Sometimes, in order to understand a tricky piece of C/C++ code, you have to compile it. And sometimes, assembly code is easier to grasp.
There are couple of my histories, when I compiled something to understand it better.
David Litchfield in his The Oracle Hacker's Handbook: Hacking and Defending Oracle book:
wordlen -= wordlen & 1;
I used C compiler + IDA to understand this. But today you can use Godbolt's compiler explorer, of course.
mov eax, edi and eax, -2 ret
-2 is 0xffff....fffe. So this code, in other words, clears the lower bit, and it would be possible to simplify it to:
wordlen = wordlen & 1;
(Without subtraction.) It seems, David Litchfield meant aligning by 2-byte boundary.
(UPD: Ouch! A typo. My bad. Thanks, masklinn at reddit. Correct would be : wordlen & ~1.)
Now my all-time favorite from SAT0W SAT solver by Donald Knuth:
p += p+(i&1)+2;
This is pretty close to IOCCC contests.
and esi, 1 lea eax, [rsi+2+rdi*2] ret
esi&1 + 2 + rdi*2
p = i&1 + 2 + p*2
More examples in my book.
(UPD: as seen at reddit.)
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