imfhuf.cpp

对gif

///////////////////////////////////////////////////////////////////////////
//
// Copyright (c) 2002, Industrial Light & Magic, a division of Lucas
// Digital Ltd. LLC
// 
// All rights reserved.
// 
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// *       Redistributions in binary form must reproduce the above
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///////////////////////////////////////////////////////////////////////////




//-----------------------------------------------------------------------------
//
//	16-bit Huffman compression and decompression.
//
//	The source code in this file is derived from the 8-bit
//	Huffman compression and decompression routines written
//	by Christian Rouet for his PIZ image file format.
//
//-----------------------------------------------------------------------------

#include <ImfHuf.h>
#include <ImfInt64.h>
#include <ImfAutoArray.h>
#include "Iex.h"
#include <string.h>
#include <assert.h>
#include <algorithm>


using namespace std;
using namespace Iex;

namespace Imf {
namespace {


const int HUF_ENCBITS = 16;			// literal (value) bit length
const int HUF_DECBITS = 14;			// decoding bit size (>= 8)

const int HUF_ENCSIZE = (1 << HUF_ENCBITS) + 1;	// encoding table size
const int HUF_DECSIZE =  1 << HUF_DECBITS;	// decoding table size
const int HUF_DECMASK = HUF_DECSIZE - 1;


struct HufDec
{				// short code		long code
				//-------------------------------
    int		len:8;		// code length		0	 
    int		lit:24;		// lit			p size	 
    int	*	p;		// 0			lits	 
};


void
invalidNBits ()
{
    throw InputExc ("Error in header for Huffman-encoded data "
		    "(invalid number of bits).");
}


void
tooMuchData ()
{
    throw InputExc ("Error in Huffman-encoded data "
		    "(decoded data are longer than expected).");
}


void
notEnoughData ()
{
    throw InputExc ("Error in Huffman-encoded data "
		    "(decoded data are shorter than expected).");
}


void
invalidCode ()
{
    throw InputExc ("Error in Huffman-encoded data "
		    "(invalid code).");
}


void
invalidTableSize ()
{
    throw InputExc ("Error in Huffman-encoded data "
		    "(invalid code table size).");
}


void
unexpectedEndOfTable ()
{
    throw InputExc ("Error in Huffman-encoded data "
		    "(unexpected end of code table data).");
}


void
tableTooLong ()
{
    throw InputExc ("Error in Huffman-encoded data "
		    "(code table is longer than expected).");
}


void
invalidTableEntry ()
{
    throw InputExc ("Error in Huffman-encoded data "
		    "(invalid code table entry).");
}


inline Int64
hufLength (Int64 code)
{
    return code & 63;
}


inline Int64
hufCode (Int64 code)
{
    return code >> 6;
}


inline void
outputBits (int nBits, Int64 bits, Int64 &c, int &lc, char *&out)
{
    c <<= nBits;
    lc += nBits;

    c |= bits;

    while (lc >= 8)
	*out++ = (c >> (lc -= 8));
}


inline Int64
getBits (int nBits, Int64 &c, int &lc, const char *&in)
{
    while (lc < nBits)
    {
	c = (c << 8) | *(unsigned char *)(in++);
	lc += 8;
    }

    lc -= nBits;
    return (c >> lc) & ((1 << nBits) - 1);
}


//
// ENCODING TABLE BUILDING & (UN)PACKING
//

//
// Build a "canonical" Huffman code table:
//	- for each (uncompressed) symbol, hcode contains the length
//	  of the corresponding code (in the compressed data)
//	- canonical codes are computed and stored in hcode
//	- the rules for constructing canonical codes are as follows:
//	  * shorter codes (if filled with zeroes to the right)
//	    have a numerically higher value than longer codes
//	  * for codes with the same length, numerical values
//	    increase with numerical symbol values
//	- because the canonical code table can be constructed from
//	  symbol lengths alone, the code table can be transmitted
//	  without sending the actual code values
//	- see http://www.compressconsult.com/huffman/
//

void
hufCanonicalCodeTable (Int64 hcode[HUF_ENCSIZE])
{
    Int64 n[59];

    //
    // For each i from 0 through 58, count the
    // number of different codes of length i, and
    // store the count in n[i].
    //

    for (int i = 0; i <= 58; ++i)
	n[i] = 0;

    for (int i = 0; i < HUF_ENCSIZE; ++i)
	n[hcode[i]] += 1;

    //
    // For each i from 58 through 1, compute the
    // numerically lowest code with length i, and
    // store that code in n[i].
    //

    Int64 c = 0;

    for (int i = 58; i > 0; --i)
    {
	Int64 nc = ((c + n[i]) >> 1);
	n[i] = c;
	c = nc;
    }

    //
    // hcode[i] contains the length, l, of the
    // code for symbol i.  Assign the next available
    // code of length l to the symbol and store both
    // l and the code in hcode[i].
    //

    for (int i = 0; i < HUF_ENCSIZE; ++i)
    {
	int l = hcode[i];

	if (l > 0)
	    hcode[i] = l | (n[l]++ << 6);
    }
}


//
// Compute Huffman codes (based on frq input) and store them in frq:
//	- code structure is : [63:lsb - 6:msb] | [5-0: bit length];
//	- max code length is 58 bits;
//	- codes outside the range [im-iM] have a null length (unused values);
//	- original frequencies are destroyed;
//	- encoding tables are used by hufEncode() and hufBuildDecTable();
//


struct FHeapCompare
{
    bool operator () (Int64 *a, Int64 *b) {return *a > *b;}
};


void
hufBuildEncTable
    (Int64*	frq,	// io: input frequencies [HUF_ENCSIZE], output table
     int*	im,	//  o: min frq index
     int*	iM)	//  o: max frq index
{
    //
    // This function assumes that when it is called, array frq
    // indicates the frequency of all possible symbols in the data
    // that are to be Huffman-encoded.  (frq[i] contains the number
    // of occurrences of symbol i in the data.)
    //
    // The loop below does three things:
    //
    // 1) Finds the minimum and maximum indices that point
    //    to non-zero entries in frq:
    //
    //     frq[im] != 0, and frq[i] == 0 for all i < im
    //     frq[iM] != 0, and frq[i] == 0 for all i > iM
    //
    // 2) Fills array fHeap with pointers to all non-zero
    //    entries in frq.
    //
    // 3) Initializes array hlink such that hlink[i] == i
    //    for all array entries.
    //

    AutoArray <int, HUF_ENCSIZE> hlink;
    AutoArray <Int64 *, HUF_ENCSIZE> fHeap;

    *im = 0;

    while (!frq[*im])
	(*im)++;

    int nf = 0;

    for (int i = *im; i < HUF_ENCSIZE; i++)
    {
	hlink[i] = i;

	if (frq[i])
	{
	    fHeap[nf] = &frq[i];
	    nf++;
	    *iM = i;
	}
    }

    //
    // Add a pseudo-symbol, with a frequency count of 1, to frq;
    // adjust the fHeap and hlink array accordingly.  Function
    // hufEncode() uses the pseudo-symbol for run-length encoding.
    //

    (*iM)++;
    frq[*iM] = 1;
    fHeap[nf] = &frq[*iM];
    nf++;

    //
    // Build an array, scode, such that scode[i] contains the number
    // of bits assigned to symbol i.  Conceptually this is done by
    // constructing a tree whose leaves are the symbols with non-zero
    // frequency:
    //
    //     Make a heap that contains all symbols with a non-zero frequency,
    //     with the least frequent symbol on top.
    //
    //     Repeat until only one symbol is left on the heap:
    //
    //         Take the two least frequent symbols off the top of the heap.
    //         Create a new node that has first two nodes as children, and
    //         whose frequency is the sum of the frequencies of the first
    //         two nodes.  Put the new node back into the heap.
    //
    // The last node left on the heap is the root of the tree.  For each
    // leaf node, the distance between the root and the leaf is the length
    // of the code for the corresponding symbol.
    //
    // The loop below doesn't actually build the tree; instead we compute
    // the distances of the leaves from the root on the fly.  When a new
    // node is added to the heap, then that node's descendants are linked
    // into a single linear list that starts at the new node, and the code
    // lengths of the descendants (that is, their distance from the root
    // of the tree) are incremented by one.
    //

    make_heap (&fHeap[0], &fHeap[nf], FHeapCompare());

    AutoArray <Int64, HUF_ENCSIZE> scode;
    memset (scode, 0, sizeof (Int64) * HUF_ENCSIZE);

    while (nf > 1)
    {
	//
	// Find the indices, mm and m, of the two smallest non-zero frq
	// values in fHeap, add the smallest frq to the second-smallest
	// frq, and remove the smallest frq value from fHeap.
	//

	int mm = fHeap[0] - frq;
	pop_heap (&fHeap[0], &fHeap[nf], FHeapCompare());
	--nf;

	int m = fHeap[0] - frq;
	pop_heap (&fHeap[0], &fHeap[nf], FHeapCompare());

	frq[m ] += frq[mm];
	push_heap (&fHeap[0], &fHeap[nf], FHeapCompare());

	//
	// The entries in scode are linked into lists with the
	// entries in hlink serving as "next" pointers and with
	// the end of a list marked by hlink[j] == j.
	//
	// Traverse the lists that start at scode[m] and scode[mm].
	// For each element visited, increment the length of the
	// corresponding code by one bit. (If we visit scode[j]
	// during the traversal, then the code for symbol j becomes
	// one bit longer.)
	//
	// Merge the lists that start at scode[m] and scode[mm]
	// into a single list that starts at scode[m].
	//
	
	//
	// Add a bit to all codes in the first list.
	//

	for (int j = m; true; j = hlink[j])
	{
	    scode[j]++;

	    assert (scode[j] <= 58);

	    if (hlink[j] == j)
	    {
		//
		// Merge the two lists.
		//

		hlink[j] = mm;
		break;
	    }
	}

	//
	// Add a bit to all codes in the second list
	//

	for (int j = mm; true; j = hlink[j])
	{
	    scode[j]++;

	    assert (scode[j] <= 58);

	    if (hlink[j] == j)
		break;
	}
    }

    //
    // Build a canonical Huffman code table, replacing the code
    // lengths in scode with (code, code length) pairs.  Copy the
    // code table from scode into frq.
    //

    hufCanonicalCodeTable (scode);
    memcpy (frq, scode, sizeof (Int64) * HUF_ENCSIZE);
}


//
// Pack an encoding table:
//	- only code lengths, not actual codes, are stored
//	- runs of zeroes are compressed as follows:
//
//	  unpacked		packed
//	  --------------------------------
//	  1 zero		0	(6 bits)
//	  2 zeroes		59
//	  3 zeroes		60
//	  4 zeroes		61
//	  5 zeroes		62
//	  n zeroes (6 or more)	63 n-6	(6 + 8 bits)
//

const int SHORT_ZEROCODE_RUN = 59;
const int LONG_ZEROCODE_RUN  = 63;
const int SHORTEST_LONG_RUN  = 2 + LONG_ZEROCODE_RUN - SHORT_ZEROCODE_RUN;
const int LONGEST_LONG_RUN   = 255 + SHORTEST_LONG_RUN;


void
hufPackEncTable
    (const Int64*	hcode,		// i : encoding table [HUF_ENCSIZE]
     int		im,		// i : min hcode index
     int		iM,		// i : max hcode index
     char**		pcode)		//  o: ptr to packed table (updated)
{
    char *p = *pcode;
    Int64 c = 0;
    int lc = 0;

    for (; im <= iM; im++)
    {
	int l = hufLength (hcode[im]);

	if (l == 0)
	{
	    int zerun = 1;

	    while ((im < iM) && (zerun < LONGEST_LONG_RUN))
	    {
		if (hufLength (hcode[im+1]) > 0 )	 
		    break;
		im++;
		zerun++;
	    }

	    if (zerun >= 2)
	    {
		if (zerun >= SHORTEST_LONG_RUN)
		{
		    outputBits (6, LONG_ZEROCODE_RUN, c, lc, p);
		    outputBits (8, zerun - SHORTEST_LONG_RUN, c, lc, p);
		}
		else
		{
		    outputBits (6, SHORT_ZEROCODE_RUN + zerun - 2, c, lc, p);
		}
		continue;
	    }
	}

	outputBits (6, l, c, lc, p);
    }

    if (lc > 0)
	*p++ = (unsigned char) (c << (8 - lc));

    *pcode = p;
}


//
// Unpack an encoding table packed by hufPackEncTable():
//

void
hufUnpackEncTable
    (const char**	pcode,		// io: ptr to packed table (updated)
     int		ni,		// i : input size (in bytes)
     int		im,		// i : min hcode index
     int		iM,		// i : max hcode index
     Int64*		hcode)		//  o: encoding table [HUF_ENCSIZE]
{
    memset (hcode, 0, sizeof (Int64) * HUF_ENCSIZE);

    const char *p = *pcode;
    Int64 c = 0;
    int lc = 0;

    for (; im <= iM; im++)
    {
	if (p - *pcode > ni)