Exercise 2: Identifying Base/Index/Scale/Displacement in [RDI + RCX*8] — Possible Solution
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ASSEMBLY2-4'S OWN SIB FORMULA
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effective address = Base + (Index x Scale) + Displacement

MAPPING THIS CAPSTONE'S INSTRUCTION ONTO THAT FORMULA
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The instruction is: ADD RAX, [RDI + RCX*8]

  Base         = RDI  — holds the array's own starting address
                 (loaded via LEA RDI, [rel array] earlier in the
                 program)

  Index        = RCX  — the loop's own running index, incrementing
                 by 1 each pass (0, 1, 2, 3, 4)

  Scale        = 8    — the multiplier applied to the index, matching
                 the 8-byte width of each qword element in the array
                 (declared with dq, per this chapter's own data
                 section)

  Displacement = (none present) — this particular instruction doesn't
                 use a displacement term at all; per assembly2-4's own
                 explanation, every SIB component is individually
                 optional, and this instruction simply doesn't need
                 one since the array's base address in RDI already
                 points exactly at element 0

WHY SCALE IS SPECIFICALLY 8 HERE
------------------------------
Per assembly2-4's own explanation, Scale must be 1, 2, 4, or 8,
matching byte/word/dword/qword element sizes. Since this capstone's
array holds 64-bit (qword, 8-byte) integers, Scale=8 is exactly the
value needed to convert the index RCX (element number) into the
correct BYTE offset for that element — RCX*8 gives the number of
bytes to skip past the array's start to reach element RCX.

WHY THIS WORKS AS AN ANSWER
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It maps each of the instruction's own components onto assembly2-4's
own formula individually, correctly identifies that no displacement
term is present in this specific instruction, and explains why Scale
is specifically 8 by tying it to the array's own declared element
width (qword, 8 bytes) rather than treating 8 as an arbitrary number.