Byte Swapping

Microsoft Excel BIFF files are transportable across the MS-DOS/Windows (Intel 80x86) and Apple Macintosh (Motorola 680x0) operating systems, among others. To support transportability, Microsoft Excel writes BIFF files in the 80x86 format, where the low-order byte of the word appears first in the file, followed by the high-order byte.

Whenever Microsoft Excel for the Macintosh reads or writes a BIFF file, it calls a function that swaps the high- and low-order bytes of every 16-bit word in every record in the file. For 32-bit longs, the bytes in each 16-bit word are swapped first, and then the two 16-bit words are swapped. Be sure to include a byte-swap function in any custom BIFF utility you write for the Macintosh.