FPU BCD (Binary-Coded Decimal)

One other feature of the FPU that can be taken advantage of is the BCD capability. BCD can be loaded, calculations performed, and data written back out. It allows for 18 4-bit BCD digits plus a sign bit within a number to be processed simultaneously . Due to precision loss, a number represented by BCD and utilizing BCD math is the safest method of representing monetary values (money) without losing pennies. This will be discussed in Chapter 15, "Binary-Coded Decimal."

Figure 8-4: Ten-byte BCD data storage. The MSB in the far left byte (byte #9) is the sign bit and the rightmost eight bytes (#8...0) contain the BCD value pairs. The 18 ^th BCD digit resides in the upper nibble of byte #8 and the first BCD digit resides in the lower nibble of byte #0.

FBLD FPU (BCD Load)

Mnemonic

P

PII

K6

3D!

3Mx+

SSE

SSE2

A64

SSE3

E64T

FBLD