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Andrea Bigagli abigagli

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  • Florence - Italy
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@shafik
shafik / WhatIsStrictAliasingAndWhyDoWeCare.md
Last active June 17, 2024 09:54
What is Strict Aliasing and Why do we Care?

What is the Strict Aliasing Rule and Why do we care?

(OR Type Punning, Undefined Behavior and Alignment, Oh My!)

What is strict aliasing? First we will describe what is aliasing and then we can learn what being strict about it means.

In C and C++ aliasing has to do with what expression types we are allowed to access stored values through. In both C and C++ the standard specifies which expression types are allowed to alias which types. The compiler and optimizer are allowed to assume we follow the aliasing rules strictly, hence the term strict aliasing rule. If we attempt to access a value using a type not allowed it is classified as undefined behavior(UB). Once we have undefined behavior all bets are off, the results of our program are no longer reliable.

Unfortunately with strict aliasing violations, we will often obtain the results we expect, leaving the possibility the a future version of a compiler with a new optimization will break code we th

@shafik
shafik / bit_cast_array.md
Last active June 29, 2021 14:45
How to use bit_cast to type pun a unsigned char array

In C++20 we will hopefully get bit_cast see the proposal and reference implementation. This utility should give us a simple and safe way to type pun.

The one issue I ran into with this utility is that is requires the size of the To and From type to be the same, as well as checking that To and From types are trivially copyable. The static_assert version of the check is as follows:

# define BIT_CAST_STATIC_ASSERTS(TO, FROM) do {                         \
    static_assert(sizeof(TO) == sizeof(FROM));                          \             
    static_assert(std::is_trivially_copyable<TO>::value);               \
    static_assert(std::is_trivially_copyable<FROM>::value);             \
} while (false)
@Starl1ght
Starl1ght / main.cpp
Created March 26, 2017 21:32
Console
#include <vector>
#include <sstream>
#include <iostream>
#include <iterator>
#include <tuple>
template <typename T>
std::vector<std::string> Split(T&& input) {
std::stringstream ss{ std::forward<T>(input) };
return std::vector<std::string> {std::istream_iterator<std::string>(ss), std::istream_iterator<std::string>{} };
@MadLittleMods
MadLittleMods / realtek-rtl-8153-driver-osx-info.md
Last active May 3, 2024 07:57
@rygorous
rygorous / gist:e0f055bfb74e3d5f0af20690759de5a7
Created May 8, 2016 06:54
A bit of background on compilers exploiting signed overflow
Why do compilers even bother with exploiting undefinedness signed overflow? And what are those
mysterious cases where it helps?
A lot of people (myself included) are against transforms that aggressively exploit undefined behavior, but
I think it's useful to know what compiler writers are accomplishing by this.
TL;DR: C doesn't work very well if int!=register width, but (for backwards compat) int is 32-bit on all
major 64-bit targets, and this causes quite hairy problems for code generation and optimization in some
fairly common cases. The signed overflow UB exploitation is an attempt to work around this.
@CMCDragonkai
CMCDragonkai / memory_layout.md
Last active June 17, 2024 12:05
Linux: Understanding the Memory Layout of Linux Executables

Understanding the Memory Layout of Linux Executables

Required tools for playing around with memory:

  • hexdump
  • objdump
  • readelf
  • xxd
  • gcore
@mackuba
mackuba / wwdc15.md
Last active August 6, 2022 17:28
New stuff from WWDC 2015

Here's my own list of the interesting stuff announced during this year's WWDC, collected from the keynotes, various Apple docs, blog posts and tweets.

If you're planning to watch the videos, I really recommend this Mac app that helps you download and watch them: https://github.com/insidegui/WWDC.

OS X El Capitan

http://www.apple.com/osx/elcapitan-preview/

  • split view - two apps side by side on full screen
@rmartinho
rmartinho / gist:15e4f2e48f2a746ee256
Last active August 29, 2015 14:07
Constexpr myths
// Myth #1: constexpr is the same as const
// (note: there is a difference between C++11 and C++14 here)
// (see: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3598.html)
namespace myth1 {
struct foo {
int i;
constexpr int& get() { return i; } // not a const function
}
int f() {
@gmccreight
gmccreight / master.vim
Last active June 19, 2024 15:30
A script that gives you a playground for mastering vim
" copy all this into a vim buffer, save it, then...
" source the file by typing :so %
" Now the vim buffer acts like a specialized application for mastering vim
" There are two queues, Study and Known. Depending how confident you feel
" about the item you are currently learning, you can move it down several
" positions, all the way to the end of the Study queue, or to the Known
" queue.
" type ,, (that's comma comma)