EDIT:
Converted to using round which returns a float
I am converting am rounding a number to 2 decimals using round function
My question is about this line of code below:
Could their be rounding errors or unexpected behavior that could cause this condition to be true when it should not be?
if ($cc_amount > $total)
FULL CODE:
$cc_amount = round($this->sale_lib->get_payment_total('credit'),2);
$total = round($this->sale_lib->get_total(),2);
//Since they are floats could there be rounding errors?
if ($cc_amount > $total)
{
$this->_reload(array('error' => 'Credit card payment is greater than total');
}
It's a little confusing as to what you are doing.
When comparing strings it could grab each character's ascii code and compare them one at a time from the left most character to the right so something like 823 > 2015.
If I were to compare I'd keep them in number format and calculate each amount given approximately like so.
function to_decimals($number, $decimals = 2)
{
if (is_numeric($number))
{
$updown = (10^$decimals)
return round(($number * $updown))/$updown;
}
else
{
return -999999;
}
}
Related
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,$value2); // 0
By default the bc-functions round to 0 decimals. You can change this behavior by either using bcscale or by by changing the bcmath.scale value in your php.ini.
Okay, I found a way to solve it, so, here's how to multiply very small floating point numbers without needing to set an explicit scale for the numbers:
function getDecimalPlaces($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));
}
I have to validate if a float number has maximum two digits.
I've tried a lot of methods but all fails in more or lase cases.
Last of them were:
//fails for 2638655.99
private function hasMoreThanTwoDecimals(string $number): bool
{
$number = abs($number);
$intPart = floor($number);
$floatPart = $number - $intPart;
return (strlen($floatPart) > 4);
}
OR
//fails for 36.62
private function hasMoreThanTwoDecimals(string $number): bool
{
return $number * 100 - floor($number * 100) > 0.00001;
}
What other methods do you use?
You can't determine the exact number of decimals with the float datatype, because the internal representation is binary. In binary, fx. 0.1 can not be represented exactly. That's why loops always should have integer increments.
for ($i = -1; $i < 1; $i += 0.1) {
if ($i == 0) {
echo "Zero is here!";
}
}
will never say "Zero is here!" because of binary rounding issues.
Using an Epsilon
You already tried to use an epsilon (a very small value) for thesholding (here a refactored version of your function):
private function hasMoreThanTwoDecimals(string $number): bool
{
$epsilon = 0.00001;
return fmod($number * 100, 1.0) > $epsilon;
}
but fails for some values. In that case, you need to increase your epsilon value.
String Arithmetic
The more precise way is to avoid float and use string representations instead. This is your best option, since - according to your function signature - your numbers are represented as strings already.
private function hasMoreThanTwoDecimals(string $number): bool
{
return bcmod(bcmul($number, '100'), '1.0') != 0;
}
This needs the BCMath module to be included in your PHP. A package supporting BCMath and other solutions is brick/math.
The Cheap Solution
However, if you really just need to probe the number and not are doing calculations, you can get the desired result with pattern matching using preg_match.
private function hasMoreThanTwoDecimals(string $number): bool
{
// Trailing 0 does not add to number of decimals
$number = rtrim($number, '0');
return preg_match('~\.\d\d\d~', $number);
}
You can explode the number using the . delimeter, then you return the length of the second part :
$num = 2638655.99;
echo strlen(explode('.',$num)[1]); // Echo 2
Taking the question literally, if a binary floating point number has a maximum of two decimal digits after the decimal point, the fractional part must be one of .0, .25, .5, or .75.
All other binary floating point numbers really have more decimal digits, although printout formatting may hide them. For example, the closest IEEE 754 64-bit binary number to 2638655.99 is 2638655.99000000022351741790771484375, which has more than two digits after the decimal point.
You could subtract the integer part and then test for the remainder being one of the four possibilities.
Alternatively, the real question may be how to determine whether displaying the number will show no more than two digits after the decimal point. If so, convert to string using the appropriate method, then locate the decimal point and count the digits after it, for example as suggested in this answer.
$res = preg_match("^[+-]?([0]{1}|[1-9]{1}[0-9]*)(\.?[0-9]{1,2})?$", $num) == true;
would be the best solution in my opinion. You can use signs (optional) and enforce that a number starts with only one zero.
Possible:
+0.10
+123.01
-1
123
Not possible:
00.0
0001.0
1.
123.123
Be aware that preg_match returns 0 if no match is found and false if an error occurred (preg_match)
you can use the number_format
number_format($number, 2, '.', '');
I got a problem with this script
$total = 0;
$expected_total = 1111;
$i = [85.46,85.46,85.46,85.46,85.46,85.46,85.46,85.46,85.46,85.46,85.46,85.46,85.48];
foreach ($i as $item) { $total += $item; }
if($total != $expected_total) {
echo json_encode([$total,$expected_total]);
}
The problem is that at the end of the sum the $total should be equal to the $expected_total.
I thought about different number types, I printed the type of the two vars and I was right, one was double and the other was integer, so I converted the integer to double
$expected_total = 1111.00;
but the result is still the same.
The only solution that I could find was comparing the rappresentation of the two numbers, casting them to a string.
if((string)$total != (string)$expected_total) {
echo json_encode([$total,$expected_total]);
}
But obviously this is kind of a hack.
Have you ever had a similar problem? How have you solved it?
PHP version : 5.5.9
Many Thanks
This is not only PHP problem. It is about representation of floating point numbers in memory. Floating numbers has limited precision. PHP uses IEEE 754. Read carefully the manual page and you will understand.
You can find in manual code snippet of how to do it.
$a = 1.23456789;
$b = 1.23456780;
$epsilon = 0.00001; //very small number
if(abs($a-$b) < $epsilon) {
echo "true";
}
If you want to check them as integers you could round both values.
You should change the if-statement to the following:
if(round($total) != round($expected_total)) {
echo json_encode([$total,$expected_total]);
}
If you do it like this you will compare the rounded values, which will be the same.
There is a big red label in the PHP Manual, that says:
Floating point numbers have limited precision…
So never trust floating number results to the last digit, and do not compare floating point numbers directly for equality. If higher precision is necessary, the arbitrary precision math functions and gmp functions are available.
In this specific case, you could add the floating numbers using bcadd() and compare the totals using bccomp(). Both functions are provided by the BC Math extension:
foreach ($i as $item) {
$total = bcadd((string) $total, (string) $item, 2);
}
if (bccomp((string) $total, (string) $expected_total, 2) == 0) {
echo json_encode([$total,$expected_total]);
}
MySQL data imoprt mongo database.
price float(15,2) in mysql, mongo is not float(15,2).
I want to Determine a var $price have two decimal places.
eg. 100.00 is right, 100 or 100.0 is wrong.
eg.1
$price = 100.00;
$price have two decimal, it's right.
eg.2
$price = 100.0;
$price have not two decimal, it's wrong.
I like to use Regular Expressions to do these things
function validateTwoDecimals($number)
{
if(preg_match('/^[0-9]+\.[0-9]{2}$/', $number))
return true;
else
return false;
}
(Thanks to Fred-ii- for the corrections)
Everybody is dancing around the fact that floating point numbers don't have a number of decimal places in their internal representation. i.e. in float 100 == 100.0 == 100.00 == 100.000 and are all represented by the same number, effectively 100 and is stored that way.
The number of decimal places in this example only has a context when the number is represented as a string. In which case any string function that counts the number of digits trailing the decimal point could be used to check.
number_format($price, $numberOfDecimalDigits) === $price;
or
strrpos($price, '.') === strlen($price) - 1 - $numberOfDecimalDigits;
Trivia: $price should not be called a "float variable". This is a string that happens to represent a float value. 100.00 as a float has zero decimal digits, and 100.00 === 100 as float :
$price = 100.00;
echo $price; // output: 100
$price2 = (float)100;
echo $price === $price2; // ouput: 1
In order for this to work, the number will need to be wrapped in quotes.
With the many scripts I've tested, using $price = 100.00; without quotes did not work, while $price = 100.10; did, so this is as best as it gets.
<?php
$number = '100.00';
echo $number.'<br>';
$count = explode('.',$number);
echo 'The number of digits after the decimal point is: ' . strlen($count[1]);
if(strlen($count[1]) == 2){
echo "<br>";
echo "There is 2 decimal points.";
}
else{
echo "<br>";
echo "There is not 2 decimal points.";
}
After you format the value, you can check with simply splitting the value as string into 2 parts, for example with explode ...
$ex=explode('.',$in,2); if (strlen($ex[1])==2)
{
// true
}
else
{
// false
}
But again, as i've commented already, if you really have floating input, this is just not a reliable way, as floating numbers are without set decimal places, even if they appears so because of the rounding at the float=>string conversion
What you can do, if you really have floating numbers and wish to have xxx.yy format numbers:
1) convert float to string using round($x,2), so it will round to 2 decimal places.
2) explode the number as i've described, and do the following:
while (strlen($ex[1]<2)) {$ex[1].='0';}
$number=implode('.',$ex);
I would use the following function for that:
function isFloatWith2Decimals($number) {
return (bool) preg_match('/^(?:[1-9]{1}\d*|0)\.\d{2}$/', $number);
}
This will also check if you have only one leading 0 so number like 010.23 won't be considered as valid whereas number like 0.23 will.
And if you don't care about leading 0 you could use simpler method:
function isFloatWith2Decimals($number) {
return (bool) preg_match('/^\d+\.\d{2}$/', $number);
}
Of course numbers need to be passed as string - if you pass 100.00 won't be considered as true, whereas '100.00' will
I have two variables in a PHP program for billing statements, $charges and $payments.
$charges is the total amount due before any payments. $payments is the total amount received.
I calculate the balance due like so:
$balance_due = $charges-$payments;
Simple, except I am getting the following result:
$balance_due has -9.0949470177293E-13 for a value (expecting 0).
Both $charges and $payments have a value of 5511.53.
When I var_dump($charges) and var_dump($payments) they both show: float(5511.53)
This code (and === ):
if($charges == $payments){
error_log('they are the same');
}else{
error_log('they are not the same');
}
both result in false.
If I hard code: $charges = $payments = 5511.53; and run it then $balance_due = 0 as expected.
I am confused. What am I missing?
EDIT NOTES
I was able to use a user contributed function by Nitrogen found on the BC Math Functions page that was suggested I look at in order to come up with the following solution:
if(Comp($charges, $payments)===0){
$balance_due = 0;
}else{
$balance_due = ( $charges - $payments );
}
function Comp($Num1,$Num2,$Scale=null) {
// check if they're valid positive numbers, extract the whole numbers and decimals
if(!preg_match("/^\+?(\d+)(\.\d+)?$/",$Num1,$Tmp1)||
!preg_match("/^\+?(\d+)(\.\d+)?$/",$Num2,$Tmp2)) return('0');
// remove leading zeroes from whole numbers
$Num1=ltrim($Tmp1[1],'0');
$Num2=ltrim($Tmp2[1],'0');
// first, we can just check the lengths of the numbers, this can help save processing time
// if $Num1 is longer than $Num2, return 1.. vice versa with the next step.
if(strlen($Num1)>strlen($Num2)) return(1);
else {
if(strlen($Num1)<strlen($Num2)) return(-1);
// if the two numbers are of equal length, we check digit-by-digit
else {
// remove ending zeroes from decimals and remove point
$Dec1=isset($Tmp1[2])?rtrim(substr($Tmp1[2],1),'0'):'';
$Dec2=isset($Tmp2[2])?rtrim(substr($Tmp2[2],1),'0'):'';
// if the user defined $Scale, then make sure we use that only
if($Scale!=null) {
$Dec1=substr($Dec1,0,$Scale);
$Dec2=substr($Dec2,0,$Scale);
}
// calculate the longest length of decimals
$DLen=max(strlen($Dec1),strlen($Dec2));
// append the padded decimals onto the end of the whole numbers
$Num1.=str_pad($Dec1,$DLen,'0');
$Num2.=str_pad($Dec2,$DLen,'0');
// check digit-by-digit, if they have a difference, return 1 or -1 (greater/lower than)
for($i=0;$i<strlen($Num1);$i++) {
if((int)$Num1{$i}>(int)$Num2{$i}) return(1);
else
if((int)$Num1{$i}<(int)$Num2{$i}) return(-1);
}
// if the two numbers have no difference (they're the same).. return 0
return(0);
}
}
}
That solution worked for me. The answer provided by imtheman below also works and seems more efficient so I am going to use that one instead. Is there any reason not to use one or the other of these?
The way I solved this problem when I ran into it was using php's number_format(). From php documentation:
string number_format(float $number [, int $decimals = 0 ])
So what I would do is this:
$balance_due = number_format($charges-$payments, 2);
And that should solve your problem.
Note: number_format() will return a string, so to compare it you must use == (not ===) or cast it back into a (float) before comparison.