alwynallan’s gists

alwynallan / bin2svg.c

Created January 4, 2025 20:13

Takes binary data in 1-byte to 8-byte words and produces a .SVG image of 100K lines where the position on the circumference is the value of each word. Most graphics software balks and the extreme number of transparent objects, but Chrome and Illustrator can handle it, and Inkscape tries.

	// bin2svg.c

	// $ gcc -Wall -O3 bin2svg.c -o bin2svg -lm

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

alwynallan / Collatz-Weyl.c

Created January 21, 2024 23:06

PRNG with seeding and output - see link in code

	// 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 / three_hack.c

Created April 23, 2023 23:28

	/*
	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 / pmg2.c

Created August 31, 2021 07:59

Solution per tstanisl at https://stackoverflow.com/a/68959383/5660198 and pmg's 2nd comment

	#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 / solution.c

Created August 29, 2021 12:33

Solution per tstanisl at https://stackoverflow.com/a/68959383/5660198

	#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 / not_solution.c

Last active August 29, 2021 12:29

Bad attempt at solution per tstanisl at https://stackoverflow.com/a/68959383/5660198

	#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 / thirds.c

Created February 23, 2021 21:51

Tests the 64-bit hardware efficient generation of random 1-in-3 choices.

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

	// [email protected] 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 / Makefile

Last active February 22, 2025 16:37

Hardware PWM Controller for the Raspberry Pi 4 Case Fan

	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 / pi_fan_pwm.c

Last active September 23, 2024 16:31

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

	/*

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

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

	*/

alwynallan / tz_data.json

Created January 17, 2016 23:00

Worldwide timezone data for iotclock.js

	{
	"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":[

Peter Allan alwynallan