naive diff code implementation/reference in c.

haven't managed to write this in rust yet. it's... complicated.

rust/Makefile

@@ -1,3 +1,6 @@
diff_code: diff_code.c
	gcc -std=c99 -o diff_code diff_code.c
keylog: keylog.rs libkeylog_xlib.so
	rustc -L rust-xlib -L . keylog.rs

rust/diff_code.c

@@ -0,0 +1,46 @@
#include <stdio.h>
#include <stdlib.h>
int* diff_encode(int* values, int length) {
	if (length < 1) {
		return NULL;
	}
	int* result = malloc(sizeof(int) * length);
	int last = result[0] = values[0];
	for (int i = 1; i < length; i++) {
		result[i] = values[i] - last;
		last = values[i];
	}
	return result;
}
int* diff_decode(int* encoded, int length) {
	if (length < 1) {
		return NULL;
	}
	int* result = malloc(sizeof(int) * length);
	int last = result[0] = encoded[0];
	for (int i = 1; i < length; i++) {
		result[i] = last + encoded[i];
		last = result[i];
	}
	return result;
}
int main() {
	int years[] = {1913, 2020, 1931, 1947, 1978, 1970, 2001, 2023, 1801, 2807};
	int length = 10;
	int* encoded = diff_encode(years, length);
	int* decoded = diff_decode(encoded, length);
	for (int i = 0; i < length; i++) {
		printf("%d -> %d -> %d\n", years[i], encoded[i], decoded[i]);
	}
	return 0;
}