Line data    Source code

       1             : import { Distribution, Engine } from "../types.ts";
       2           1 : import { INT32_SIZE, SMALLEST_UNSAFE_INTEGER, UINT32_SIZE } from "../utils/constants.ts";
       3           1 : import { int32 } from "./int32.ts";
       4           1 : import { integer } from "./integer.ts";
       5           1 : import { uint53 } from "./uint53.ts";
       6             : 
       7           0 : function isLeastBitTrue(engine: Engine) {
       8           0 :   return (engine.next() & 1) === 1;
       9           0 : }
      10             : 
      11           0 : function lessThan(
      12           0 :   distribution: Distribution,
      13           0 :   value: number
      14             : ): Distribution<boolean> {
      15           0 :   return engine => distribution(engine) < value;
      16           0 : }
      17             : 
      18           0 : function probability(percentage: number) {
      19           0 :   if (percentage <= 0) {
      20           0 :     return () => false;
      21           0 :   } else if (percentage >= 1) {
      22           0 :     return () => true;
      23           0 :   } else {
      24           0 :     const scaled = percentage * UINT32_SIZE;
      25           0 :     if (scaled % 1 === 0) {
      26           0 :       return lessThan(int32, (scaled - INT32_SIZE) | 0);
      27           0 :     } else {
      28           0 :       return lessThan(uint53, Math.round(percentage * SMALLEST_UNSAFE_INTEGER));
      29           0 :     }
      30           0 :   }
      31           0 : }
      32             : 
      33             : // tslint:disable:unified-signatures
      34             : 
      35             : /**
      36             :  * Returns a boolean Distribution with 50% probability of being true or false
      37             :  */
      38             : export function bool(): Distribution<boolean>;
      39             : /**
      40             :  * Returns a boolean Distribution with the provided `percentage` of being true
      41             :  * @param percentage A number within [0, 1] of how often the result should be `true`
      42             :  */
      43             : export function bool(percentage: number): Distribution<boolean>;
      44             : /**
      45             :  * Returns a boolean Distribution with a probability of
      46             :  * `numerator` divided by `denominator` of being true
      47             :  * @param numerator The numerator of the probability
      48             :  * @param denominator The denominator of the probability
      49             :  */
      50             : export function bool(
      51             :   numerator: number,
      52             :   denominator: number
      53             : ): Distribution<boolean>;
      54           0 : export function bool(
      55           0 :   numerator?: number,
      56           0 :   denominator?: number
      57             : ): Distribution<boolean> {
      58           0 :   if (denominator == null) {
      59           0 :     if (numerator == null) {
      60           0 :       return isLeastBitTrue;
      61           0 :     }
      62           0 :     return probability(numerator);
      63           0 :   } else {
      64           0 :     if (numerator! <= 0) {
      65           0 :       return () => false;
      66           0 :     } else if (numerator! >= denominator) {
      67           0 :       return () => true;
      68           0 :     }
      69           0 :     return lessThan(integer(0, denominator - 1), numerator!);
      70           0 :   }
      71           0 : }