Fix/stability not restrict maximun and minimun (#126)

__tests__/FSRSV5.test.ts

@@ -166,7 +166,7 @@ describe('get retrievability', () => {
     let card = createEmptyCard()
     let now = new Date()
     let i = 0
-    while (i < 10 ** 3) {
+    while (i < 5) {
       card = fsrs.next(card, now, Rating.Again).card
       now = card.due
       i++

package.json

@@ -1,6 +1,6 @@
 {
   "name": "ts-fsrs",
-  "version": "4.3.0",
+  "version": "4.3.1",
   "description": "ts-fsrs is a versatile package based on TypeScript that supports ES modules, CommonJS, and UMD. It implements the Free Spaced Repetition Scheduler (FSRS) algorithm, enabling developers to integrate FSRS into their flashcard applications to enhance the user learning experience.",
   "main": "dist/index.cjs",
   "umd": "dist/index.umd.js",

src/fsrs/algorithm.ts

@@ -1,7 +1,7 @@
 import { generatorParameters } from './default'
 import { FSRSParameters, Grade, Rating } from './models'
 import type { int } from './types'
-import { get_fuzz_range } from './help'
+import { clamp, get_fuzz_range } from './help'
 import { alea } from './alea'
 
 /**
@@ -213,15 +213,17 @@ 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 +clamp(
       s *
-      (1 +
-        Math.exp(this.param.w[8]) *
-          (11 - d) *
-          Math.pow(s, -this.param.w[9]) *
-          (Math.exp((1 - r) * this.param.w[10]) - 1) *
-          hard_penalty *
-          easy_bound)
+        (1 +
+          Math.exp(this.param.w[8]) *
+            (11 - d) *
+            Math.pow(s, -this.param.w[9]) *
+            (Math.exp((1 - r) * this.param.w[10]) - 1) *
+            hard_penalty *
+            easy_bound),
+      0.01,
+      36500.0
     ).toFixed(8)
   }
 
@@ -234,11 +236,13 @@ export class FSRSAlgorithm {
    * @return {number} S^\prime_f new stability after forgetting
    */
   next_forget_stability(d: number, s: number, r: number): number {
-    return +(
+    return +clamp(
       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])
+        Math.pow(d, -this.param.w[12]) *
+        (Math.pow(s + 1, this.param.w[13]) - 1) *
+        Math.exp((1 - r) * this.param.w[14]),
+      0.01,
+      36500.0
     ).toFixed(8)
   }
 
@@ -249,8 +253,10 @@ export class FSRSAlgorithm {
    * @param {Grade} g Grade (Rating[0.again,1.hard,2.good,3.easy])
    */
   next_short_term_stability(s: number, g: Grade): number {
-    return +(
-      s * Math.exp(this.param.w[17] * (g - 3 + this.param.w[18]))
+    return +clamp(
+      s * Math.exp(this.param.w[17] * (g - 3 + this.param.w[18])),
+      0.01,
+      36500.0
     ).toFixed(8)
   }
 

src/fsrs/default.ts

@@ -11,7 +11,7 @@ export const default_w = [
 export const default_enable_fuzz = false
 export const default_enable_short_term = true
 
-export const FSRSVersion: string = 'v4.3.0 using FSRS V5.0'
+export const FSRSVersion: string = 'v4.3.1 using FSRS V5.0'
 
 export const generatorParameters = (
   props?: Partial<FSRSParameters>

src/fsrs/help.ts

@@ -187,3 +187,7 @@ export function get_fuzz_range(
   min_ivl = Math.min(min_ivl, max_ivl)
   return { min_ivl, max_ivl }
 }
+
+export function clamp(value: number, min: number, max: number): number {
+  return Math.min(Math.max(value, min), max)
+}