I’m trying to multiply some small numbers in PHP, but bcmul is returning zero because the float value is being turned into scientific notation.
I tried using sprintf('%.32f',$value)
on the small float values, but since the number of decimal places is unknown, it gets the wrong rounding, and then it’ll cause rounding errors when multiplying.
Also, I can’t use strpos('e',$value)
to find out if it’s scientific notation number, because it doesn’t finds it even if I cast it as a string with (string)$value
Here’s some example code:
$value = (float)'7.4e-5'; // This number comes from an API like this $value2 = (float)3.65; // Another number from API echo bcmul($value,$value2); // 0
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Answer
Okay, I found a way to solve it, so, here’s how to multiply very small floating point numbers without needing to set an explicit scale for the numbers:
function getDecimalPlaces($value) { // first we get how many decimal places the small number has // this code was gotten on another StackOverflow answer $current = $value - floor($value); for ($decimals = 0; ceil($current); $decimals++) { $current = ($value * pow(10, $decimals + 1)) - floor($value * pow(10, $decimals + 1)); } return $decimals; } function multiplySmallNumbers($value, $smallvalue) { $decimals = getDecimalPlaces($smallvalue); // Then we get number of decimals on it $smallvalue = sprintf('%.'.$decimals.'f',$smallvalue ); // Since bcmul uses the float values as strings, we get the number as a string with the correct number of zeroes return (bcmul($value,$smallvalue)); }