rle.c

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#include <stdio.h>
#include <grass/raster3d.h>

#define G_254_SQUARE 64516
#define G_254_TIMES_2 508

#define G_RLE_OUTPUT_CODE(code) (*((unsigned char *) dst++) = (code))
#define G_RLE_INPUT_CODE(codeP) (*(codeP) = *((unsigned char *) src++))

/*---------------------------------------------------------------------------*/

static int G_rle_codeLength(int length)
{
    register int lPrime;
    int codeLength;

    if (length == -1)
        return 2;
    if (length < 254)
        return 1;
    if (length < G_254_TIMES_2)
        return 2;
    if (length < G_254_SQUARE)
        return 3;

    codeLength = 0;
    lPrime = length;
    while ((lPrime = lPrime / 254) != 0)
        codeLength++;
    return codeLength + 2;
}

/*---------------------------------------------------------------------------*/

static char *rle_length2code(int length, char *dst)
{
    register int lPrime;

    if (length == -1) {         /* stop code */
        G_RLE_OUTPUT_CODE(255);
        G_RLE_OUTPUT_CODE(255);

        return dst;
    }

    if (length < 254) {
        G_RLE_OUTPUT_CODE(length);

        return dst;
    }

    if (length < G_254_TIMES_2) {       /* length == 254 + a; a < 254 */
        G_RLE_OUTPUT_CODE(255);
        G_RLE_OUTPUT_CODE(length % 254);

        return dst;
    }

    if (length < G_254_SQUARE) {        /* length = 254 * b + a; b, a < 254 */
        G_RLE_OUTPUT_CODE(254); /* this if-clause included for efficiency only */
        G_RLE_OUTPUT_CODE(length / 254);
        G_RLE_OUTPUT_CODE(length % 254);

        return dst;
    }

    /* TODO implement a corrected version for larger strings */
    /* This code is simply wrong, it works only for c == 2, critical number for wrong computation is 254*254*2 = 129032 */
    /* CORRECT: length = 254 ^ 2 + 254 * b + a; b, a < 254 */

    /* WRONG: length = 254 ^ c + 254 * b + a; b, a < 254 */

    lPrime = length;
    while ((lPrime = lPrime / 254) != 0)
        G_RLE_OUTPUT_CODE(254);

    length %= G_254_SQUARE;

    G_RLE_OUTPUT_CODE(length / 254);
    G_RLE_OUTPUT_CODE(length % 254);

    /* Next should be: length = 254 ^ 3 + 254 ^ 2 * c + 254 * b + a; c, b, a < 254 */

    return dst;
}

/*---------------------------------------------------------------------------*/

static char *rle_code2length(char *src, int *length)
{
    int code;

    if (G_RLE_INPUT_CODE(length) < 254)
        return src;             /* length < 254 */

    if (*length == 255) {       /* length == 254 + a; a < 254 */
        if (G_RLE_INPUT_CODE(length) == 255) {
            *length = -1;
            return src;
        }

        *length += 254;
        return src;
    }

    G_RLE_INPUT_CODE(&code);
    if (code < 254) {           /* length = 254 * b + a; b, a < 254 */
        G_RLE_INPUT_CODE(length);       /* this if-clause included for efficiency only */
        *length += 254 * code;

        return src;
    }

    /* TODO implement a corrected version for larger strings */
    /* This code is simply wrong, it works only for c == 2, critical number for wrong computation is 254*254*2 = 129032 */
    /* CORRECT: length = 254 ^ 2 + 254 * b + a; b, a < 254 */

    /* WRONG: length = 254 ^ c + 254 * b + a; b, a < 254 */

    *length = G_254_SQUARE;
    while (G_RLE_INPUT_CODE(&code) == 254)
        *length *= 254;

    *length += 254 * code;
    G_RLE_INPUT_CODE(&code);
    *length += code;

    /* Next should be: length = 254 ^ 3 + 254 ^ 2 * c + 254 * b + a; c, b, a < 254 */

    return src;
}

/*---------------------------------------------------------------------------*/

int Rast3d_rle_count_only(char *src, int nofElts, int eltLength)
{
    int length, nofEqual;
    char *head, *tail, *headStop, *headStop2;

    if (nofElts <= 0)
        Rast3d_fatal_error("trying to encode 0-length list");

    length = 0;
    nofEqual = 1;
    head = src + eltLength;
    tail = src;

    headStop = src + nofElts * eltLength;

    while (head != headStop) {
        headStop2 = head + eltLength;

        while (head != headStop2) {
            if (*head != *tail) {
                length += G_rle_codeLength(nofEqual) + eltLength;
                nofEqual = 1;
                tail = headStop2 - eltLength;
                break;
            }
            head++;
            tail++;
        }

        if (head == headStop2) {
            nofEqual++;
            continue;
        }

        head = headStop2;
    }
    length += G_rle_codeLength(nofEqual) + eltLength;

    return length + G_rle_codeLength(-1);
}

/*---------------------------------------------------------------------------*/

void Rast3d_rle_encode(char *src, char *dst, int nofElts, int eltLength)
{
    int length, nofEqual;
    char *head, *tail, *headStop, *headStop2;

    if (nofElts <= 0)
        Rast3d_fatal_error("trying to encode 0-length list");

    length = 0;
    nofEqual = 1;
    head = src + eltLength;
    tail = src;

    headStop = src + nofElts * eltLength;

    while (head != headStop) {
        headStop2 = head + eltLength;

        while (head != headStop2) {
            if (*head != *tail) {
                dst = rle_length2code(nofEqual, dst);
                tail = headStop2 - eltLength * (nofEqual + 1);
                head = tail + eltLength;
                /*      printf ("equal %d char %d\n", nofEqual, *tail); */
                while (tail != head)
                    *dst++ = *tail++;
                length += G_rle_codeLength(nofEqual) + eltLength;
                nofEqual = 1;
                tail = headStop2 - eltLength;
                break;
            }
            head++;
            tail++;
        }

        if (head == headStop2) {
            nofEqual++;
            continue;
        }

        head = headStop2;
    }

    dst = rle_length2code(nofEqual, dst);
    tail = headStop - eltLength * nofEqual;
    head = tail + eltLength;
    while (tail != head)
        *dst++ = *tail++;
    length += G_rle_codeLength(nofEqual) + eltLength;
    dst = rle_length2code(-1, dst);
    length += G_rle_codeLength(-1);
    rle_code2length(dst - 2, &nofEqual);
}

/*---------------------------------------------------------------------------*/

void
Rast3d_rle_decode(char *src, char *dst, int nofElts, int eltLength,
             int *lengthEncode, int *lengthDecode)
{
    int nofEqual;
    char *src2, *srcStop, *src2Stop, *dstFirst;

    srcStop = src + nofElts * eltLength;
    dstFirst = dst;

    while (src != srcStop) {
        src = rle_code2length(src, &nofEqual);

        if (nofEqual == -1) {
            *lengthEncode = src - (srcStop - nofElts * eltLength);
            *lengthDecode = dst - dstFirst;
            return;
        }

        while (nofEqual--) {
            src2 = src;
            src2Stop = src2 + eltLength;
            while (src2 != src2Stop)
                *dst++ = *src2++;
        }
        src += eltLength;
    }

    Rast3d_fatal_error("Rast3d_rle_decode: string ends prematurely");
}

/*---------------------------------------------------------------------------*/

/* TODO: Find out if this function used at all.
 * Seems to be some leftover from the early pre-SVN days of GRASS GIS.
 * Maris, 2018.
 */
void test_rle()
{
    char c[100];
    int length;

    do {
        printf("length? ");
        if (scanf("%d", &length) != 1)
        Rast3d_fatal_error("Error reading length");
        printf("length = %d\n", length);
        printf("codeLength %d   ", G_rle_codeLength(length));
        (void)rle_length2code(length, c);
        length = 0;
        (void)rle_code2length(c, &length);
        printf("output length %d\n\n", length);
    } while (1);
}