 int mif_validate(jas_stream_t *in)
 {
	jas_uchar buf[MIF_MAGICLEN];
 	uint_fast32_t magic;
 	int i;
 	int n;

	assert(JAS_STREAM_MAXPUTBACK >= MIF_MAGICLEN);

	/* Read the validation data (i.e., the data used for detecting
	  the format). */
	if ((n = jas_stream_read(in, buf, MIF_MAGICLEN)) < 0) {
		return -1;
	}

	/* Put the validation data back onto the stream, so that the
	  stream position will not be changed. */
	for (i = n - 1; i >= 0; --i) {
		if (jas_stream_ungetc(in, buf[i]) == EOF) {
			return -1;
		}
	}

	/* Was enough data read? */
	if (n < MIF_MAGICLEN) {
		return -1;
	}

	/* Compute the signature value. */
	magic = (JAS_CAST(uint_fast32_t, buf[0]) << 24) |
	  (JAS_CAST(uint_fast32_t, buf[1]) << 16) |
	  (JAS_CAST(uint_fast32_t, buf[2]) << 8) |
	  buf[3];

	/* Ensure that the signature is correct for this format. */
	if (magic != MIF_MAGIC) {
		return -1;
	}

	return 0;
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.