- if (exif_data[0] != 0x45 || exif_data[1] != 0x78
- || exif_data[2] != 0x69 || exif_data[3] != 0x66
- || exif_data[4] != 0 || exif_data[5] != 0)
- return -1;
-
- /* Read Exif body */
- length = length > exif_data.length ? exif_data.length : length;
- for (int i = 0; i < length; i++)
- exif_data[i] = in.read();
-
- if (length < 12)
- return -1; /* Length of an IFD entry */
-
- /* Discover byte order */
- if (exif_data[0] == 0x49 && exif_data[1] == 0x49)
- is_motorola = 0;
- else if (exif_data[0] == 0x4D && exif_data[1] == 0x4D)
- is_motorola = 1;
- else
- return -1;
-
- /* Check Tag Mark */
- if (is_motorola == 1) {
- if (exif_data[2] != 0)
- return -1;
- if (exif_data[3] != 0x2A)
- return -1;
- } else {
- if (exif_data[3] != 0)
- return -1;
- if (exif_data[2] != 0x2A)
- return -1;
- }
-
- /* Get first IFD offset (offset to IFD0) */
- int offset;
- if (is_motorola == 1) {
- if (exif_data[4] != 0)
- return -1;
- if (exif_data[5] != 0)
- return -1;
- offset = exif_data[6];
- offset <<= 8;
- offset += exif_data[7];
- } else {
- if (exif_data[7] != 0)
- return -1;
- if (exif_data[6] != 0)
- return -1;
- offset = exif_data[5];
- offset <<= 8;
- offset += exif_data[4];
- }
- if (offset > length - 2)
- return -1; /* check end of data segment */
-
- /* Get the number of directory entries contained in this IFD */
- int number_of_tags;
- if (is_motorola == 1) {
- number_of_tags = exif_data[offset];
- number_of_tags <<= 8;
- number_of_tags += exif_data[offset + 1];
- } else {
- number_of_tags = exif_data[offset + 1];
- number_of_tags <<= 8;
- number_of_tags += exif_data[offset];
- }
- if (number_of_tags == 0)
- return -1;
- offset += 2;
-
- /* Search for Orientation Tag in IFD0 */
- for (;;) {
- if (offset > length - 12)
- return -1; /* check end of data segment */
- /* Get Tag number */
- int tagnum;
- if (is_motorola == 1) {
- tagnum = exif_data[offset];
- tagnum <<= 8;
- tagnum += exif_data[offset + 1];
- } else {
- tagnum = exif_data[offset + 1];
- tagnum <<= 8;
- tagnum += exif_data[offset];
- }
- if (tagnum == 0x0112)
- break; /* found Orientation Tag */
- if (--number_of_tags == 0)
- return -1;
- offset += 12;
- }
-
- /* Get the Orientation value */
- if (is_motorola == 1) {
- if (exif_data[offset + 8] != 0)
- return -1;
- set_flag = exif_data[offset + 9];
- } else {
- if (exif_data[offset + 9] != 0)
- return -1;
- set_flag = exif_data[offset + 8];
- }
- if (set_flag > 8)
- return -1;