Dear David,
Right now I'm studying the Poly/ML's interpreter, trying to understand
the semantics of opcodes implemented in interpret.cpp. However, I have
difficulty on understanding some of the opcodes:
1. INSTR_non_local, in its implementation
case INSTR_non_local:
{
PolyWord *t = sp+arg1;
POLYSIGNED uu;
for(uu = 1; uu <= arg2; uu++) t =
(t[-1]).AsStackAddr();
uu = arg3; /* Can be negative. */
if (uu > 32767) uu -= 65536;
*(--sp) = t[uu];
pc += 6;
break;
}
Here what does this instruction do, and what does t[-1] holds? Also
how about the semantics of INSTR_non_local_l_i (where i can be 1, 2 or
3)?
2. INSTR_const_addr_Xb, and INSTR_const_addr_Xw: in their
implementations they have long expression for computing the addresses
such as:
PolyWord::FromCodePtr(pc + (pc[0]+4)*sizeof(PolyWord) + pc[1] + pc[2]*256 + 3))
I'm confused about what does the address computed by the long
expression refer to and why it is computed in this way? What are the
meanings of Xb, and Xw in the their instruction names?
3. INSTR_ldexc. This instruction pushes the content in p_reg[0] into
the stack. I read the definition of the stack object in globals.h, but
still couldn't understand what is the stack registers used for?
Here could you give me some help for understanding the above instructions?
Thanks,
Yue
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