Good explanation! Hacker's Delight by Warren is a great book that explains a lot of these low-level tricks https://www.amazon.com/Hackers-Delight-2nd-Henry-Warren/dp/0321842685 …. Also you may be interested in my slides entitled "Compiler Optimizations for Reverse Engineers"https://www.msreverseengineering.com/blog/2014/6/23/compiler-optimizations-for-reverse-engineers …
While reverse engineering a rootkit sample (That I soon will publish about 
) I saw this weird compiler optimization.
I thought I'll start documenting compiler optimizations for reverse engineers. Read my first article in the series:
https://repnz.github.io/posts/reversing-optimizations-division/ …pic.twitter.com/RufA3fHDa4
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Hey! Actually I've already read your awesome presentation today, thanks! I will certainly order this book.
I also written this for my own documentation and to understand it better;)
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You might want to see the resulting code of different compilers and options, with
@CompileExplore at http://gcc.godbolt.org (thanks again@mattgodbolt ) -
I cover this particular optimisation in my CppCon talk, I think. There's a bunch of them (if not the CppCon talk, it'll be one of the others...)
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Indeed, interesting use of "Unsigned Multiply" to get the address. This is a common optimization on the compiler, for example to make a multiplication: mov ax, 2 ; ax = 2 mov cx, 10 ; cx = 10 mul cx ; ax = ax * cx -> ax = 20
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I'm curious, what rootkit do u mean... It will be interesting to take a look at your analysis.
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Pure gold right here!
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Pretty common optimization scheme
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