cKit/Foundation/c_timespec.c

#include <c_timespec.h>
#include <limits.h>

/* ------------------------------------------------------------------------------------------------------------------ */
/*  */


struct timespec c_timespec_mod(struct timespec ts1, struct timespec ts2)
{
	int i = 0;
	bool neg1 = false;
	bool neg2 = false;

	/* Normalise inputs to prevent tv_nsec rollover if whole-second values
	 * are packed in it.
	*/
	ts1 = c_timespec_normalise(ts1);
	ts2 = c_timespec_normalise(ts2);

	/* If ts2 is zero, just return ts1
	*/
	if (ts2.tv_sec == 0 && ts2.tv_nsec == 0)
	{
		return ts1;
	}

	/* If inputs are negative, flip and record sign
	*/
	if (ts1.tv_sec < 0 || ts1.tv_nsec < 0)
	{
		neg1 = true;
		ts1.tv_sec = -ts1.tv_sec;
		ts1.tv_nsec = -ts1.tv_nsec;
	}

	if (ts2.tv_sec < 0 || ts2.tv_nsec < 0)
	{
		neg2 = true;
		ts2.tv_sec = -ts2.tv_sec;
		ts2.tv_nsec = -ts2.tv_nsec;
	}

	/* Shift ts2 until it is larger than ts1 or is about to overflow
	*/
	while ((ts2.tv_sec < (LONG_MAX >> 1)) && c_timespec_ge(ts1, ts2))
	{
		i++;
		ts2.tv_nsec <<= 1;
		ts2.tv_sec <<= 1;
        if (ts2.tv_nsec > C_NSEC_PER_SEC)
        {
            ts2.tv_nsec -= C_NSEC_PER_SEC;
            ts2.tv_sec++;
        }
	}

	/* Division by repeated subtraction
	*/
	while (i >= 0)
	{
		if (c_timespec_ge(ts1, ts2))
		{
			ts1 = c_timespec_sub(ts1, ts2);
		}

		if (i == 0)
		{
			break;
		}

		i--;
		if (ts2.tv_sec & 1)
		{
			ts2.tv_nsec += C_NSEC_PER_SEC;
		}
		ts2.tv_nsec >>= 1;
		ts2.tv_sec >>= 1;
	}

	/* If signs differ and result is nonzero, subtract once more to cross zero
	*/
	if (neg1 ^ neg2 && (ts1.tv_sec != 0 || ts1.tv_nsec != 0))
	{
		ts1 = c_timespec_sub(ts1, ts2);
	}

	/* Restore sign
	*/
	if (neg1)
	{
		ts1.tv_sec = -ts1.tv_sec;
		ts1.tv_nsec = -ts1.tv_nsec;
	}

	return ts1;
}