popularityCalc.hpp

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#pragma once
 
#define MINUTE 60.0
#define HOUR   (60.0 * MINUTE)
#define DAY    (24.0 * HOUR)
#define WEEK   (7.0 * DAY)
 
/* popularity calculation
 * y[n] = MULTIPLIER * x / DAMPING + (1.0 - 1.0 / DAMPING) * y[n-1]
 * where x is file usage frequency
 */
#define START_DAMPING            50000.0
#define DAMPING                  1000000.0
#define MULTIPLIER               3600.0
#define REACH_FULL_DAMPING_AFTER (1.0 * WEEK)
#define SLOPE                    ((DAMPING - START_DAMPING) / REACH_FULL_DAMPING_AFTER)
/* DAMPING is how slowly popularity changes.
 * MULTIPLIER is to scale values to accesses per hour.
 */
 
#define AVG_USAGE 0.238 // 40hr/(7days * 24hr/day)
/* for calculating initial popularity for new files
 * Unit: accesses per second.
 */