DocBohn’s gists

DocBohn / vectorization.c

Last active May 11, 2025 17:49

Code demonstrating hand-crafted and compiler-generated vectorization

	void simple_memory_copy(char restrict destination, char const restrict source, unsigned int length) {
	for (unsigned int i = 0; i < length; i++) {
	destination[i] = source[i];
	}
	}

DocBohn / minimize-loadstore.c

Last active May 5, 2025 17:48

Code demonstrating hand-crafted and compiler-generated migration of redundant loads/stores out of a loop

	void nonoptimizable_accumulate(int accumulator, int const array, int length) {
	for (int i = 0; i < length; i++) {
	*accumulator += array[i];
	}
	}

	void optimizable_accumulate(int restrict accumulator, int const restrict array, int length) {
	for (int i = 0; i < length; i++) {
	*accumulator += array[i];
	}

DocBohn / inlining.c

Created May 5, 2025 16:06

Code demonstrating hand-crafted and compiler-generated function inlining

	static int compute_triangle_number(int base) {
	int base_incremented = base + 1;
	int numerator = base * base_incremented;
	return numerator/2;
	}

	long simple_bonus_threshold(unsigned int number) {
	int triangle_number = compute_triangle_number(number);
	return 3 * triangle_number;
	}

DocBohn / restrict-demonstration.c

Last active May 12, 2025 21:32

Code demonstrating the use of the `restrict` keyword

	#include <string.h>

	void simple_string_copy_without_restrict(char destination, char const source) {
	for (unsigned int i = 0; i <= strlen(source); i++) {
	destination[i] = source[i];
	}
	}

	void simple_string_copy_with_restrict(char restrict destination, char const restrict source) {
	for (unsigned int i = 0; i <= strlen(source); i++) {

DocBohn / pure-function-migration.c

Created May 5, 2025 03:08

Code demonstrating hand-crafted migration of a call to a pure function out of the loop

	#include <string.h>

	size_t strlen(char const *string) [[unsequenced]]; // may help in the future

	void simple_string_copy(char restrict destination, char const restrict source) {
	for (unsigned int i = 0; i < strlen(source); i++) {
	destination[i] = source[i];
	}
	}

DocBohn / loop-invariant-migration.c

Created May 4, 2025 22:58

Code demonstrating hand-crafted and compiler-generated migration of loop-invariant code out of the loop

	void migration(int destination, int const source, int factor, int limit) {
	for (int i = 0; i < limit; i++) {
	destination[factor * limit + i] = source[i];
	}
	}

DocBohn / common-subexpression.c

Last active May 4, 2025 23:01

Code demonstrating hand-crafted and compiler-generated common subexpression elimination

	double average_neighbors(double const *matrix, unsigned int const neighbors[]);

	double no_cse(unsigned int i, unsigned int j, unsigned int width, double values[][width]) {
	unsigned int neighbors[4];
	neighbors[0] = (i-1) * width + j; // values[i-1][j]
	neighbors[1] = (i+1) * width + j; // values[i+1][j]
	neighbors[2] = i * width + (j-1); // values[i][j-1]
	neighbors[3] = i * width + (j+1); // values[i][j+1]
	return average_neighbors((double const *) values, neighbors);
	}

DocBohn / loop_indexing.c

Last active July 26, 2025 13:40

Code that measures the time to iterate over nested arrays

DocBohn / print_stack_address.c

Last active July 25, 2025 21:53

Code that prints the address of a variable that is stored on the stack.

DocBohn / catch-all.c

Created March 19, 2025 15:23

Demonstration of a program that must be killed with a signal other than SIGINT

	#include <stdio.h>
	#include <signal.h>

	void count_loop_iterations(int ignored) ;
	void catch_all(int signal);

	int main() {
	sigaction(SIGINT, &((struct sigaction) {.sa_handler = alarm_handler}), nullptr);
	sigaction(SIGVTALRM, &((struct sigaction) {.sa_handler = alarm_handler}), nullptr);
	count_loop_iterations(2000);

Chris Bohn DocBohn