65
votes
4
answers
1.7K
views
Why does Windows64 use a different calling convention from all other OSes on x86-64?
AMD has an ABI specification that describes the calling convention to use on x86-64. All OSes follow it, excep
60
votes
3
answers
2.7K
views
Possible GCC bug when returning struct from a function
I believe I found a bug in GCC while implementing O'Neill's PCG PRNG. (Initial code on Godbolt'
63
votes
4
answers
970
views
Why do x86-64 instructions on 32-bit registers zero the upper part of the full 64-bit register?
In the x86-64 Tour of Intel Manuals, I read Perhaps the most surprising fact is that an instruction such a
54
votes
4
answers
2K
views
What are the calling conventions for UNIX & Linux system calls (and user-space functions) on i386 and x86-64
Following links explain x86-32 system call conventions for both UNIX (BSD flavor) & Linux: http://www.int
56
votes
4
answers
3K
views
Why would introducing useless MOV instructions speed up a tight loop in x86_64 assembly?
Background: While optimizing some Pascal code with embedded assembly language, I noticed an unnecessary MOV i
62
votes
5
answers
2.4K
views
Why does GCC use multiplication by a strange number in implementing integer division?
I've been reading about div and mul assembly operations, and I decided to see them in action by writing a
52
votes
4
answers
660
views
How do I achieve the theoretical maximum of 4 FLOPs per cycle?
How can the theoretical peak performance of 4 floating point operations (double precision) per cycle be achiev
64
votes
17
answers
1.4K
views
What's the purpose of the LEA instruction?
For me, it just seems like a funky MOV. What's its purpose and when should I use it?