Sam Stuewe HalosGhost

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

Verifiable brute force strength

Below are table of various projects that can completely exhaust n-bits of keyspace. In other words, counting completely and fully from 0 to 2ⁿ-1.

This Gist implies no discussion about how this is relevant to quantum computing using Grover's algorithm, meet-in-the-middle or birthday attacks, or anything of the like. It's strictly a Gist about raw speed, measuring the result in bits.

If you know of other noteworthy and verifiable brute force searching projects,

Cryptography, not cryptocurrency

	-- Note: There is a more complete explanation at https://github.com/hwayne/lets-prove-leftpad/tree/master/idris
	import Data.Vect

	-- `minus` is saturating subtraction, so this works like we want it to
	eq_max : (n, k : Nat) -> maximum k n = plus (n `minus` k) k
	eq_max n Z = rewrite minusZeroRight n in rewrite plusZeroRightNeutral n in Refl
	eq_max Z (S _) = Refl
	eq_max (S n) (S k) = rewrite sym $ plusSuccRightSucc (n `minus` k) k in rewrite eq_max n k in Refl

	-- The type here says "the result is" padded to (maximum k n), and is padding plus the original

	WAYLAND_PROTOCOLS=/usr/share/wayland-protocols

	# wayland-scanner is a tool which generates C headers and rigging for Wayland
	# protocols, which are specified in XML. wlroots requires you to rig these up
	# to your build system yourself and provide them in the include path.
	xdg-shell-protocol.h:
	wayland-scanner server-header \
	$(WAYLAND_PROTOCOLS)/stable/xdg-shell/xdg-shell.xml $@

	xdg-shell-protocol.c: xdg-shell-protocol.h

	// ==UserScript==
	// @name Zoom Web Client Auto Redirect
	// @namespace https://zoom.us
	// @version 0.1
	// @description Automatically redirect Zoom meetings to the web client
	// @author Mohamad Safadieh
	// @license GNU AGPLv3: https://www.gnu.org/licenses/agpl-3.0.en.html
	// @include /https:\/\/([a-z0-9\-]+\.)?zoom\.us\/([sj])\/([0-9]+).*/
	// @grant none
	// ==/UserScript==

Sam Stuewe HalosGhost

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

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

Verifiable brute force strength

Cryptography, not cryptocurrency

Books

Resources