Compaq ECQD2KCTE manual Longword, Quadword

Figure 2–2: Word Format

15 0

:A

A word is specified by its address, the address of the byte containing bit 0.

A word is a 16-bit value. The word is only supported in Alpha by the load, store, sign-extend, extract, mask, and insert instructions.

2.2.3 Longword

A longword is 4 contiguous bytes starting on an arbitrary byte boundary. The bits are num- bered from right to left, 0 through 31, as shown in Figure 2–3.

Figure 2–3: Longword Format

31 0

:A

A longword is specified by its address A, the address of the byte containing bit 0. A longword is a 32-bit value.

When interpreted arithmetically, a longword is a two’s-complement integer with bits of increasing significance from 0 through 30. Bit 31 is the sign bit. The longword is only sup- ported in Alpha by sign-extended load and store instructions and by longword arithmetic instructions.

Note:

Alpha implementations will impose a significant performance penalty when accessing longword operands that are not naturally aligned. (A naturally aligned longword has zero as the low-order two bits of its address.)

2.2.4 Quadword

A quadword is 8 contiguous bytes starting on an arbitrary byte boundary. The bits are num- bered from right to left, 0 through 63, as shown in Figure 2–4.

Figure 2–4: Quadword Format

63 0

:A

2–2Alpha Architecture Handbook