alwynallan

// https://www.reddit.com/r/RNG/comments/19a2q24/collatzweyl_generators/?utm_source=share&utm_medium=web2x&context=3

// $ gcc -Wall -O3 Collatz-Weyl.c -o Collatz-Weyl
// $ ./Collatz-Weyl | pv > /dev/null <-- 650MiB/s on 2018 Zeon VM
//                         compared with 400MiB/s for ChaCha20

#include <stdio.h>
#include <assert.h>

static __uint128_t c[4] = {0, 0, 0, 0}; // c[0] must be odd

alwynallan

/*
https://math.stackexchange.com/a/3306

A simple (practical, low-computation) approach to choosing among three options with 
equal probability exploits the fact that in a run of independent flips of an unbiased 
coin, the chance of encountering THT before TTH occurs is 1/3. So:

Flip a coin repeatedly, keeping track of the last three outcomes. (Save time, if you 
like, by assuming the first flip was T and proceeding from there.)

alwynallan

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

int compare (const void * a, const void * b)
{
  if (*(double*)a > *(double*)b) return 1;
  else if (*(double*)a < *(double*)b) return -1;
  else return 0;
}

alwynallan

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

int compare (const void * a, const void * b)
{
  if (*(double*)a > *(double*)b) return 1;
  else if (*(double*)a < *(double*)b) return -1;
  else return 0;
}

alwynallan

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

int compare (const void * a, const void * b)
{
  if (*(double*)a > *(double*)b) return 1;
  else if (*(double*)a < *(double*)b) return -1;
  else return 0;
}

alwynallan

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <assert.h>

// alwynallan@gmail.com February 2021
// tests the 64-bit hardware efficient generation of 1-in-3 choices.
// uses the fact that 2^65 is just ~1% larger than 3^41
// whereas            2^2  is      25% larger than 3^1

alwynallan

CC = gcc
RM = rm -f

INSTRUMENT_FOR_PROMETHEUS := false

ifeq ($(INSTRUMENT_FOR_PROMETHEUS),true)
  CFLAGS  = -Wall -DINSTRUMENT_FOR_PROMETHEUS
  LIBS    = -lbcm2835 -lprom -lpromhttp -lmicrohttpd
else
  CFLAGS  = -Wall

alwynallan

/*

Deprecated, see https://gist.github.com/alwynallan/1c13096c4cd675f38405702e89e0c536

If you have to use software PWM, it's still here.

*/

alwynallan

{
"servers":[
  {"name":"pool.ntp.org"},
  {"name":"asia.pool.ntp.org"},
  {"name":"europe.pool.ntp.org"},
  {"name":"north-america.pool.ntp.org"},
  {"name":"oceania.pool.ntp.org"},
  {"name":"south-america.pool.ntp.org"}
],
"regions":[

alwynallan

var xmlhttp = new XMLHttpRequest();
var url = "http://apa.hopto.org/tz_data.json"; // do we need the domain??
var tzArr;

xmlhttp.onreadystatechange = function() {
    if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
        tzArr = JSON.parse(xmlhttp.responseText);
        populateOptions(tzArr);
    }
};