src/pack.c


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#include <stdio.h>

int frombigendian(const unsigned char in[4])
{
    return (in[0] << 24) | (in[1] << 16) | (in[2] << 8) | in[3];
}

void tobigendian(const int in, unsigned char out[4])
{
    out[0] = (in >> 24) & 0xff;
    out[1] = (in >> 16) & 0xff;
    out[2] = (in >> 8) & 0xff;
    out[3] = in & 0xff;
}

/* function is lifted from */
/* https://github.com/heinrich5991/libtw2/blob/b9286674da94d3d45b9c10ffce517af394e2d58c/packer/src/lib.rs#L62 */
int readint(char **cp)
{
    int result = 0;
    int len = 1;

    unsigned char src = **cp;
    (*cp)++;

    int sign = ((src >> 6) & 1);
    result |= (src & 0b00111111);

    for (int i = 0; i < 4; i++)
    {
        // printf("(%d, ", src);
        if ((src & 0b10000000) == 0)
            break;

        src = **cp;
        (*cp)++;

        len++;

        if (i == 3 && (src & 0b11110000) != 0)
            printf("[ WARNING ] Non zero int padding!\n");

        result |= (src & 0b01111111) << (6 + 7 * i);
    }
    if (len > 1 && src == 0b00000000)
        printf("[ WARNING ] Overlong int encoding!\n");

    result ^= -sign;

    return result;
}

/*
int readint(char **src)
{
    const int sign = (**src >> 6) & 1;

    int out = **src & 0x3f;

    const static int masks[] = {0x7F, 0x7F, 0x7F, 0x0F};
    const static int shifts[] = {6, 6 + 7, 6 + 7 + 7, 6 + 7 + 7 + 7};

    for (unsigned int i = 0; i < sizeof(masks); i++)
    {
        if (!(**src & 0x80))
            break;
        (*src)++;
        out |= (**src & masks[i]) << shifts[i];
    }
    (*src)++;
    out ^= -sign;
    return out;
}
*/

/* function is lifted from */
/* https://github.com/heinrich5991/libtw2/blob/b9286674da94d3d45b9c10ffce517af394e2d58c/packer/src/lib.rs#L105 */
void writeint(int i, char **cp)
{
    int sign = i < 0;
    unsigned int in = i;
    in = (in ^ -sign);
    char next = (in & 0b00111111);
    in >>= 6;

    char head = 0;
    if (in != 0)
        head |= 0b10000000;
    if (sign != 0)
        head |= 0b01000000;

    **cp = head | next;
    (*cp)++;

    while (in != 0)
    {
        next = (in & 0b01111111);
        in >>= 7;

        if (in != 0)
            head = 0b10000000;
        else
            head = 0;

        **cp = head | next;
        (*cp)++;
    }
}