Appendix B
B-6 MIPS R4000 Microprocessor User's Manual
B.2 Instruction Notation Conventions
In this appendix, all variable subfields in an instruction format (such as fs,
ft, immediate, and so on) are shown in lower-case. The instruction name
(such as ADD, SUB, and so on) is shown in upper-case.
For the sake of clarity, we sometimes use an alias for a variable subfield in
the formats of specific instructions. For example, we use rs = base in the
format for load and store instructions. Such an alias is always lower case,
since it refers to a variable subfield.
In some instructions, the instruction subfields op and function can have
constant 6-bit values. When reference is made to these instructions,
upper-case mnemonics are used. For instance, in the floating-point ADD
instruction we use op = COP1 and function = ADD. In other cases, a single
field has both fixed and variable subfields, so the name contains both
upper and lower case characters. Bit encodings for mnemonics are shown
in Figure B-3 at the end of this appendix, and are also included with each
individual instruction.
In the instruction description examples that follow, the Operation section
describes the operation performed by each instruction using a high-level
language notation.
Instruction Notation Examples
The following examples illustrate the application of some of the
instruction notation conventions:
Example #1:
GPR[rt]
←
Sixteen zero bits are concatenated with an immediate
value (typically 16 bits), and the 32-bit string (with the lower
16 bits set to zero) is assigned to General Purpose Register
rt
.
Example #2:
Bit 15 (the sign bit) of an immediate value is extended for
16 bit positions, and the result is concatenated with bits 15
through 0 of the immediate value to form a 32-bit sign
extended value.
immediate || 0
16
(immediate
15
)
16
|| immediate
15...0
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