OPTIMIZING THE JAVA VIRTUAL MACHINE INSTRUCTION SET BY ...

29
execute (JMethod * method, Slot * callingStack, int callingTop) // 1
{ // 2
Slot * stack = new slot (method.maxStack()) // 3
Slot * locals = new Slot (method.maxLocals()) // 4
// 5
int nps = method.numParamSlots(); // 6
for (int i = 0; i < nps; i++) // 7
{ // 8
locals[i] = callingStack[callingTop-nps+1+i]; // 9
} // 10
// 11
ConstantPool *cp = method.constantPool(); // 12
u1* code = method.code(); // 13
SlotPos pc = 0; // 14
SlotPos npc = 0; // 15
// 16
FDE_LOOP: // 17
pc = npc; // 18
npc += InstructionSize[code[pc]]; // 19
switch (code[pc]) { // 20
... // 21
case op_iload_1: // 22
top++; // 23
stack[top] = locals[1]; // 24
goto FDE_LOOP: // 25
... // 26
case op_iconst_1: // 27
top++; // 28
stack[top] = 1; // 29
goto FDE_LOOP: // 30
... // 31
} // 32
} // 33
Figure 2.10: Implementation of a Simple Virtual Machine
2.6 Implementing a Simple Java Interpreter
This section examines the implementation of a simple Java interpreter. It shows how
the virtual machine’s core data structures interact with the interpreter’s execution
loop. The implementation is shown in low level C-like pseudo code. Some type casts
that would be necessary in a C language implementation have been omitted in order
to improve the clarity of the figure.