Number Rounding Precision

[tonyvranic]

Hey, I'm writing a Sass interpreter and I found some inconsistencies regarding rounding numbers in practice and the rules in the docs.
My version of Sass is: 1.94.1

The examples in the docs state:

@debug 0.012345678912345; // 0.0123456789
@debug 0.01234567891 == 0.01234567899; // true
@debug 1.00000000009; // 1
@debug 0.99999999991; // 1

But in practice these examples return the following:

@debug 0.012345678912345;  // 0.012345678912345
@debug 0.01234567891 == 0.01234567899; // false
@debug 1.00000000009; // 1.00000000009
@debug 0.99999999991; // 0.99999999991

---

Numbers

Using @debug I couldn't really determine when the rounding even happens, but here are some tests:

// Rounds up to 18 decimal places - The last digit actually changed here on it's own for some reason?
@debug 0.012345678912345678; // 0.012345678912345679
// Doesn't round
@debug 0.000000000000000000000000008; // 0.000000000000000000000000008

When writing SCSS, rounding works by rounding to 10 decimal places:

padding: 0.00000000004px; // padding: 0px;
padding: 0.00000000005px; // padding: 0.0000000001px;

---

Equations

As for equations, they seem to round to 11 decimal places, instead of just going to 10:

@debug 0.000000000014 == 0.000000000014;  // true
@debug 0.000000000014 == 0.000000000015;  // false

---

Integers

And finally rounding to ints:

@debug 1.000000000004 == 1;  // true
@debug 1.000000000005 == 1;  // false

@debug 0.999999999994 == 1;  // false
@debug 0.999999999995 == 1;  // true

[Goodwine]

I believe the behavior is correct as floating point numbers were "recently" updated to follow IEEE. This might be an issue with outdated documentation rather than a bug in the Sass implementation, but I'll double check to verify as I'm not familiar with floating point behavior at those limits

[Goodwine]

By the way, the official website is http://sass-lang.com The linked website sasscss (dot) com isn't official.

[Goodwine]

hm. Maybe it is a bug after all. I guess it depends.. but @debug definitely doesn't truncate or round numbers the way it's documented.

Example (playground):

$var: 0.012345678912345;

x {
  y: $var; // 0.0123456789
}

@debug $var; // 0.012345678912345

[Goodwine]

I think @debug printing the entire number representation ain't a bug. So I think the right way to go about this is to update the documentation to avoid using @debug for the example and adding a note to clarify that @debug will print the entire number without rounding/truncating

[nex3]

That approach sounds good to me. Do you want to make a PR for it?