Pascal's triangle

pascal.c

#include <inttypes.h>
#include <math.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#ifdef _WIN32
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#endif

#define SEPARATOR_SIZE 2

uint64_t GetMillis()
{
#ifdef _WIN32
	SYSTEMTIME sysTime = { 0 };
	FILETIME realTime = { 0 };
	GetSystemTime(&sysTime);
	SystemTimeToFileTime(&sysTime, &realTime);
	return *(uint64_t*)&realTime / 10000; // 100-nanosecond intervals to milliseconds
#else
	struct timespec now = { 0 };
	clock_gettime(CLOCK_MONOTONIC, &now);
	return now.tv_sec * 1000 + now.tv_nsec / 1000000;
#endif
}

__forceinline long double Term(long double n, long double k, long double last)
{
	return last * (n + 1 - k) / k;
}

__forceinline uint32_t RowLength(uint32_t n)
{
	uint32_t length = 0;
	long double last = 1;
	for (uint32_t k = 1; k <= n; k++)
	{
		last = Term(n, k, last);
		length += floorl(log10l(last)) + SEPARATOR_SIZE;
	}

	return length;
}

int main(int argc, char* argv[])
{
	uint32_t rows = 10;
	if (argc > 1)
	{
		rows = (uint32_t)strtoul(argv[1], NULL, 10);
	}

	uint32_t first = 0;
	if (argc > 2)
	{
		if (strcmp(argv[2], "last") == 0)
		{
			first = rows;
		}
		first = (uint32_t)strtoul(argv[2], NULL, 10);
	}

	uint32_t columnLimit = 80;
	if (argc > 3)
	{
		columnLimit = (uint32_t)strtoul(argv[3], NULL, 10);
	}

	printf("Computing rows %d-%d (%d total)\n", first, rows, (rows - first));

	uint64_t start = rows > 1000 ? time(NULL) : GetMillis();
	uint32_t maxLength = RowLength(rows);
	bool center = maxLength <= columnLimit; // reasonable terminal size
	if (center)
	{
		printf("Centering because last row is within column limit (%u < %u)\n", maxLength, columnLimit);
	}
	for (uint32_t n = first; n < rows + 1; n++)
	{
		printf("row %4d: %*s", n, center ? (uint32_t)((maxLength - RowLength(n)) * 0.5) : 0, "");
		long double last = 1;
		for (long double k = 1; k <= n; k++)
		{
			printf("%.00Lf%*s", last, center ? SEPARATOR_SIZE : 1, "");
			last = Term(n, k, last);
		}
		printf("%.00Lf\n", last);
	}
	uint64_t end = rows > 1000 ? time(NULL) : GetMillis();

	printf("Computed %d rows in %.03fs\n", rows - first, (end - start) / (rows > 1000 ? 1.0f : 1000.0f));

	return rows;
}