timespec arithmetic

gistfile1.txt

#define NS_IN_SEC 1000000000
// I bet there's a subtle overflow bug somewhere here
static inline struct timespec timespec_add(const struct timespec * restrict a, const struct timespec * restrict b)
{
    unsigned long nsecs = (a->tv_nsec % NS_IN_SEC) + (b->tv_nsec % NS_IN_SEC);
    struct timespec result = {
        a->tv_sec + b->tv_sec + (a->tv_nsec / NS_IN_SEC) + (b->tv_nsec / NS_IN_SEC) + (nsecs / NS_IN_SEC),
        nsecs % NS_IN_SEC
    };

    return result;
}

static inline struct timespec timespec_diff(const struct timespec * restrict a, const struct timespec * restrict b)
{
    if(a->tv_nsec < b->tv_nsec)
    {
        struct timespec result = {
            a->tv_sec - b->tv_sec - 1,
            NS_IN_SEC + a->tv_nsec - b->tv_nsec,
        };
        return result;
    } else
    {
        struct timespec result = {
            a->tv_sec - b->tv_sec,
            a->tv_nsec - b->tv_nsec,
        };
        return result;
    }
}

static inline struct timespec timespec_mad(const struct timespec * restrict a, const struct timespec * restrict b, uint64_t c)
{
    // TODO: replace this with something close to O(1)
    struct timespec result = *a;
    for(uint64_t i = 0; i < c; ++i)
        result = timespec_add(&result, b);
    return result;
}