#ifndef __NET_SCHED_RED_H
  #define __NET_SCHED_RED_H
  
  #include <linux/types.h>
  #include <linux/bug.h>
  #include <net/pkt_sched.h>
  #include <net/inet_ecn.h>
  #include <net/dsfield.h>
  #include <linux/reciprocal_div.h>
  
  /*	Random Early Detection (RED) algorithm.
  	=======================================
  
  	Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways
  	for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking.
  
  	This file codes a "divisionless" version of RED algorithm
  	as written down in Fig.17 of the paper.
  
  	Short description.
  	------------------
  
  	When a new packet arrives we calculate the average queue length:
  
  	avg = (1-W)*avg + W*current_queue_len,
  
  	W is the filter time constant (chosen as 2^(-Wlog)), it controls
  	the inertia of the algorithm. To allow larger bursts, W should be
  	decreased.
  
  	if (avg > th_max) -> packet marked (dropped).
  	if (avg < th_min) -> packet passes.
  	if (th_min < avg < th_max) we calculate probability:
  
  	Pb = max_P * (avg - th_min)/(th_max-th_min)
  
  	and mark (drop) packet with this probability.
  	Pb changes from 0 (at avg==th_min) to max_P (avg==th_max).
  	max_P should be small (not 1), usually 0.01..0.02 is good value.
  
  	max_P is chosen as a number, so that max_P/(th_max-th_min)
  	is a negative power of two in order arithmetics to contain
  	only shifts.
  
  
  	Parameters, settable by user:
  	-----------------------------
  
  	qth_min		- bytes (should be < qth_max/2)
  	qth_max		- bytes (should be at least 2*qth_min and less limit)
  	Wlog	       	- bits (<32) log(1/W).
  	Plog	       	- bits (<32)
  
  	Plog is related to max_P by formula:
  
  	max_P = (qth_max-qth_min)/2^Plog;
  
  	F.e. if qth_max=128K and qth_min=32K, then Plog=22
  	corresponds to max_P=0.02
  
  	Scell_log
  	Stab
  
  	Lookup table for log((1-W)^(t/t_ave).
  
  
  	NOTES:
  
  	Upper bound on W.
  	-----------------
  
  	If you want to allow bursts of L packets of size S,
  	you should choose W:
  
  	L + 1 - th_min/S < (1-(1-W)^L)/W
  
  	th_min/S = 32         th_min/S = 4
  
  	log(W)	L
  	-1	33
  	-2	35
  	-3	39
  	-4	46
  	-5	57
  	-6	75
  	-7	101
  	-8	135
  	-9	190
  	etc.
   */
  
  /*
   * Adaptative RED : An Algorithm for Increasing the Robustness of RED's AQM
   * (Sally FLoyd, Ramakrishna Gummadi, and Scott Shenker) August 2001
   *
   * Every 500 ms:
   *  if (avg > target and max_p <= 0.5)
   *   increase max_p : max_p += alpha;
   *  else if (avg < target and max_p >= 0.01)
   *   decrease max_p : max_p *= beta;
   *
   * target :[qth_min + 0.4*(qth_min - qth_max),
   *          qth_min + 0.6*(qth_min - qth_max)].
   * alpha : min(0.01, max_p / 4)
   * beta : 0.9
   * max_P is a Q0.32 fixed point number (with 32 bits mantissa)
   * max_P between 0.01 and 0.5 (1% - 50%) [ Its no longer a negative power of two ]
   */
  #define RED_ONE_PERCENT ((u32)DIV_ROUND_CLOSEST(1ULL<<32, 100))
  
  #define MAX_P_MIN (1 * RED_ONE_PERCENT)
  #define MAX_P_MAX (50 * RED_ONE_PERCENT)
  #define MAX_P_ALPHA(val) min(MAX_P_MIN, val / 4)
  
  #define RED_STAB_SIZE	256
  #define RED_STAB_MASK	(RED_STAB_SIZE - 1)
  
  struct red_stats {
  	u32		prob_drop;	/* Early probability drops */
  	u32		prob_mark;	/* Early probability marks */
  	u32		forced_drop;	/* Forced drops, qavg > max_thresh */
  	u32		forced_mark;	/* Forced marks, qavg > max_thresh */
  	u32		pdrop;          /* Drops due to queue limits */
  	u32		other;          /* Drops due to drop() calls */
  };
  
  struct red_parms {
  	/* Parameters */
  	u32		qth_min;	/* Min avg length threshold: Wlog scaled */
  	u32		qth_max;	/* Max avg length threshold: Wlog scaled */
  	u32		Scell_max;
  	u32		max_P;		/* probability, [0 .. 1.0] 32 scaled */
  	/* reciprocal_value(max_P / qth_delta) */
  	struct reciprocal_value	max_P_reciprocal;
  	u32		qth_delta;	/* max_th - min_th */
  	u32		target_min;	/* min_th + 0.4*(max_th - min_th) */
  	u32		target_max;	/* min_th + 0.6*(max_th - min_th) */
  	u8		Scell_log;
  	u8		Wlog;		/* log(W)		*/
  	u8		Plog;		/* random number bits	*/
  	u8		Stab[RED_STAB_SIZE];
  };
  
  struct red_vars {
  	/* Variables */
  	int		qcount;		/* Number of packets since last random
  					   number generation */
  	u32		qR;		/* Cached random number */
  
  	unsigned long	qavg;		/* Average queue length: Wlog scaled */
  	ktime_t		qidlestart;	/* Start of current idle period */
  };
  
  static inline u32 red_maxp(u8 Plog)
  {
  	return Plog < 32 ? (~0U >> Plog) : ~0U;
  }
  
  static inline void red_set_vars(struct red_vars *v)
  {
  	/* Reset average queue length, the value is strictly bound
  	 * to the parameters below, reseting hurts a bit but leaving
  	 * it might result in an unreasonable qavg for a while. --TGR
  	 */
  	v->qavg		= 0;
  
  	v->qcount	= -1;
  }
  
  static inline void red_set_parms(struct red_parms *p,
  				 u32 qth_min, u32 qth_max, u8 Wlog, u8 Plog,
  				 u8 Scell_log, u8 *stab, u32 max_P)
  {
  	int delta = qth_max - qth_min;
  	u32 max_p_delta;
  
  	p->qth_min	= qth_min << Wlog;
  	p->qth_max	= qth_max << Wlog;
  	p->Wlog		= Wlog;
  	p->Plog		= Plog;
  	if (delta < 0)
  		delta = 1;
  	p->qth_delta	= delta;
  	if (!max_P) {
  		max_P = red_maxp(Plog);
  		max_P *= delta; /* max_P = (qth_max - qth_min)/2^Plog */
  	}
  	p->max_P = max_P;
  	max_p_delta = max_P / delta;
  	max_p_delta = max(max_p_delta, 1U);
  	p->max_P_reciprocal  = reciprocal_value(max_p_delta);
  
  	/* RED Adaptative target :
  	 * [min_th + 0.4*(min_th - max_th),
  	 *  min_th + 0.6*(min_th - max_th)].
  	 */
  	delta /= 5;
  	p->target_min = qth_min + 2*delta;
  	p->target_max = qth_min + 3*delta;
  
  	p->Scell_log	= Scell_log;
  	p->Scell_max	= (255 << Scell_log);
  
  	if (stab)
  		memcpy(p->Stab, stab, sizeof(p->Stab));
  }
  
  static inline int red_is_idling(const struct red_vars *v)
  {
  	return v->qidlestart.tv64 != 0;
  }
  
  static inline void red_start_of_idle_period(struct red_vars *v)
  {
  	v->qidlestart = ktime_get();
  }
  
  static inline void red_end_of_idle_period(struct red_vars *v)
  {
  	v->qidlestart.tv64 = 0;
  }
  
  static inline void red_restart(struct red_vars *v)
  {
  	red_end_of_idle_period(v);
  	v->qavg = 0;
  	v->qcount = -1;
  }
  
  static inline unsigned long red_calc_qavg_from_idle_time(const struct red_parms *p,
  							 const struct red_vars *v)
  {
  	s64 delta = ktime_us_delta(ktime_get(), v->qidlestart);
  	long us_idle = min_t(s64, delta, p->Scell_max);
  	int  shift;
  
  	/*
  	 * The problem: ideally, average length queue recalcultion should
  	 * be done over constant clock intervals. This is too expensive, so
  	 * that the calculation is driven by outgoing packets.
  	 * When the queue is idle we have to model this clock by hand.
  	 *
  	 * SF+VJ proposed to "generate":
  	 *
  	 *	m = idletime / (average_pkt_size / bandwidth)
  	 *
  	 * dummy packets as a burst after idle time, i.e.
  	 *
  	 * 	v->qavg *= (1-W)^m
  	 *
  	 * This is an apparently overcomplicated solution (f.e. we have to
  	 * precompute a table to make this calculation in reasonable time)
  	 * I believe that a simpler model may be used here,
  	 * but it is field for experiments.
  	 */
  
  	shift = p->Stab[(us_idle >> p->Scell_log) & RED_STAB_MASK];
  
  	if (shift)
  		return v->qavg >> shift;
  	else {
  		/* Approximate initial part of exponent with linear function:
  		 *
  		 * 	(1-W)^m ~= 1-mW + ...
  		 *
  		 * Seems, it is the best solution to
  		 * problem of too coarse exponent tabulation.
  		 */
  		us_idle = (v->qavg * (u64)us_idle) >> p->Scell_log;
  
  		if (us_idle < (v->qavg >> 1))
  			return v->qavg - us_idle;
  		else
  			return v->qavg >> 1;
  	}
  }
  
  static inline unsigned long red_calc_qavg_no_idle_time(const struct red_parms *p,
  						       const struct red_vars *v,
  						       unsigned int backlog)
  {
  	/*
  	 * NOTE: v->qavg is fixed point number with point at Wlog.
  	 * The formula below is equvalent to floating point
  	 * version:
  	 *
  	 * 	qavg = qavg*(1-W) + backlog*W;
  	 *
  	 * --ANK (980924)
  	 */
  	return v->qavg + (backlog - (v->qavg >> p->Wlog));
  }
  
  static inline unsigned long red_calc_qavg(const struct red_parms *p,
  					  const struct red_vars *v,
  					  unsigned int backlog)
  {
  	if (!red_is_idling(v))
  		return red_calc_qavg_no_idle_time(p, v, backlog);
  	else
  		return red_calc_qavg_from_idle_time(p, v);
  }
  
  
  static inline u32 red_random(const struct red_parms *p)
  {
  	return reciprocal_divide(prandom_u32(), p->max_P_reciprocal);
  }
  
  static inline int red_mark_probability(const struct red_parms *p,
  				       const struct red_vars *v,
  				       unsigned long qavg)
  {
  	/* The formula used below causes questions.
  
  	   OK. qR is random number in the interval
  		(0..1/max_P)*(qth_max-qth_min)
  	   i.e. 0..(2^Plog). If we used floating point
  	   arithmetics, it would be: (2^Plog)*rnd_num,
  	   where rnd_num is less 1.
  
  	   Taking into account, that qavg have fixed
  	   point at Wlog, two lines
  	   below have the following floating point equivalent:
  
  	   max_P*(qavg - qth_min)/(qth_max-qth_min) < rnd/qcount
  
  	   Any questions? --ANK (980924)
  	 */
  	return !(((qavg - p->qth_min) >> p->Wlog) * v->qcount < v->qR);
  }
  
  enum {
  	RED_BELOW_MIN_THRESH,
  	RED_BETWEEN_TRESH,
  	RED_ABOVE_MAX_TRESH,
  };
  
  static inline int red_cmp_thresh(const struct red_parms *p, unsigned long qavg)
  {
  	if (qavg < p->qth_min)
  		return RED_BELOW_MIN_THRESH;
  	else if (qavg >= p->qth_max)
  		return RED_ABOVE_MAX_TRESH;
  	else
  		return RED_BETWEEN_TRESH;
  }
  
  enum {
  	RED_DONT_MARK,
  	RED_PROB_MARK,
  	RED_HARD_MARK,
  };
  
  static inline int red_action(const struct red_parms *p,
  			     struct red_vars *v,
  			     unsigned long qavg)
  {
  	switch (red_cmp_thresh(p, qavg)) {
  		case RED_BELOW_MIN_THRESH:
  			v->qcount = -1;
  			return RED_DONT_MARK;
  
  		case RED_BETWEEN_TRESH:
  			if (++v->qcount) {
  				if (red_mark_probability(p, v, qavg)) {
  					v->qcount = 0;
  					v->qR = red_random(p);
  					return RED_PROB_MARK;
  				}
  			} else
  				v->qR = red_random(p);
  
  			return RED_DONT_MARK;
  
  		case RED_ABOVE_MAX_TRESH:
  			v->qcount = -1;
  			return RED_HARD_MARK;
  	}
  
  	BUG();
  	return RED_DONT_MARK;
  }
  
  static inline void red_adaptative_algo(struct red_parms *p, struct red_vars *v)
  {
  	unsigned long qavg;
  	u32 max_p_delta;
  
  	qavg = v->qavg;
  	if (red_is_idling(v))
  		qavg = red_calc_qavg_from_idle_time(p, v);
  
  	/* v->qavg is fixed point number with point at Wlog */
  	qavg >>= p->Wlog;
  
  	if (qavg > p->target_max && p->max_P <= MAX_P_MAX)
  		p->max_P += MAX_P_ALPHA(p->max_P); /* maxp = maxp + alpha */
  	else if (qavg < p->target_min && p->max_P >= MAX_P_MIN)
  		p->max_P = (p->max_P/10)*9; /* maxp = maxp * Beta */
  
  	max_p_delta = DIV_ROUND_CLOSEST(p->max_P, p->qth_delta);
  	max_p_delta = max(max_p_delta, 1U);
  	p->max_P_reciprocal = reciprocal_value(max_p_delta);
  }
  #endif