Fix integer parsing

[nrabulinski]

This Pull Request makes it possible to continue with #1602 and also fixes some errors with parsing integers.

It changes the following:

• Instead of manually parsing and adding each character I use i128::from_str_radix, which is then converted to f64

Unanswered questions:

- What does the spec say about even larger numbers? I've tested NodeJS and Firefox and you can more or less get unlimited range, albeit anything that's larger than Number.MAX_SAFE_INTEGER is not represented exactly. With this solution, however, numbers get clamped to -1.7e+38 and 1.7e+38. I'm assuming fixing this would most likely require an overhaul of the number representation and parsing code.

[jedel1043]

• What does the spec say about even larger numbers? I've tested NodeJS and Firefox and you can more or less get unlimited range, albeit anything that's larger than Number.MAX_SAFE_INTEGER is not represented exactly. With this solution, however, numbers get clamped to -1.7e+38 and 1.7e+38. I'm assuming fixing this would most likely require an overhaul of the number representation and parsing code.

Now that I think about it, couldn't we use JsBigInt to parse the string as a big int, then convert into an f64? JsBigInt already has to_f64 and from_string_radix, so it should be an easy change.

[nrabulinski]

Disregard my previous comment, I got confused 😄 but yes, we probably could use BigInt for that, should I look into this?

[jedel1043]

Disregard my previous comment, I got confused 😄 but yes, we probably could use BigInt for that, should I look into this?

Please do!

[nrabulinski]

Please do!

It seems to work correctly!

[jedel1043]

Looks good to me! :D

[raskad]

Test262 conformance changes:

Test result	master count	PR count	difference
Total	80,930	80,930	0
Passed	33,313	33,317	+4
Ignored	15,898	15,898	0
Failed	31,719	31,715	-4
Panics	0	0	0
Conformance	41.16%	41.17%	+0.00%

Fixed tests (4):

test/built-ins/Number/prototype/toFixed/exactness.js [strict mode] (previously Failed)
test/built-ins/Number/prototype/toFixed/exactness.js (previously Failed)
test/built-ins/parseInt/S15.1.2.2_A7.2_T3.js [strict mode] (previously Failed)
test/built-ins/parseInt/S15.1.2.2_A7.2_T3.js (previously Failed)