Is a switch statement actually faster than an if statement? I ran the code below on Visual Studio 2010’s x64 C++ compiler with the /Ox flag: #include <stdlib.h> #include <stdio.h> #include <time.h> #define MAX_COUNT (1 << 29) size_t counter = 0; size_t testSwitch() { clock_t start = clock(); size_t i; for (i = 0; i … Read more
Once upon a time, to write x86 assembler, for example, you would have instructions stating “load the EDX register with the value 5”, “increment the EDX” register, etc. With modern CPUs that have 4 cores (or even more), at the machine code level does it just look like there are 4 separate CPUs (i.e. are … Read more
I am working on some Java code which needs to be highly optimized as it will run in hot functions that are invoked at many points in my main program logic. Part of this code involves multiplying double variables by 10 raised to arbitrary non-negative int exponents. One fast way (edit: but not the fastest … Read more
How do you run a program all by itself without an operating system running? Can you create assembly programs that the computer can load and run at startup, e.g. boot the computer from a flash drive and it runs the program that is on the CPU? 4 Answers 4
A friend of mine downloaded some malware from Facebook, and I’m curious to see what it does without infecting myself. I know that you can’t really decompile an .exe, but can I at least view it in Assembly or attach a debugger? Edit to say it is not a .NET executable, no CLI header. 16 … Read more
I was wondering how to use GCC on my C source file to dump a mnemonic version of the machine code so I could see what my code was being compiled into. You can do this with Java but I haven’t been able to find a way with GCC. I am trying to re-write a … Read more
How does one do this? If I want to analyze how something is getting compiled, how would I get the emitted assembly code? 17 s 17 Use the -S option to gcc (or g++), optionally with -fverbose-asm which works well at the default -O0 to attach C names to asm operands as comments. Less well … Read more
Closed. This question needs to be more focused. It is not currently accepting answers. Closed 11 months ago. Locked. This question and its answers are locked because the question is off-topic but has historical significance. It is not currently accepting new answers or interactions. One of the stated reasons for knowing assembler is that, on … Read more
How can the theoretical peak performance of 4 floating point operations (double precision) per cycle be achieved on a modern x86-64 Intel CPU? As far as I understand it takes three cycles for an SSE add and five cycles for a mul to complete on most of the modern Intel CPUs (see for example Agner … Read more
For me, it just seems like a funky MOV. What’s its purpose and when should I use it? 17 s 17
