static int g2m_load_cursor(AVCodecContext *avctx, G2MContext *c,
                           GetByteContext *gb)
{
    int i, j, k;
    uint8_t *dst;
    uint32_t bits;
    uint32_t cur_size, cursor_w, cursor_h, cursor_stride;
    uint32_t cursor_hot_x, cursor_hot_y;
    int cursor_fmt;
    uint8_t *tmp;

    cur_size      = bytestream2_get_be32(gb);
    cursor_w      = bytestream2_get_byte(gb);
    cursor_h      = bytestream2_get_byte(gb);
    cursor_hot_x  = bytestream2_get_byte(gb);
    cursor_hot_y  = bytestream2_get_byte(gb);
    cursor_fmt    = bytestream2_get_byte(gb);

    cursor_stride = cursor_w * 4;

    if (cursor_w < 1 || cursor_w > 256 ||
        cursor_h < 1 || cursor_h > 256) {
        av_log(avctx, AV_LOG_ERROR, "Invalid cursor dimensions %dx%d\n",
               cursor_w, cursor_h);
        return AVERROR_INVALIDDATA;
    }
    if (cursor_hot_x > cursor_w || cursor_hot_y > cursor_h) {
        av_log(avctx, AV_LOG_WARNING, "Invalid hotspot position %d,%d\n",
               cursor_hot_x, cursor_hot_y);
        cursor_hot_x = FFMIN(cursor_hot_x, cursor_w - 1);
        cursor_hot_y = FFMIN(cursor_hot_y, cursor_h - 1);
    }
    if (cur_size - 9 > bytestream2_get_bytes_left(gb) ||
        c->cursor_w * c->cursor_h / 4 > cur_size) {
        av_log(avctx, AV_LOG_ERROR, "Invalid cursor data size %d/%d\n",
               cur_size, bytestream2_get_bytes_left(gb));
        return AVERROR_INVALIDDATA;
    }
    if (cursor_fmt != 1 && cursor_fmt != 32) {
        avpriv_report_missing_feature(avctx, "Cursor format %d",
                                      cursor_fmt);
        return AVERROR_PATCHWELCOME;
    }

    if (cursor_fmt == 1 && cursor_w % 32) {
        avpriv_report_missing_feature(avctx, "odd monochrome cursor width %d", cursor_w);
        return AVERROR_PATCHWELCOME;
    }

    tmp = av_realloc(c->cursor, cursor_stride * cursor_h);
    if (!tmp) {
        av_log(avctx, AV_LOG_ERROR, "Cannot allocate cursor buffer\n");
        return AVERROR(ENOMEM);
    }

    c->cursor        = tmp;
    c->cursor_w      = cursor_w;
    c->cursor_h      = cursor_h;
    c->cursor_hot_x  = cursor_hot_x;
    c->cursor_hot_y  = cursor_hot_y;
    c->cursor_fmt    = cursor_fmt;
    c->cursor_stride = cursor_stride;

    dst = c->cursor;
    switch (c->cursor_fmt) {
    case 1: // old monochrome
        for (j = 0; j < c->cursor_h; j++) {
            for (i = 0; i < c->cursor_w; i += 32) {
                bits = bytestream2_get_be32(gb);
                for (k = 0; k < 32; k++) {
                    dst[0] = !!(bits & 0x80000000);
                    dst += 4;
                    bits <<= 1;
                }
            }
        }

        dst = c->cursor;
        for (j = 0; j < c->cursor_h; j++) {
            for (i = 0; i < c->cursor_w; i += 32) {
                bits = bytestream2_get_be32(gb);
                for (k = 0; k < 32; k++) {
                    int mask_bit = !!(bits & 0x80000000);
                    switch (dst[0] * 2 + mask_bit) {
                    case 0:
                        dst[0] = 0xFF; dst[1] = 0x00;
                        dst[2] = 0x00; dst[3] = 0x00;
                        break;
                    case 1:
                        dst[0] = 0xFF; dst[1] = 0xFF;
                        dst[2] = 0xFF; dst[3] = 0xFF;
                        break;
                    default:
                        dst[0] = 0x00; dst[1] = 0x00;
                        dst[2] = 0x00; dst[3] = 0x00;
                    }
                    dst += 4;
                    bits <<= 1;
                }
            }
        }
        break;
    case 32: // full colour
        /* skip monochrome version of the cursor and decode RGBA instead */
        bytestream2_skip(gb, c->cursor_h * (FFALIGN(c->cursor_w, 32) >> 3));
        for (j = 0; j < c->cursor_h; j++) {
            for (i = 0; i < c->cursor_w; i++) {
                int val = bytestream2_get_be32(gb);
                *dst++ = val >>  0;
                *dst++ = val >>  8;
                *dst++ = val >> 16;
                *dst++ = val >> 24;
            }
        }
        break;
    default:
        return AVERROR_PATCHWELCOME;
    }
    return 0;
}