Error in rational.toDouble · typelevel/spire#660

(2 评论) (0 反应) (0 负责人)Scala (1,775 star) (238 fork)batch import

bughelp wantedlow hanging fruit

描述

The toDouble method on Rational instances returns incorrectly for certain inputs. To reproduce,

import spire.math.Rational

def bld(numStr: String, denomStr: String): (Double, Double) = {
  val num = BigInt(numStr)
  val denom = BigInt(denomStr)

  val expected = (BigDecimal(num) / BigDecimal(denom)).toDouble
  val actual = Rational(num, denom).toDouble

  (expected, actual)
}

println(
  bld(
    "179709322496314735297382168733437804616092100361307360024524978382010425322923559",
    "179709322496314735297382168733483632988275016201074155389238170380281177201180672"
  ))
println(
  bld(
    "-1257965257474203147081675181125850088132776039278857905825424935347911159685302509",
    "1257965257474203147081675181134385430917925113407519087724667192661968240408264704"
  ))
println(bld(
  "3618502788666131106986593281458997943466459808578940660043329292438660832363",
  "3618502788666131106986593281521497120414687020801267626233049500247285301248"
))

spire version: 0.14.1 scala version: 2.12.4 javac: 1.8.0_152 jvm: Java HotSpot(TM) 64-Bit Server VM (build 25.152-b16, mixed mode) OS: Ubuntu 16.04

贡献者指南

技术栈: scala
领域: data
议题类型: bug
难度: 3
预计时间: 1-3 hours
活动状态: stale
清晰度: clear
前置要求: ScalaSpire libraryrational numbersdouble conversion
新手友好度: 50
研究方向: Investigate the toDouble method in spire.math.Rational. The issue provides reproduction code. Check the implementation of toDouble for large numerator/denominator causing precision loss. Look at the Rational.scala file in the spire source.