Peter Cordes

Halifax, Canada

GNU/Linux hacker and command line junkie.

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

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

performance assembly x86 intel cpu-architecture asked Mar 2, 2016 at 9:01

stackoverflow.com

68 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, 2017 at 4:20

stackoverflow.com

48 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, 2017 at 12:05

stackoverflow.com

32 votes

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

assembly x86 sse simd avx asked Jan 29, 2016 at 12:52

stackoverflow.com

30 votes

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

x86 atomic sse avx avx512 asked Sep 2, 2017 at 9:56

stackoverflow.com

19 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, 2020 at 10:57

stackoverflow.com

17 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, 2015 at 3:35

stackoverflow.com

15 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, 2015 at 8:16

stackoverflow.com

15 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, 2015 at 3:34

stackoverflow.com

14 votes

How to convert a binary integer number to a hex string?

assembly x86 hex simd avx512 asked Dec 17, 2018 at 22:14

stackoverflow.com

Top Answers

2085

Why does C++ code for testing the Collatz conjecture run faster than hand-written assembly?

stackoverflow.com

423

Deoptimizing a program for the pipeline in Intel Sandybridge-family CPUs

stackoverflow.com

315

Does the C++ standard allow for an uninitialized bool to crash a program?

stackoverflow.com

301

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

stackoverflow.com

267

How much of ‘What Every Programmer Should Know About Memory’ is still valid?

stackoverflow.com

236

Can num++ be atomic for 'int num'?

stackoverflow.com

176

Bubble sort slower with -O3 than -O2 with GCC

stackoverflow.com

175

Why does glibc's strlen need to be so complicated to run quickly?

stackoverflow.com

140

How to remove "noise" from GCC/clang assembly output?

stackoverflow.com

137

Fastest way to do horizontal SSE vector sum (or other reduction)

stackoverflow.com

127

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

stackoverflow.com

106

Why does preset "veryfast" in FFmpeg generate the most compressed file compared to all other presets?

superuser.com

103

Possible GCC bug when returning struct from a function

stackoverflow.com

Why does my browser think that https://1.1.1.1 is secure?

superuser.com

Where is the x86-64 System V ABI documented?

stackoverflow.com

INC instruction vs ADD 1: Does it matter?

stackoverflow.com

Argument order to std::min changes compiler output for floating-point

stackoverflow.com

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

stackoverflow.com

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

stackoverflow.com

Why is integer assignment on a naturally aligned variable atomic on x86?

stackoverflow.com

Why is this seemingly slower C loop actually twice as fast as the other way?

stackoverflow.com

Where is the lock for a std::atomic?

stackoverflow.com

Floating point division vs floating point multiplication

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Why are loops always compiled into "do...while" style (tail jump)?

stackoverflow.com

gcc optimization flag -O3 makes code slower than -O2

stackoverflow.com

32-bit absolute addresses no longer allowed in x86-64 Linux?

stackoverflow.com

Why are leap seconds needed so often?

physics.stackexchange.com

Can x86's MOV really be "free"? Why can't I reproduce this at all?

stackoverflow.com

What is callq instruction?

stackoverflow.com

How to optimize these loops (with compiler optimization disabled)?

stackoverflow.com