pervognsen

Multi-dimensional array views for systems programmers

As C programmers, most of us think of pointer arithmetic for multi-dimensional arrays in a nested way:

The address for a 1-dimensional array is base + x. The address for a 2-dimensional array is base + x + y*x_size for row-major layout and base + y + x*y_size for column-major layout. The address for a 3-dimensional array is base + x + (y + z*y_size)*x_size for row-column-major layout. And so on.

sebbbi

void BFD2(inout ParticleSimulationData Particle, float3 Accel)
{
	float3 x = Particle.Position;
	float3 v = Particle.Velocity;

	float3 x1 = Particle.PositionPrev;
	float3 v1 = Particle.VelocityPrev;

	Particle.Position = (4.0/3.0) * x - (1.0/3.0) * x1 + 1.0 * ((8.0/9.0) * v - (2.0/9.0) * v1 + (4.0/9.0) * TimeStep2 * Accel);
	Particle.PositionPrev = x;

mbinna

Effective Modern CMake

Getting Started

For a brief user-level introduction to CMake, watch C++ Weekly, Episode 78, Intro to CMake by Jason Turner. LLVM’s CMake Primer provides a good high-level introduction to the CMake syntax. Go read it now.

After that, watch Mathieu Ropert’s CppCon 2017 talk Using Modern CMake Patterns to Enforce a Good Modular Design (slides). It provides a thorough explanation of what modern CMake is and why it is so much better than “old school” CMake. The modular design ideas in this talk are based on the book [Large-Scale C++ Software Design](https://www.amazon.de/Large-Scale-Soft

williballenthin

import os
import sys
import logging

import pefile
import ucutils
import unicorn
import capstone
import argparse

marcan

#!/usr/bin/python3
#
# Simple Bloom filter implementation in Python 3
# Copyright 2017 Hector Martin "marcan" <marcan@marcan.st>
# Licensed under the terms of the MIT license
#
# Written to be used with the Have I been pwned? password list:
#   https://haveibeenpwned.com/passwords
#
# Download the pre-computed filter here (968MB, k=11, false positive p=0.0005):

pervognsen

One thing that surprises newer programmers is that the older 8-bit microcomputers from the 70s and 80s were designed to run at the speed of random memory access to DRAM and ROM. The C64 was released in 1982 when I was born and its 6502 CPU ran at 1 MHz (give or take depending on NTSC vs PAL). It had a 2-stage pipelined design that was designed to overlap execution and instruction fetch for the current and next instruction. Cycle counting was simple to understand and master since it was based almost entirely on the number of memory accesses (1 cycle each), with a 1-cycle penalty for taken branches because of the pipelined instruction fetch for the next sequential instruction. So, the entire architecture was based on keeping the memory subsystem busy 100% of the time by issuing a read or write every cycle. One-byte instructions with no memory operands like INX still take the minimum 2 cycles per instruction and end up redundantly issuing the same memory request two cycles in a row.

pervognsen

Let's study the similarities between two kinds of entropy coders.

ZPAQ-style binary arithmetic coder (taken from Fabian's mini_arith repository):

    int decode(uint32_t prob)
    {
        int bit;

        // Midpoint of active probability interval subdivided via prob
        uint32_t x = lo + ((uint64_t(hi - lo) * prob) >> kProbBits);

martinmoene

// Sean Parent. Inheritance Is The Base Class of Evil. Going Native 2013
// Video: https://www.youtube.com/watch?v=bIhUE5uUFOA
// Code : https://github.com/sean-parent/sean-parent.github.io/wiki/Papers-and-Presentations

/*
    Copyright 2013 Adobe Systems Incorporated
    Distributed under the MIT License (see license at
    http://stlab.adobe.com/licenses.html)

    This file is intended as example code and is not production quality.

brendanzab

NOTE: This was first authored on 26 Feb 2014. Things may have changed since then.

C++'s Templates

C++'s templates could be seen as forming a duck typed, purely functional code generation program that is run at compile time. Types are not checked at the initial invocation stage, rather the template continues to expand until it is either successful, or runs into an operation that is not supported by that specific type – in that case the compiler spits out a 'stack trace' of the state of the template expansion.

To see this in action, lets look at a very simple example:

template