typelevel/spire

Error in rational.toDouble

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#660 建立於 2017年12月21日

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 (2 留言) (0 反應) (0 負責人)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

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技術棧
scala
領域
data
議題類型
bug
難度面向新貢獻者的預計實作難度，1 表示很小改動，5 表示專家級工作。
3
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stale
清晰度議題是否清楚說明預期改動、驗收標準和下一步。
clear
前置要求
ScalaSpire libraryrational numbersdouble conversion
新手友善度1-100 的估計分數，表示該議題對首次貢獻者的友善程度。
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.