delta = id->nextNotify - id->nextNotify;
delta = id->nextNotify - id->lastNotify;
static PRIntervalTime pr_PredictNextNotifyTime(PRAlarmID *id){    PRIntervalTime delta;    PRFloat64 baseRate = (PRFloat64)id->period / (PRFloat64)id->rate;    PRFloat64 offsetFromEpoch = (PRFloat64)id->accumulator * baseRate;    id->accumulator += 1;  /* every call advances to next period */    id->lastNotify = id->nextNotify;  /* just keeping track of things */    id->nextNotify = (PRIntervalTime)(offsetFromEpoch + 0.5);    delta = id->nextNotify - id->nextNotify;    return delta;}  /* pr_PredictNextNotifyTime */