IntervalTimerState.h

/*
 * Copyright (c) 2026, Pedigree Developers
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted.
 */
 
#ifndef PEDIGREE_MODULES_POSIX_INTERVALTIMERSTATE_H
#define PEDIGREE_MODULES_POSIX_INTERVALTIMERSTATE_H
#include "pedigree/kernel/time/Time.h"
 
#include <config.h>
 
namespace PosixIntervalTimerState {
struct Consumption {
  Time::Timestamp value;
  bool armed;
  bool expired;
};
 
struct AbsoluteConsumption {
  Consumption timer;
  Time::Timestamp baseline;
};
 
inline Consumption consume(Time::Timestamp value, Time::Timestamp interval, bool armed,
                           Time::Timestamp elapsed) {
  if (!armed || !elapsed) {
    return {value, armed, false};
  }
  if (elapsed < value) {
    return {value - elapsed, true, false};
  }
  if (!interval) {
    return {0, false, true};
  }
 
  const Time::Timestamp overshoot = elapsed - value;
  const Time::Timestamp phase = overshoot % interval;
  return {phase ? interval - phase : interval, true, true};
}
 
inline AbsoluteConsumption consumeAbsolute(Time::Timestamp value, Time::Timestamp interval,
                                           bool armed, Time::Timestamp baseline,
                                           Time::Timestamp current) {
  if (current <= baseline) {
    return {{value, armed, false}, baseline};
  }
 
  return {consume(value, interval, armed, current - baseline), current};
}
}  // namespace PosixIntervalTimerState
 
#endif