Stack Exchange

Peter Cordes

Halifax, Canada

GNU/Linux hacker and command line junkie.

(profile pic is from https://xkcd.com/386/)

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Top Questions
59 votes

Why is the loop instruction slow? Couldn't Intel have implemented it efficiently?

performance assembly x86 intel cpu-architecture asked Mar 2 '16 at 9:01
stackoverflow.com

42 votes

What happens if you use the 32-bit int 0x80 Linux ABI in 64-bit code?

linux assembly x86-64 system-calls abi asked Sep 7 '17 at 4:20
stackoverflow.com

36 votes

How exactly do partial registers on Haswell/Skylake perform? Writing AL seems to have a false dependency on RAX, and AH is inconsistent

assembly x86 intel cpu-architecture micro-optimization asked Aug 13 '17 at 12:05
stackoverflow.com

26 votes

What are the best instruction sequences to generate vector constants on the fly?

assembly x86 sse simd avx asked Jan 29 '16 at 12:52
stackoverflow.com

15 votes

In GNU C inline asm, what're the modifiers for xmm/ymm/zmm for a single operand?

c gcc assembly sse avx512 asked Dec 25 '15 at 3:35
stackoverflow.com

14 votes

Per-element atomicity of vector load/store and gather/scatter?

x86 atomic sse avx avx512 asked Sep 2 '17 at 9:56
stackoverflow.com

13 votes

Which 2's complement integer operations can be used without zeroing high bits in the inputs, if only the low part of the result is wanted?

assembly binary x86 integer twos-complement asked Dec 20 '15 at 3:34
stackoverflow.com

12 votes

Vectorizing with unaligned buffers: using VMASKMOVPS: generating a mask from a misalignment count? Or not using that insn at all

gcc assembly x86 sse avx asked Dec 16 '15 at 8:16
stackoverflow.com

12 votes

ffmpeg: explicitly tag h.264 as bt.601, rather than leaving unspecified?

ffmpeg h.264 colorspace metadata asked Nov 7 '15 at 21:36
video.stackexchange.com

11 votes

Is vxorps-zeroing on AMD Jaguar/Bulldozer/Zen faster with xmm registers than ymm?

assembly x86 avx micro-optimization amd-processor asked May 1 '17 at 1:53
stackoverflow.com

1 2 3

Top Answers
1896
C++ code for testing the Collatz conjecture faster than hand-written assembly - why?
stackoverflow.com

405
Deoptimizing a program for the pipeline in Intel Sandybridge-family CPUs
stackoverflow.com

284
Does the C++ standard allow for an uninitialized bool to crash a program?
stackoverflow.com

217
What is the best way to set a register to zero in x86 assembly: xor, mov or and?
stackoverflow.com

192
Can num++ be atomic for 'int num'?
stackoverflow.com

148
Why does glibc's strlen need to be so complicated to run quickly?
stackoverflow.com

141
What Every Programmer Should Know About Memory?
stackoverflow.com

123
Why does this delay-loop start to run faster after several iterations with no sleep?
stackoverflow.com

102
Possible GCC bug when returning struct from a function
stackoverflow.com

96
Why does my browser think that https://1.1.1.1 is secure?
superuser.com

89
How to remove “noise” from GCC/clang assembly output?
stackoverflow.com

76
Fastest way to do horizontal SSE vector sum (or other reduction)
stackoverflow.com

69
Boolean values as 8 bit in compilers. Are operations on them inefficient?
stackoverflow.com

62
Where is the lock for a std::atomic?
stackoverflow.com

62
Why are leap seconds needed so often?
physics.stackexchange.com

57
Do x86 instructions require their own encoding as well as all of their arguments to be present in memory at the same time?
stackoverflow.com

57
INC instruction vs ADD 1: Does it matter?
stackoverflow.com

49
Where is the x86-64 System V ABI documented?
stackoverflow.com

48
How to force GCC to assume that a floating-point expression is non-negative?
stackoverflow.com

47
Is this floating-point optimization allowed?
stackoverflow.com

47
Why is the Linux kernel 15+ million lines of code?
unix.stackexchange.com

47
C loop optimization help for final assignment (with compiler optimization disabled)
stackoverflow.com

46
The start of x86: Intel 8080 vs Intel 8086?
retrocomputing.stackexchange.com

46
Efficient integer floor function in C++
stackoverflow.com

44
What happens if you use the 32-bit int 0x80 Linux ABI in 64-bit code?
stackoverflow.com

44
32-bit absolute addresses no longer allowed in x86-64 Linux?
stackoverflow.com

42
Why are loops always compiled into “do…while” style (tail jump)?
stackoverflow.com

42
Why is integer assignment on a naturally aligned variable atomic on x86?
stackoverflow.com

41
What is the efficient way to count set bits at a position or lower?
stackoverflow.com

41
Is `~/Documents` a relative or an absolute path?
unix.stackexchange.com

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