THE MICROARCHITECTURE LEVEL - Structured Computer Organization - page 262

4.2.3 The IJVM Instruction Set

The IJVM instruction set is shown in Fig. 4-11. Each instruction consists of an
opcode and sometimes an operand, such as a memory offset or a constant. The
first column gives the hexadecimal encoding of the instruction. The second gives
its assembly-language mnemonic. The third gives a brief description of its effect.

Hex Mnemonic Meaning

0x10 BIPUSH byte Push byte onto stack

0x59 DUP Copy top word on stack and push onto stack

0xA7 GOTO offset Unconditional branch

0x60 IADD Pop two words from stack; push their sum

0x7E IAND Pop two words from stack; push Boolean AND

0x99 IFEQ offset Pop word from stack and branch if it is zero

0x9B IFLT offset Pop word from stack and branch if it is less than zero

0x9F IF ICMPEQ offset Pop two words from stack; branch if equal

0x84 IINC varnum const Add a constant to a local variable

0x15 ILOAD varnum Push local variable onto stack

0xB6 INVOKEVIRTUAL disp Invoke a method

0x80 IOR Pop two words from stack; push Boolean OR

0xAC IRETURN Return from method with integer value

0x36 ISTORE varnum Pop word from stack and store in local variable

0x64 ISUB Pop two words from stack; push their difference

0x13 LDC W index Push constant from constant pool onto stack

0x00 NOP Do nothing

0x57 POP Delete word on top of stack

0x5F SWAP Swap the two top words on the stack

0xC4 WIDE Prefix instruction; next instruction has a 16-bit index

Figure 4-11. The IJVM instruction set. The operands byte , const , and varnum
are 1 byte. The operands disp , index , and offset are 2 bytes.
Instructions are provided to push a word from various sources onto the stack.
These sources include the constant pool ( LDC W ), the local variable frame ( ILOAD ),
and the instruction itself ( BIPUSH ). A variable can also be popped from the stack
and stored into the local variable frame ( ISTORE ). Two arithmetic operations ( IADD
and ISUB ) as well as two logical (Boolean) operations ( IAND and IOR ) can be per-
formed using the two top words on the stack as operands. In all the arithmetic and
logical operations, two words are popped from the stack and the result pushed back
onto it. Four branch instructions are provided, one unconditional ( GOTO ) and three
conditional ones ( IFEQ , IFLT , and IF ICMPEQ ). All the branch instructions, if taken,
adjust the value of PC by the size of their (16-bit signed) offset, which follows the
opcode in the instruction. This offset is added to the address of the opcode. There