jpegutil.c

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/*
 * jpegutil.c --
 *
 * Various utility routines used in the jpeg encoder/decoder.  Large parts
 * are stolen from the IJG code
 */
/*
 * $Id: jpegutil.c,v 1.4 2004/08/18 21:38:43 enlf Exp $
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "jpeg.h"
#include "mcu.h"
#include "proto.h"

/*
 * To fix memory leaks, memory is allocated once for the mcu buffers.
 * Enough memory is reserved to accomodate up to 1024-wide images
 * with up to 4 components.
 */
static char mcuROW1Memory[1024 * sizeof(MCU)];
static char mcuROW2Memory[1024 * sizeof(MCU)];
static char buf1Memory[1024 * 4 * sizeof(ComponentType)];
static char buf2Memory[1024 * 4 * sizeof(ComponentType)];


unsigned int bitMask[] = {  0xffffffff, 0x7fffffff, 0x3fffffff, 0x1fffffff,
                            0x0fffffff, 0x07ffffff, 0x03ffffff, 0x01ffffff,
                            0x00ffffff, 0x007fffff, 0x003fffff, 0x001fffff,
                            0x000fffff, 0x0007ffff, 0x0003ffff, 0x0001ffff,
                            0x0000ffff, 0x00007fff, 0x00003fff, 0x00001fff,
                            0x00000fff, 0x000007ff, 0x000003ff, 0x000001ff,
                            0x000000ff, 0x0000007f, 0x0000003f, 0x0000001f,
                            0x0000000f, 0x00000007, 0x00000003, 0x00000001};
/*
 *--------------------------------------------------------------
 *
 * JroundUp --
 *
 *        Compute a rounded up to next multiple of b; a >= 0, b > 0 
 *
 * Results:
 *        Rounded up value.
 *
 * Side effects:
 *        None.
 *
 *--------------------------------------------------------------
 */
int JroundUp (int a, int b)
{
    a += b - 1;
    return a - (a % b);
}

/*
 *--------------------------------------------------------------
 *
 * DecoderStructInit --
 *
 *        Initalize the rest of the fields in the decompression
 *        structure.
 *
 * Results:
 *        None.
 *
 * Side effects:
 *        None.
 *
 *--------------------------------------------------------------
 */

void DecoderStructInit (DecompressInfo *dcPtr)
{
    char *buf1,*buf2;
    short ci,i;
    JpegComponentInfo *compPtr;
    int mcuSize;

    /*
     * Check sampling factor validity.
     */
    for (ci = 0; ci < dcPtr->numComponents; ci++) {
        compPtr = &dcPtr->compInfo[ci];
        if ((compPtr->hSampFactor != 1) || (compPtr->vSampFactor != 1)) {
           fprintf (stderr, "Error: Downsampling is not supported.\n");
           /* exit(-1); */
           dcPtr->error = -1; return; 
        }
    }

    /*
     * Prepare array describing MCU composition
     */
    if (dcPtr->compsInScan == 1) {
        dcPtr->MCUmembership[0] = 0;
    } else {
        short ci;

        if (dcPtr->compsInScan > 4) {
            fprintf (stderr, "Too many components for interleaved scan\n");
            /* exit (1); */
            dcPtr->error = -1; return;
        }

        for (ci = 0; ci < dcPtr->compsInScan; ci++) {
            dcPtr->MCUmembership[ci] = ci;
        }
    }

    /*
     * Initialize mucROW1 and mcuROW2 which buffer two rows of
     * pixels for predictor calculation.
     */

    mcuROW1 = (MCU *) mcuROW1Memory;
    mcuROW2 = (MCU *) mcuROW2Memory;

    mcuSize=dcPtr->compsInScan * sizeof(ComponentType);

    buf1 = buf1Memory;
    buf2 = buf2Memory;

    for (i=0;i<dcPtr->imageWidth;i++) {
        mcuROW1[i]=(MCU)(buf1+i*mcuSize);
        mcuROW2[i]=(MCU)(buf2+i*mcuSize);
    }

    dcPtr->error = 0;

}/*endof DecoderStructInit*/


/*
 *--------------------------------------------------------------
 *
 * FixHuffTbl --
 *
 *      Compute derived values for a Huffman table one the DHT marker
 *      has been processed.  This generates both the encoding and
 *      decoding tables.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      None.
 *
 *--------------------------------------------------------------
 */
void FixHuffTbl (HuffmanTable *htbl)
{
    int p, i, l, lastp, si;
    char huffsize[257];
    Ushort huffcode[257];
    Ushort code;
    int size;
    int value, ll, ul;

    /*
     * Figure C.1: make table of Huffman code length for each symbol
     * Note that this is in code-length order.
     */
    p = 0;
    for (l = 1; l <= 16; l++) {
        for (i = 1; i <= (int)htbl->bits[l]; i++)
            huffsize[p++] = (char)l;
    }
    huffsize[p] = 0;
    lastp = p;


    /*
     * Figure C.2: generate the codes themselves
     * Note that this is in code-length order.
     */
    code = 0;
    si = huffsize[0];
    p = 0;
    while (huffsize[p]) {
        while (((int)huffsize[p]) == si) {
            huffcode[p++] = code;
            code++;
        }
        code <<= 1;
        si++;
    }

    /*
     * Figure C.3: generate encoding tables
     * These are code and size indexed by symbol value
     * Set any codeless symbols to have code length 0; this allows
     * EmitBits to detect any attempt to emit such symbols.
     */
    MEMSET(htbl->ehufsi, 0, sizeof(htbl->ehufsi));

    for (p = 0; p < lastp; p++) {
        htbl->ehufco[htbl->huffval[p]] = huffcode[p];
        htbl->ehufsi[htbl->huffval[p]] = huffsize[p];
    }

    /*
     * Figure F.15: generate decoding tables
     */
    p = 0;
    for (l = 1; l <= 16; l++) {
        if (htbl->bits[l]) {
            htbl->valptr[l] = p;
            htbl->mincode[l] = huffcode[p];
            p += htbl->bits[l];
            htbl->maxcode[l] = huffcode[p - 1];
        } else {
            htbl->maxcode[l] = -1;
        }
    }

    /*
     * We put in this value to ensure HuffDecode terminates.
     */
    htbl->maxcode[17] = 0xFFFFFL;

    /*
     * Build the numbits, value lookup tables.
     * These table allow us to gather 8 bits from the bits stream,
     * and immediately lookup the size and value of the huffman codes.
     * If size is zero, it means that more than 8 bits are in the huffman
     * code (this happens about 3-4% of the time).
     */
    /*bzero (htbl->numbits, sizeof(htbl->numbits));*/
    memset(htbl->numbits, 0, sizeof(htbl->numbits));

    for (p=0; p<lastp; p++) {
        size = huffsize[p];
        if (size <= 8) {
            value = htbl->huffval[p];
            code = huffcode[p];
            ll = code << (8-size);
            if (size < 8) {
                ul = ll | bitMask[24+size];
            } else {
                ul = ll;
            }
            for (i=ll; i<=ul; i++) {
                htbl->numbits[i] = size;
                htbl->value[i] = value;
            }
        }
    }
}