Compaq ECQD2KCTE manual Instruction Set Characteristics, Terminology and Conventions

Floating-Point Operate Instructions

The floating-point operate instructions include four complete sets of VAX and IEEE arith- metic instructions, plus instructions for performing conversions between floating-point and integer quantities.

In addition to the operations found in conventional RISC architectures, Alpha includes condi- tional move instructions for avoiding branches and merge sign/exponent instructions for simple field manipulation.

The arithmetic trap enables and rounding mode are encoded in the function field of each in stru cti on , rath er t han kep t i n g lo bal stat e bi ts . Th at mak es i t eas ier to pi pel in e implementations.

1.5 Instruction Set Characteristics

Alpha instruction set characteristics are as follows:

•All instructions are 32 bits long and have a regular format.

•There are 32 integer registers (R0 through R31), each 64 bits wide. R31 reads as zero, and writes to R31 are ignored.

•All integer data manipulation is between integer registers, with up to two variable regis- ter source operands (one may be an 8-bit literal) and one register destination operand.

•There are 32 floating-point registers (F0 through F31), each 64 bits wide. F31 reads as zero, and writes to F31 are ignored.

•All floating-point data manipulation is between floating-point registers, with up to two register source operands and one register destination operand.

•Instructions can move data in an integer register file to a floating-point register file, and data in a floating-point register file to an integer register file. The instructions do not interpret bits in the register files and do not access memory.

•All memory reference instructions are of the load/store type that moves data between registers and memory.

•There are no branch condition codes. Branch instructions test an integer or floating- point register value, which may be the result of a previous compare.

•Integer and logical instructions operate on quadwords.

•Floating-point instructions operate on G_floating, F_floating, and IEEE extended, dou- ble, and single operands. D_floating "format compatibility," in which binary files of D_floating numbers may be processed, but without the last 3 bits of fraction precision, is also provided.

•A minimal number of VAX compatibility instructions are included.

1.6Terminology and Conventions

The following sections describe the terminology and conventions used in this book.

1–6Alpha Architecture Handbook