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Round Half-Even
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| // | |
| // Round Half-Even | |
| // Refer: https://en.wikipedia.org/wiki/Rounding#Round_half_to_even | |
| // Demo: https://codepen.io/schowdhuri/pen/wPXdJe | |
| // | |
| // Author: Subir Chowdhuri | |
| // Updated: 2018-02-12 | |
| // License: MIT | |
| // | |
| // Copyright (c) 2018 Subir Chowdhuri | |
| // | |
| // Permission is hereby granted, free of charge, to any person | |
| // obtaining a copy of this software and associated documentation | |
| // files (the "Software"), to deal in the Software without | |
| // restriction, including without limitation the rights to use, | |
| // copy, modify, merge, publish, distribute, sublicense, and/or sell | |
| // copies of the Software, and to permit persons to whom the | |
| // Software is furnished to do so, subject to the following | |
| // conditions: | |
| // | |
| // The above copyright notice and this permission notice shall be | |
| // included in all copies or substantial portions of the Software. | |
| // | |
| // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, | |
| // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES | |
| // OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND | |
| // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT | |
| // HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, | |
| // WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING | |
| // FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR | |
| // OTHER DEALINGS IN THE SOFTWARE. | |
| // | |
| const isEven = d => d%2===0; | |
| const round = (num, numDecimals=2) => { | |
| if(typeof(num)!=="number") | |
| throw new Error("Unrecognised format"); | |
| if(num < 0) | |
| return -round(-num); | |
| // convert to string; remove trailing 0s | |
| const strNum = `${num}`.replace(/0+$/, ""); | |
| const decimalIndex = strNum.indexOf("."); | |
| if(decimalIndex < 0) // no fractional part | |
| return num; | |
| let intPart = strNum.slice(0, decimalIndex); | |
| if(intPart.length==0) | |
| intPart = 0; | |
| const fractPart = strNum.slice(decimalIndex + 1) // extract fractional part | |
| if(fractPart.length < numDecimals) | |
| return num; | |
| const followingDig = parseInt(fractPart[numDecimals], 10); | |
| if(followingDig < 5) { | |
| // rounding not required | |
| const newFractPart = fractPart.slice(0, numDecimals); | |
| return parseFloat(`${intPart}.${newFractPart}`); | |
| } | |
| if(followingDig === 5) { | |
| const newFractPart = fractPart.slice(0, numDecimals + 1); | |
| if(parseInt(fractPart.slice(numDecimals + 1), 10) > 0) { | |
| fractPart = `${newFractPart}9`; | |
| } else { | |
| fractPart = newFractPart; | |
| } | |
| } | |
| let nextDig = parseInt(fractPart[fractPart.length-1], 10); | |
| let carriedOver = 0; | |
| for(let ptr=fractPart.length-1; ptr>=numDecimals; ptr--) { | |
| let dig = parseInt(fractPart[ptr-1], 10) + carriedOver; | |
| if(nextDig > 5 ||(nextDig==5 && !isEven(dig))) { | |
| ++dig; | |
| } | |
| if(dig > 9) { | |
| dig -= 10; | |
| carriedOver = 1; | |
| } else { | |
| carriedOver = 0; | |
| } | |
| nextDig = dig; | |
| } | |
| let newFractPart = ""; | |
| for(let ptr=numDecimals-2; ptr >=0; ptr--) { | |
| let d = parseInt(fractPart[ptr], 10) + carriedOver; | |
| if(d > 9) { | |
| d -= 10; | |
| carriedOver = 1; | |
| } else { | |
| carriedOver = 0; | |
| } | |
| newFractPart = `${d}${newFractPart}` | |
| } | |
| intPart = parseInt(intPart, 10) + carriedOver; | |
| return parseFloat(`${intPart}.${newFractPart}${nextDig}`); | |
| }; | |
| export default round; |
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