Function BmpRead4Rle

src/bmp.cpp:71–140

* Reads a 4-bit RLE compressed bitmap * The bitmap is converted to a 8 bpp bitmap */

 * The bitmap is converted to a 8 bpp bitmap
 */
static inline bool BmpRead4Rle(RandomAccessFile &file, BmpInfo &info, BmpData &data)
{
	uint x = 0;
	uint y = info.height - 1;
	uint8_t *pixel = &data.bitmap[y * static_cast<size_t>(info.width)];
	while (y != 0 || x < info.width) {
		if (file.AtEndOfFile()) return false; // the file is shorter than expected

		uint8_t n = file.ReadByte();
		uint8_t c = file.ReadByte();
		if (n == 0) {
			switch (c) {
				case 0: // end of line
					x = 0;
					if (y == 0) return false;
					pixel = &data.bitmap[--y * static_cast<size_t>(info.width)];
					break;

				case 1: // end of bitmap
					return true;

				case 2: { // delta
					if (file.AtEndOfFile()) return false;
					uint8_t dx = file.ReadByte();
					uint8_t dy = file.ReadByte();

					/* Check for over- and underflow. */
					if (x + dx >= info.width || x + dx < x || dy > y) return false;

					x += dx;
					y -= dy;
					pixel = &data.bitmap[y * info.width + x];
					break;
				}

				default: { // uncompressed
					uint i = 0;
					while (i++ < c) {
						if (file.AtEndOfFile() || x >= info.width) return false;
						uint8_t b = file.ReadByte();
						*pixel++ = GB(b, 4, 4);
						x++;
						if (i++ < c) {
							if (x >= info.width) return false;
							*pixel++ = GB(b, 0, 4);
							x++;
						}
					}
					/* Padding for 16 bit align */
					file.SkipBytes(((c + 1) / 2) % 2);
					break;
				}
			}
		} else {
			/* Apparently it is common to encounter BMPs where the count of
			 * pixels to be written is higher than the remaining line width.
			 * Ignore the superfluous pixels instead of reporting an error. */
			uint i = 0;