fix cpm floor issue in price bucket formula #2644
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mkendall07
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May 30, 2018
src/cpmBucketManager.js
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| // force to 10 decimal places to deal with imprecise decimal/binary conversions | ||
| // (for example 0.1 * 3 = 0.30000000000000004) | ||
| cpmTarget = Number(cpmTarget.toFixed(10)); | ||
| return cpmTarget.toFixed(precision); | ||
| } | ||
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| function round(number, precision) { |
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mkendall07
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May 30, 2018
mkendall07
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LGTM
needs 2nd review
Pupis
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to adform/Prebid.js
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Jun 7, 2018
* fix cpm rounding issue in price bucket formula * switch logic to exponent variant instead of precision rounding * update min precision to 2 for exponent * fixed addition
dluxemburg
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to Genius/Prebid.js
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Jul 17, 2018
* fix cpm rounding issue in price bucket formula * switch logic to exponent variant instead of precision rounding * update min precision to 2 for exponent * fixed addition
ghost
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to devunrulymedia/Prebid.js
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Jan 30, 2019
* fix cpm rounding issue in price bucket formula * switch logic to exponent variant instead of precision rounding * update min precision to 2 for exponent * fixed addition
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Type of change
Description of change
To fix the issue reported in #2350
Summary of issue/change (taken from thread in that issue):
The issue appears to be how dividing with decimals is handed in JavaScript. For example, when you divide
4.01 / 0.01in a calculator you would get401. However if you do the same thing in JavaScript (easily see this in the browser console), you get400.99999999999994. There are numerous sets of values that result in this manner, either slightly higher or lower than the expected mark (eg1.11 / .01 = 111.00000000000001).When the
Math.floorgets applied to these low rogue values, it'll reduce it down one level below it's expected value. So400.99999999999994becomes400, which is how we ultimately see a4.01cpm end up in the4.00cpm bucket when we have0.01increments.I've found an adjustment to the formula that appears to work. We multiply the individual values of the formula that gets floored (ie
(cpm - bucketPrice) / incrementby exponential base of 10 (eg100000) to avoid doing the math with decimals which avoids any rounding issues.update - we switched to this alternate logic as it was seen to be more efficient than the previous precision-rounding solution. See https://jsperf.com/cpm-bucket-rounding/ to the unit test comparison.