Fix/IEEE754 decimal precision (#76)

__tests__/algorithm.test.ts

@@ -1,5 +1,7 @@
 import {
+  DECAY,
   default_maximum_interval,
+  FACTOR,
   fsrs,
   FSRS,
   FSRSAlgorithm,
@@ -10,9 +12,6 @@ import {
 } from "../src/fsrs";
 import Decimal from "decimal.js";
 
-const DECAY: number = -0.5;
-const FACTOR: number = 19 / 81;
-
 describe("FACTOR[DECAY = -0.5]", () => {
   it("FACTOR", () => {
     expect(19 / 81).toEqual(new Decimal(19).div(81).toNumber());

package.json

@@ -1,6 +1,6 @@
 {
   "name": "ts-fsrs",
-  "version": "3.5.1",
+  "version": "3.5.2",
   "description": "ts-fsrs is a ES modules package based on TypeScript, used to implement the Free Spaced Repetition Scheduler (FSRS) algorithm. It helps developers apply FSRS to their flashcard applications, there by improving the user learning experience.",
   "main": "dist/index.cjs",
   "module": "dist/index.mjs",

src/fsrs/algorithm.ts

@@ -6,18 +6,21 @@ import type { int } from "./type";
 import { get_fuzz_range } from "./help";
 
 // Ref: https://github.com/open-spaced-repetition/fsrs4anki/wiki/The-Algorithm#fsrs-v4
+export const DECAY: number = -0.5;
+// FACTOR = Math.pow(0.9, 1 / DECAY) - 1
+export const FACTOR: number = 19 / 81;
+
 export class FSRSAlgorithm {
   protected param: FSRSParameters;
   private readonly intervalModifier: number;
   protected seed?: string;
-  private readonly DECAY: number = -0.5;
-  private readonly FACTOR: number = Math.pow(0.9, 1 / this.DECAY) - 1;
 
   constructor(param: Partial<FSRSParameters>) {
     this.param = generatorParameters(param);
     // Ref: https://github.com/open-spaced-repetition/fsrs4anki/wiki/The-Algorithm#fsrs-45
     // The formula used is : I(r,s)= (r^{\frac{1}{DECAY}-1}) \times \frac{s}{FACTOR}
-    this.intervalModifier = (Math.pow(this.param.request_retention, 1 / this.DECAY) - 1) / this.FACTOR;
+    this.intervalModifier =
+      (Math.pow(this.param.request_retention, 1 / DECAY) - 1) / FACTOR;
   }
 
   init_ds(s: SchedulingCard): void {
@@ -94,10 +97,10 @@ export class FSRSAlgorithm {
    * @return {number} Difficulty D \in [1,10]
    */
   init_difficulty(g: Grade): number {
-    return Math.min(
+    return +Math.min(
       Math.max(this.param.w[4] - (g - 3) * this.param.w[5], 1),
       10,
-    );
+    ).toFixed(8);
   }
 
   /**
@@ -160,7 +163,7 @@ export class FSRSAlgorithm {
    * @param {number} difficulty D \in [1,10]
    */
   constrain_difficulty(difficulty: number): number {
-    return Math.min(Math.max(Number(difficulty.toFixed(2)), 1), 10);
+    return Math.min(Math.max(+difficulty.toFixed(8), 1), 10);
   }
 
   /**
@@ -171,7 +174,9 @@ export class FSRSAlgorithm {
    * @return {number} difficulty
    */
   mean_reversion(init: number, current: number): number {
-    return this.param.w[7] * init + (1 - this.param.w[7]) * current;
+    return +(this.param.w[7] * init + (1 - this.param.w[7]) * current).toFixed(
+      8,
+    );
   }
 
   /**
@@ -186,7 +191,7 @@ export class FSRSAlgorithm {
   next_recall_stability(d: number, s: number, r: number, g: Grade): number {
     const hard_penalty = Rating.Hard === g ? this.param.w[15] : 1;
     const easy_bound = Rating.Easy === g ? this.param.w[16] : 1;
-    return (
+    return +(
       s *
       (1 +
         Math.exp(this.param.w[8]) *
@@ -195,7 +200,7 @@ export class FSRSAlgorithm {
           (Math.exp((1 - r) * this.param.w[10]) - 1) *
           hard_penalty *
           easy_bound)
-    );
+    ).toFixed(8);
   }
 
   /**
@@ -207,12 +212,12 @@ export class FSRSAlgorithm {
    * @return {number} S^\prime_f new stability after forgetting
    */
   next_forget_stability(d: number, s: number, r: number): number {
-    return Number((
+    return +(
       this.param.w[11] *
       Math.pow(d, -this.param.w[12]) *
       (Math.pow(s + 1, this.param.w[13]) - 1) *
       Math.exp((1 - r) * this.param.w[14])
-    ).toFixed(2));
+    ).toFixed(8);
   }
 
   /**
@@ -223,6 +228,6 @@ export class FSRSAlgorithm {
    * @return {number} r Retrievability (probability of recall)
    */
   forgetting_curve(elapsed_days: number, stability: number): number {
-    return Math.pow(1 + this.FACTOR * elapsed_days / stability, this.DECAY);
+    return +Math.pow(1 + (FACTOR * elapsed_days) / stability, DECAY).toFixed(8);
   }
 }

src/fsrs/default.ts

@@ -9,7 +9,7 @@ export const default_w = [
 ];
 export const default_enable_fuzz = false;
 
-export const FSRSVersion: string = "3.5.1";
+export const FSRSVersion: string = "3.5.2";
 
 export const generatorParameters = (
   props?: Partial<FSRSParameters>,