XVilka

THIS GIST WAS MOVED TO TERMSTANDARD/COLORS REPOSITORY.

PLEASE ASK YOUR QUESTIONS OR ADD ANY SUGGESTIONS AS A REPOSITORY ISSUES OR PULL REQUESTS INSTEAD!

lelandbatey

Description

This simple script will take a picture of a whiteboard and use parts of the ImageMagick library with sane defaults to clean it up tremendously.

The script is here:

#!/bin/bash
convert "$1" -morphology Convolve DoG:15,100,0 -negate -normalize -blur 0x1 -channel RBG -level 60%,91%,0.1 "$2"

Results

robindegen

#pragma comment(lib, "Xinput.lib")

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <Xinput.h>

rygorous

// ---- Straightforward:
__m128i lo_int = _mm_and_si128(_mm_set1_epi32(0xffff), in); // low 16 bits of all vals
__m128i hi_int = _mm_srli_epi32(in, 16);   // high 16 bits of all vals
__m128  lo_flt = _mm_cvtepi32_ps(lo_int);  // exact (all 16 bit ints = machine numbers)
__m128  hi_flt = _mm_cvtepi32_ps(hi_int);  // exact
__m128  hi_scl = _mm_mul_ps(hi_flt, _mm_set1_ps(65536.0f)); // exact (just exponent change)
__m128  result = _mm_add_ps(hi_scl, lo_flt); // this is the only step that rounds.

// same approach also works with FMA where available.

paniq

max(-x,-y) = -min(x,y)
min(-x,-y) = -max(x,y)

abs(x) = abs(-x)
abs(x) = max(x,-x) = -min(x,-x)
abs(x*a) = if (a >= 0) abs(x)*a
              (a <  0) -abs(x)*a

// basically any commutative operation
min(x,y) + max(x,y) = x + y

ocornut

// Mini memory editor for Dear ImGui (to embed in your game/tools)
// Animated GIF: https://twitter.com/ocornut/status/894242704317530112

// THE MEMORY EDITOR CODE HAS MOVED TO GIT: 
//   https://github.com/ocornut/imgui_club/tree/master/imgui_memory_editor
// Click "Revisions" on the Gist to see old version.

ocornut

Memory Optimization (Christer Ericson, GDC 2003)
http://realtimecollisiondetection.net/pubs/GDC03_Ericson_Memory_Optimization.ppt

Cache coherency primer (Fabian Giesen)
https://fgiesen.wordpress.com/2014/07/07/cache-coherency/

Code Clinic 2015: How to Write Code the Compiler Can Actually Optimize (Mike Acton)
http://gdcvault.com/play/1021866/Code-Clinic-2015-How-to

m-ou-se

# Download latest archlinux bootstrap package, see https://www.archlinux.org/download/
wget 'ftp://ftp.nluug.nl/pub/os/Linux/distr/archlinux/iso/latest/archlinux-bootstrap-*-x86_64.tar.gz'

# Make sure you'll have enough entropy for pacman-key later.
apt-get install haveged

# Install the arch bootstrap image in a tmpfs.
mount -t tmpfs none /mnt
cd /mnt
tar xvf ~/archlinux-bootstrap-*-x86_64.tar.gz --strip-components=1

pervognsen

/// zzz - very sleepy replacement, based on etw

#define INITGUID
#include <windows.h>
#include <psapi.h>
#include <tdh.h>
#include <evntrace.h>
#include <guiddef.h>
#pragma warning(disable: 4091)
#include <dbghelp.h>

rygorous

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.