FPU Data Types ..
The FPU_Stack Registers are all, and always, 80 Bits wide, and all data, in an FPU Register is always an 80 Bits Extended Precision Number.
Nevertheless the FPU can read and write various other Formats, from and to Memory. These Memory Data may be either Reals or 16 Bits, 32 Bits, 64 Bits Integers, or Binary Coded Decimal 80 Bits Records . At a size point of view, these Formats, are:
Single Precision Format (32 Bits):
31 23 15 7 0
__| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __|
Double Precision Format (64 Bits ):
63 52 7 0
__| __| __| __| ..... __| __| __| __| __| __| __| __| __| __| __| __| __| __| .......... __| __| __| __| __| __| __| __| __| __| __|
Extended Precision Format (80 Bits), the 'true' FPU regs Format:
79 64 7 0
__| __| __| __| ..... __| __| __| __| __| __| __| __| __| __| __| __| __| __| .......... __| __| __| __| __| __| __| __| __| __| __|
Packed Decimal Integer (BCD) (80 Bits ):
79 72 68 64 7 4 0
__| __| __| __| __| __| __| __| __| __| __| __| __| __| __| __ .......... __| __| __| __| __| __| __| __| __| __| __| __| __| __|
Sign Unused D17 D16 D15 D2 D1 D0
~~~~~~~