Compaq ECQD2KCTE manual Quadword Integer Format in Floating-Point Unit

Note:

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

2.2.8 Quadword Integer Format in Floating-Point Unit

A quadword integer operand occupies 64 bits in memory, arranged as shown in Figure 2–21.

Figure 2–21: Quadword Integer Datum

31 30 0

S

Integer Lo	:A
Integer Hi	:A+4

A quadword integer operand occupies 64 bits in a floating register, arranged as shown in Fig- ure 2–22.

Figure 2–22: Quadword Integer Floating-Register Format

63 62 32 31 0

S

Integer Hi

Integer Lo

:Fx

There is no explicit quadword load or store instruction; the T_floating load/store instructions are used to move quadword data between memory and the floating registers. (The ITOFT and FTOIT are used to move quadword data between integer and floating registers.)

The T_floating load instruction performs no bit reordering on input. The T_floating store instruction performs no bit reordering on output. This instruction does no checking of the data; when used to store quadwords, the preceding operation should have specified a quadword result.

Note:

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

2.2.9Data Types with No Hardware Support

•The following VAX data types are not directly supported in Alpha hardware. Octaword

•H_floating

•D_floating (except load/store and convert to/from G_floating)

•Variable-Length Bit Field

•Character String

2–12Alpha Architecture Handbook