static_len -= stree[n].Len;
        /* n is 0 or 1 so it does not have extra bits */
    }
    desc->max_code = max_code;

    /* The elements heap[heap_len/2+1 .. heap_len] are leaves of the tree,
     * establish sub-heaps of increasing lengths:
     */
    for (n = ctx->heap_len/2; n >= 1; n--)
        pqdownheap(ctx, tree, n);

    /* Construct the Huffman tree by repeatedly combining the least two
     * frequent nodes.
     */
    do {
        pqremove(ctx, tree, n);   /* n = node of least frequency */
        m = ctx->heap[SMALLEST];  /* m = node of next least frequency */

        ctx->heap[--ctx->heap_max] = n; /* keep the nodes sorted by frequency*/
        ctx->heap[--ctx->heap_max] = m;

        /* Create a new node father of n and m */
		tree[node].Freq = tree[n].Freq + tree[m].Freq;
        ctx->depth[node] = (PGPByte)(MAX(ctx->depth[n], ctx->depth[m]) + 1);
        tree[n].Dad = tree[m].Dad = (PGPUInt16)node;
#ifdef DUMP_BL_TREE
        if (tree == ctx->bl_tree)
            fprintf(stderr,"\nnode %d(%d), sons %d(%d) %d(%d)",
                    node, tree[node].Freq, n, tree[n].Freq, m, tree[m].Freq);
#endif
        /* and insert the new node in the heap */
        ctx->heap[SMALLEST] = node++;
        pqdownheap(ctx, tree, SMALLEST);

    } while (ctx->heap_len >= 2);

    ctx->heap[--ctx->heap_max] = ctx->heap[SMALLEST];

    /* At this point, the fields freq and dad are set. We can now
     * generate the bit lengths.
     */
    gen_bitlen(ctx, desc);

    /* The field len is now set, we can generate the bit codes */
    gen_codes (ctx, tree, max_code);
}

/* ===========================================================================
 * Scan a literal or distance tree to determine the frequencies of the codes
 * in the bit length tree. Updates opt_len to take into account the repeat
 * counts.  (The contribution of the bit length codes will be added later
 * during the construction of bl_tree.)
 */
static void