static void qtrle_decode_8bpp(QtrleContext *s) { int stream_ptr; int header; int start_line; int lines_to_change; signed char rle_code; int row_ptr, pixel_ptr; int row_inc = s->frame.linesize[0]; unsigned char pi1, pi2, pi3, pi4; /* 4 palette indices */ unsigned char *rgb = s->frame.data[0]; int pixel_limit = s->frame.linesize[0] * s->avctx->height; /* check if this frame is even supposed to change */ if (s->size < 8) return; /* start after the chunk size */ stream_ptr = 4; /* fetch the header */ CHECK_STREAM_PTR(2); header = BE_16(&s->buf[stream_ptr]); stream_ptr += 2; /* if a header is present, fetch additional decoding parameters */ if (header & 0x0008) { CHECK_STREAM_PTR(8); start_line = BE_16(&s->buf[stream_ptr]); stream_ptr += 4; lines_to_change = BE_16(&s->buf[stream_ptr]); stream_ptr += 4; } else { start_line = 0; lines_to_change = s->avctx->height; } row_ptr = row_inc * start_line; while (lines_to_change--) { CHECK_STREAM_PTR(2); pixel_ptr = row_ptr + (4 * (s->buf[stream_ptr++] - 1)); while ((rle_code = (signed char)s->buf[stream_ptr++]) != -1) { if (rle_code == 0) { /* there's another skip code in the stream */ CHECK_STREAM_PTR(1); pixel_ptr += (4 * (s->buf[stream_ptr++] - 1)); } else if (rle_code < 0) { /* decode the run length code */ rle_code = -rle_code; /* get the next 4 bytes from the stream, treat them as palette * indices, and output them rle_code times */ CHECK_STREAM_PTR(4); pi1 = s->buf[stream_ptr++]; pi2 = s->buf[stream_ptr++]; pi3 = s->buf[stream_ptr++]; pi4 = s->buf[stream_ptr++]; CHECK_PIXEL_PTR(rle_code * 4); while (rle_code--) { rgb[pixel_ptr++] = pi1; rgb[pixel_ptr++] = pi2; rgb[pixel_ptr++] = pi3; rgb[pixel_ptr++] = pi4; } } else { /* copy the same pixel directly to output 4 times */ rle_code *= 4; CHECK_STREAM_PTR(rle_code); CHECK_PIXEL_PTR(rle_code); while (rle_code--) { rgb[pixel_ptr++] = s->buf[stream_ptr++]; } } } row_ptr += row_inc; } }