complex IF statement in assembly

Question

How should I write such an if statement in assembly?

if ((a == b AND a > c) OR c == b) { ...

Platform: Intel 32-bit machine, NASM syntax.

Update

For variable types and value, use whatever is more easy to understand. Integers would works fine for me, I guess.

Answer 1

For a simple expression with no side effects (such as the one given), the order of evaluation does not matter⁽¹⁾. That means you can check the "quick" cases first (those that decide with least code executed, c == b in this case).

In generic assembly, it will be basically something like this (assume a in ax, b in bx, c in cx):

    cmp  bx, cx     ; check b == c?
    jeq  is_true    ; final result is true.

    cmp  ax, cx     ; otherwise b != c, so check a <= c?
    jle  is_false   ; if so, final result is false.

    cmp  ax, bx     ; otherwise a > c, so check a == b?
    jeq  is_true    ; if so, final result is true.

is_false:
    ; do false bit  ; otherwise final result is false.
    jmp  next

is_true:
    ; do true bit

next:
    ; carry on

If there's no false bit, it can be simplified to something like:

    cmp  bx, cx
    jeq  is_true

    cmp  ax, bx
    jne  next      ; no false bit, next statement.

    cmp  ax, cx
    jle  next      ; no false bit, next statement.

is_true:
    ; do true bit

next:
    ; carry on

---

⁽¹⁾ If the expression contained side-effects then order of evaluation may become important due to the possibility of short-circuiting evaluations. By that, I mean consider an expression such as (pseudo-code):

if a == b and c == d:
    do_something()

In that case, once you establish that a and b are equal, there is no need to compare c and d.

I haven't covered that (other than in this footnote) since:

1. no source language was specified in the question (making it unclear whether it even has short-circuiting operations); and

2. the expression appears to have no side effects anyway.