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
67 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

51 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

40 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

28 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

16 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

15 votes

In GNU C inline asm, what are the size-override modifiers for xmm/ymm/zmm for a single operand?

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

13 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

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

13 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

Does modern PC video hardware support VGA text mode in HW, or does the BIOS emulate it (with System Management Mode)?

performance assembly x86-16 bios vga asked Apr 30 '20 at 10:57
stackoverflow.com

1 2 3

Top Answers
1938
Why does C++ code for testing the Collatz conjecture run faster than hand-written assembly?
stackoverflow.com

408
Deoptimizing a program for the pipeline in Intel Sandybridge-family CPUs
stackoverflow.com

294
Does the C++ standard allow for an uninitialized bool to crash a program?
stackoverflow.com

245
What is the best way to set a register to zero in x86 assembly: xor, mov or and?
stackoverflow.com

204
Can num++ be atomic for 'int num'?
stackoverflow.com

172
What Every Programmer Should Know About Memory?
stackoverflow.com

156
Why does glibc's strlen need to be so complicated to run quickly?
stackoverflow.com

125
Why does this delay-loop start to run faster after several iterations with no sleep?
stackoverflow.com

106
How to remove “noise” from GCC/clang assembly output?
stackoverflow.com

103
Possible GCC bug when returning struct from a function
stackoverflow.com

97
Why does my browser think that https://1.1.1.1 is secure?
superuser.com

89
Fastest way to do horizontal SSE vector sum (or other reduction)
stackoverflow.com

83
Why does preset “veryfast” in FFmpeg generate the most compressed file compared to all other presets?
superuser.com

78
Argument order to std::min changes compiler output for floating-point
stackoverflow.com

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

66
Where is the lock for a std::atomic?
stackoverflow.com

64
INC instruction vs ADD 1: Does it matter?
stackoverflow.com

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

60
Where is the x86-64 System V ABI documented?
stackoverflow.com

59
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

58
What happens if you use the 32-bit int 0x80 Linux ABI in 64-bit code?
stackoverflow.com

52
32-bit absolute addresses no longer allowed in x86-64 Linux?
stackoverflow.com

50
Why are loops always compiled into “do…while” style (tail jump)?
stackoverflow.com

50
How to force GCC to assume that a floating-point expression is non-negative?
stackoverflow.com

49
Is this floating-point optimization allowed?
stackoverflow.com

49
Why is integer assignment on a naturally aligned variable atomic on x86?
stackoverflow.com

49
Why is the Linux kernel 15+ million lines of code?
unix.stackexchange.com

48
The start of x86: Intel 8080 vs Intel 8086?
retrocomputing.stackexchange.com

48
What is callq instruction?
stackoverflow.com

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

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