boa/boa/src/builtins/number/mod.rs

//! This module implements the global `Number` object.
//!
//! The `Number` JavaScript object is a wrapper object allowing you to work with numerical values.
//! A `Number` object is created using the `Number()` constructor. A primitive type object number is created using the `Number()` **function**.
//!
//! The JavaScript `Number` type is double-precision 64-bit binary format IEEE 754 value. In more recent implementations,
//! JavaScript also supports integers with arbitrary precision using the BigInt type.
//!
//! More information:
//!  - [ECMAScript reference][spec]
//!  - [MDN documentation][mdn]
//!
//! [spec]: https://tc39.es/ecma262/#sec-number-object
//! [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number

use super::function::make_builtin_fn;
use crate::{
    builtins::BuiltIn,
    object::{ConstructorBuilder, ObjectData},
    property::Attribute,
    value::{AbstractRelation, IntegerOrInfinity, Value},
    BoaProfiler, Context, Result,
};
use num_traits::{float::FloatCore, Num};

mod conversions;

pub(crate) use conversions::{f64_to_int32, f64_to_uint32};

#[cfg(test)]
mod tests;

const BUF_SIZE: usize = 2200;

/// `Number` implementation.
#[derive(Debug, Clone, Copy)]
pub(crate) struct Number;

/// Maximum number of arguments expected to the builtin parseInt() function.
const PARSE_INT_MAX_ARG_COUNT: usize = 2;

/// Maximum number of arguments expected to the builtin parseFloat() function.
const PARSE_FLOAT_MAX_ARG_COUNT: usize = 1;

impl BuiltIn for Number {
    const NAME: &'static str = "Number";

    fn attribute() -> Attribute {
        Attribute::WRITABLE | Attribute::NON_ENUMERABLE | Attribute::CONFIGURABLE
    }

    fn init(context: &mut Context) -> (&'static str, Value, Attribute) {
        let _timer = BoaProfiler::global().start_event(Self::NAME, "init");

        let attribute = Attribute::READONLY | Attribute::NON_ENUMERABLE | Attribute::PERMANENT;
        let number_object = ConstructorBuilder::with_standard_object(
            context,
            Self::constructor,
            context.standard_objects().number_object().clone(),
        )
        .name(Self::NAME)
        .length(Self::LENGTH)
        .static_property("EPSILON", f64::EPSILON, attribute)
        .static_property("MAX_SAFE_INTEGER", Self::MAX_SAFE_INTEGER, attribute)
        .static_property("MIN_SAFE_INTEGER", Self::MIN_SAFE_INTEGER, attribute)
        .static_property("MAX_VALUE", Self::MAX_VALUE, attribute)
        .static_property("MIN_VALUE", Self::MIN_VALUE, attribute)
        .static_property("NEGATIVE_INFINITY", f64::NEG_INFINITY, attribute)
        .static_property("POSITIVE_INFINITY", f64::INFINITY, attribute)
        .static_property("NaN", f64::NAN, attribute)
        .method(Self::to_exponential, "toExponential", 1)
        .method(Self::to_fixed, "toFixed", 1)
        .method(Self::to_locale_string, "toLocaleString", 0)
        .method(Self::to_precision, "toPrecision", 1)
        .method(Self::to_string, "toString", 1)
        .method(Self::value_of, "valueOf", 0)
        .static_method(Self::number_is_finite, "isFinite", 1)
        .static_method(Self::number_is_nan, "isNaN", 1)
        .static_method(Self::is_safe_integer, "isSafeInteger", 1)
        .static_method(Self::number_is_integer, "isInteger", 1)
        .build();

        let global = context.global_object().clone();
        make_builtin_fn(
            Self::parse_int,
            "parseInt",
            &global,
            PARSE_INT_MAX_ARG_COUNT,
            context,
        );
        make_builtin_fn(
            Self::parse_float,
            "parseFloat",
            &global,
            PARSE_FLOAT_MAX_ARG_COUNT,
            context,
        );
        make_builtin_fn(Self::global_is_finite, "isFinite", &global, 1, context);
        make_builtin_fn(Self::global_is_nan, "isNaN", &global, 1, context);

        (Self::NAME, number_object.into(), Self::attribute())
    }
}

impl Number {
    /// The amount of arguments this function object takes.
    pub(crate) const LENGTH: usize = 1;

    /// The `Number.MAX_SAFE_INTEGER` constant represents the maximum safe integer in JavaScript (`2^53 - 1`).
    ///
    /// /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-number.max_safe_integer
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_SAFE_INTEGER
    pub(crate) const MAX_SAFE_INTEGER: f64 = 9_007_199_254_740_991_f64;

    /// The `Number.MIN_SAFE_INTEGER` constant represents the minimum safe integer in JavaScript (`-(253 - 1)`).
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-number.min_safe_integer
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MIN_SAFE_INTEGER
    pub(crate) const MIN_SAFE_INTEGER: f64 = -9_007_199_254_740_991_f64;

    /// The `Number.MAX_VALUE` property represents the maximum numeric value representable in JavaScript.
    ///
    /// The `MAX_VALUE` property has a value of approximately `1.79E+308`, or `2^1024`.
    /// Values larger than `MAX_VALUE` are represented as `Infinity`.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-number.max_value
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_VALUE
    pub(crate) const MAX_VALUE: f64 = f64::MAX;

    /// The `Number.MIN_VALUE` property represents the smallest positive numeric value representable in JavaScript.
    ///
    /// The `MIN_VALUE` property is the number closest to `0`, not the most negative number, that JavaScript can represent.
    /// It has a value of approximately `5e-324`. Values smaller than `MIN_VALUE` ("underflow values") are converted to `0`.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-number.min_value
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MIN_VALUE
    pub(crate) const MIN_VALUE: f64 = f64::MIN;

    /// `Number( value )`
    pub(crate) fn constructor(
        this: &Value,
        args: &[Value],
        context: &mut Context,
    ) -> Result<Value> {
        let data = match args.get(0) {
            Some(ref value) => value.to_numeric_number(context)?,
            None => 0.0,
        };
        this.set_data(ObjectData::Number(data));

        Ok(Value::from(data))
    }

    /// This function returns a `Result` of the number `Value`.
    ///
    /// If the `Value` is a `Number` primitive of `Number` object the number is returned.
    /// Otherwise an `TypeError` is thrown.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-thisnumbervalue
    fn this_number_value(value: &Value, context: &mut Context) -> Result<f64> {
        match *value {
            Value::Integer(integer) => return Ok(f64::from(integer)),
            Value::Rational(rational) => return Ok(rational),
            Value::Object(ref object) => {
                if let Some(number) = object.borrow().as_number() {
                    return Ok(number);
                }
            }
            _ => {}
        }

        Err(context.construct_type_error("'this' is not a number"))
    }

    /// Helper function that formats a float as a ES6-style exponential number string.
    fn num_to_exponential(n: f64) -> String {
        match n.abs() {
            x if x > 1.0 => format!("{:e}", n).replace("e", "e+"),
            x if x == 0.0 => format!("{:e}", n).replace("e", "e+"),
            _ => format!("{:e}", n),
        }
    }

    /// `Number.prototype.toExponential( [fractionDigits] )`
    ///
    /// The `toExponential()` method returns a string representing the Number object in exponential notation.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-number.prototype.toexponential
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toExponential
    #[allow(clippy::wrong_self_convention)]
    pub(crate) fn to_exponential(
        this: &Value,
        _: &[Value],
        context: &mut Context,
    ) -> Result<Value> {
        let this_num = Self::this_number_value(this, context)?;
        let this_str_num = Self::num_to_exponential(this_num);
        Ok(Value::from(this_str_num))
    }

    /// `Number.prototype.toFixed( [digits] )`
    ///
    /// The `toFixed()` method formats a number using fixed-point notation
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-number.prototype.tofixed
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toFixed
    #[allow(clippy::wrong_self_convention)]
    pub(crate) fn to_fixed(this: &Value, args: &[Value], context: &mut Context) -> Result<Value> {
        let this_num = Self::this_number_value(this, context)?;
        let precision = match args.get(0) {
            Some(n) => match n.to_integer(context)? as i32 {
                x if x > 0 => n.to_integer(context)? as usize,
                _ => 0,
            },
            None => 0,
        };
        let this_fixed_num = format!("{:.*}", precision, this_num);
        Ok(Value::from(this_fixed_num))
    }

    /// `Number.prototype.toLocaleString( [locales [, options]] )`
    ///
    /// The `toLocaleString()` method returns a string with a language-sensitive representation of this number.
    ///
    /// Note that while this technically conforms to the Ecma standard, it does no actual
    /// internationalization logic.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-number.prototype.tolocalestring
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toLocaleString
    #[allow(clippy::wrong_self_convention)]
    pub(crate) fn to_locale_string(
        this: &Value,
        _: &[Value],
        context: &mut Context,
    ) -> Result<Value> {
        let this_num = Self::this_number_value(this, context)?;
        let this_str_num = format!("{}", this_num);
        Ok(Value::from(this_str_num))
    }

    /// flt_str_to_exp - used in to_precision
    ///
    /// This function traverses a string representing a number,
    /// returning the floored log10 of this number.
    ///
    fn flt_str_to_exp(flt: &str) -> i32 {
        let mut non_zero_encountered = false;
        let mut dot_encountered = false;
        for (i, c) in flt.chars().enumerate() {
            if c == '.' {
                if non_zero_encountered {
                    return (i as i32) - 1;
                }
                dot_encountered = true;
            } else if c != '0' {
                if dot_encountered {
                    return 1 - (i as i32);
                }
                non_zero_encountered = true;
            }
        }
        (flt.len() as i32) - 1
    }

    /// round_to_precision - used in to_precision
    ///
    /// This procedure has two roles:
    /// - If there are enough or more than enough digits in the
    ///   string to show the required precision, the number
    ///   represented by these digits is rounded using string
    ///   manipulation.
    /// - Else, zeroes are appended to the string.
    ///
    /// When this procedure returns, `digits` is exactly `precision` long.
    ///
    fn round_to_precision(digits: &mut String, precision: usize) {
        if digits.len() > precision {
            let to_round = digits.split_off(precision);
            let mut digit = digits.pop().unwrap() as u8;

            for c in to_round.chars() {
                match c {
                    c if c < '4' => break,
                    c if c > '4' => {
                        digit += 1;
                        break;
                    }
                    _ => {}
                }
            }

            digits.push(digit as char);
        } else {
            digits.push_str(&"0".repeat(precision - digits.len()));
        }
    }

    /// `Number.prototype.toPrecision( [precision] )`
    ///
    /// The `toPrecision()` method returns a string representing the Number object to the specified precision.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-number.prototype.toprecision
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toPrecision
    #[allow(clippy::wrong_self_convention)]
    pub(crate) fn to_precision(
        this: &Value,
        args: &[Value],
        context: &mut Context,
    ) -> Result<Value> {
        let precision_var = args.get(0).cloned().unwrap_or_default();

        // 1 & 6
        let mut this_num = Self::this_number_value(this, context)?;
        // 2 & 4
        if precision_var == Value::undefined() || !this_num.is_finite() {
            return Self::to_string(this, &[], context);
        }

        // 3
        let precision = match precision_var.to_integer_or_infinity(context)? {
            IntegerOrInfinity::Integer(x) if (1..=100).contains(&x) => x as usize,
            _ => {
                // 5
                return context.throw_range_error(
                    "precision must be an integer at least 1 and no greater than 100",
                );
            }
        };
        let precision_i32 = precision as i32;

        // 7
        let mut prefix = String::new(); // spec: 's'
        let mut suffix: String; // spec: 'm'
        let exponent: i32; // spec: 'e'

        // 8
        if this_num < 0.0 {
            prefix.push('-');
            this_num = -this_num;
        }

        // 9
        if this_num == 0.0 {
            suffix = "0".repeat(precision);
            exponent = 0;
        // 10
        } else {
            // Due to f64 limitations, this part differs a bit from the spec,
            // but has the same effect. It manipulates the string constructed
            // by ryu-js: digits with an optional dot between two of them.

            let mut buffer = ryu_js::Buffer::new();
            suffix = buffer.format(this_num).to_string();

            // a: getting an exponent
            exponent = Self::flt_str_to_exp(&suffix);
            // b: getting relevant digits only
            if exponent < 0 {
                suffix = suffix.split_off((1 - exponent) as usize);
            } else if let Some(n) = suffix.find('.') {
                suffix.remove(n);
            }
            // impl: having exactly `precision` digits in `suffix`
            Self::round_to_precision(&mut suffix, precision);

            // c: switching to scientific notation
            let great_exp = exponent >= precision_i32;
            if exponent < -6 || great_exp {
                // ii
                if precision > 1 {
                    suffix.insert(1, '.');
                }
                // vi
                suffix.push('e');
                // iii
                if great_exp {
                    suffix.push('+');
                }
                // iv, v
                suffix.push_str(&exponent.to_string());

                return Ok(Value::from(prefix + &suffix));
            }
        }

        // 11
        let e_inc = exponent + 1;
        if e_inc == precision_i32 {
            return Ok(Value::from(prefix + &suffix));
        }

        // 12
        if exponent >= 0 {
            suffix.insert(e_inc as usize, '.');
        // 13
        } else {
            prefix.push('0');
            prefix.push('.');
            prefix.push_str(&"0".repeat(-e_inc as usize));
        }

        // 14
        Ok(Value::from(prefix + &suffix))
    }

    // https://golang.org/src/math/nextafter.go
    #[inline]
    fn next_after(x: f64, y: f64) -> f64 {
        if x.is_nan() || y.is_nan() {
            f64::NAN
        } else if (x - y) == 0. {
            x
        } else if x == 0.0 {
            f64::from_bits(1).copysign(y)
        } else if y > x || x > 0.0 {
            f64::from_bits(x.to_bits() + 1)
        } else {
            f64::from_bits(x.to_bits() - 1)
        }
    }

    // https://chromium.googlesource.com/v8/v8/+/refs/heads/master/src/numbers/conversions.cc#1230
    #[allow(clippy::wrong_self_convention)]
    pub(crate) fn to_native_string_radix(mut value: f64, radix: u8) -> String {
        assert!(radix >= 2);
        assert!(radix <= 36);
        assert!(value.is_finite());
        // assert_ne!(0.0, value);

        // Character array used for conversion.
        // Temporary buffer for the result. We start with the decimal point in the
        // middle and write to the left for the integer part and to the right for the
        // fractional part. 1024 characters for the exponent and 52 for the mantissa
        // either way, with additional space for sign, decimal point and string
        // termination should be sufficient.
        let mut buffer: [u8; BUF_SIZE] = [0; BUF_SIZE];
        let (int_buf, frac_buf) = buffer.split_at_mut(BUF_SIZE / 2);
        let mut fraction_cursor = 0;
        let negative = value.is_sign_negative();
        if negative {
            value = -value
        }
        // Split the value into an integer part and a fractional part.
        // let mut integer = value.trunc();
        // let mut fraction = value.fract();
        let mut integer = value.floor();
        let mut fraction = value - integer;

        // We only compute fractional digits up to the input double's precision.
        let mut delta = 0.5 * (Self::next_after(value, f64::MAX) - value);
        delta = Self::next_after(0.0, f64::MAX).max(delta);
        assert!(delta > 0.0);
        if fraction >= delta {
            // Insert decimal point.
            frac_buf[fraction_cursor] = b'.';
            fraction_cursor += 1;
            loop {
                // Shift up by one digit.
                fraction *= radix as f64;
                delta *= radix as f64;
                // Write digit.
                let digit = fraction as u32;
                frac_buf[fraction_cursor] =
                    std::char::from_digit(digit, radix as u32).unwrap() as u8;
                fraction_cursor += 1;
                // Calculate remainder.
                fraction -= digit as f64;
                // Round to even.
                if fraction + delta > 1.0
                    && (fraction > 0.5 || (fraction - 0.5).abs() < f64::EPSILON && digit & 1 != 0)
                {
                    loop {
                        // We need to back trace already written digits in case of carry-over.
                        fraction_cursor -= 1;
                        if fraction_cursor == 0 {
                            //              CHECK_EQ('.', buffer[fraction_cursor]);
                            // Carry over to the integer part.
                            integer += 1.;
                            break;
                        } else {
                            let c: u8 = frac_buf[fraction_cursor];
                            // Reconstruct digit.
                            let digit_0 = (c as char).to_digit(10).unwrap();
                            if digit_0 + 1 >= radix as u32 {
                                continue;
                            }
                            frac_buf[fraction_cursor] =
                                std::char::from_digit(digit_0 + 1, radix as u32).unwrap() as u8;
                            fraction_cursor += 1;
                            break;
                        }
                    }
                    break;
                }
                if fraction < delta {
                    break;
                }
            }
        }

        // Compute integer digits. Fill unrepresented digits with zero.
        let mut int_iter = int_buf.iter_mut().enumerate().rev(); //.rev();
        while FloatCore::integer_decode(integer / f64::from(radix)).1 > 0 {
            integer /= radix as f64;
            *int_iter.next().unwrap().1 = b'0';
        }

        loop {
            let remainder = integer % (radix as f64);
            *int_iter.next().unwrap().1 =
                std::char::from_digit(remainder as u32, radix as u32).unwrap() as u8;
            integer = (integer - remainder) / radix as f64;
            if integer <= 0f64 {
                break;
            }
        }
        // Add sign and terminate string.
        if negative {
            *int_iter.next().unwrap().1 = b'-';
        }
        assert!(fraction_cursor < BUF_SIZE);

        let integer_cursor = int_iter.next().unwrap().0 + 1;
        let fraction_cursor = fraction_cursor + BUF_SIZE / 2;
        // dbg!("Number: {}, Radix: {}, Cursors: {}, {}", value, radix, integer_cursor, fraction_cursor);
        String::from_utf8_lossy(&buffer[integer_cursor..fraction_cursor]).into()
    }

    #[allow(clippy::wrong_self_convention)]
    pub(crate) fn to_native_string(x: f64) -> String {
        let mut buffer = ryu_js::Buffer::new();
        buffer.format(x).to_string()
    }

    /// `Number.prototype.toString( [radix] )`
    ///
    /// The `toString()` method returns a string representing the specified Number object.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-number.prototype.tostring
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toString
    #[allow(clippy::wrong_self_convention)]
    pub(crate) fn to_string(this: &Value, args: &[Value], context: &mut Context) -> Result<Value> {
        // 1. Let x be ? thisNumberValue(this value).
        let x = Self::this_number_value(this, context)?;

        // 2. If radix is undefined, let radixNumber be 10.
        // 3. Else, let radixNumber be ? ToInteger(radix).
        let radix = args
            .get(0)
            .map(|arg| arg.to_integer(context))
            .transpose()?
            .map_or(10, |radix| radix as u8);

        // 4. If radixNumber < 2 or radixNumber > 36, throw a RangeError exception.
        if !(2..=36).contains(&radix) {
            return context
                .throw_range_error("radix must be an integer at least 2 and no greater than 36");
        }

        // 5. If radixNumber = 10, return ! ToString(x).
        if radix == 10 {
            return Ok(Value::from(Self::to_native_string(x)));
        }

        if x == -0. {
            return Ok(Value::from("0"));
        } else if x.is_nan() {
            return Ok(Value::from("NaN"));
        } else if x.is_infinite() && x.is_sign_positive() {
            return Ok(Value::from("Infinity"));
        } else if x.is_infinite() && x.is_sign_negative() {
            return Ok(Value::from("-Infinity"));
        }

        // This is a Optimization from the v8 source code to print values that can fit in a single character
        // Since the actual num_to_string allocates a 2200 bytes buffer for actual conversion
        // I am not sure if this part is effective as the v8 equivalent https://chromium.googlesource.com/v8/v8/+/refs/heads/master/src/builtins/number.tq#53
        // // Fast case where the result is a one character string.
        // if x.is_sign_positive() && x.fract() == 0.0 && x < radix_number as f64 {
        //     return Ok(to_value(format!("{}", std::char::from_digit(x as u32, radix_number as u32).unwrap())))
        // }

        // 6. Return the String representation of this Number value using the radix specified by radixNumber.
        Ok(Value::from(Self::to_native_string_radix(x, radix)))
    }

    /// `Number.prototype.toString()`
    ///
    /// The `valueOf()` method returns the wrapped primitive value of a Number object.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-number.prototype.valueof
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/valueOf
    pub(crate) fn value_of(this: &Value, _: &[Value], context: &mut Context) -> Result<Value> {
        Ok(Value::from(Self::this_number_value(this, context)?))
    }

    /// Builtin javascript 'parseInt(str, radix)' function.
    ///
    /// Parses the given string as an integer using the given radix as a base.
    ///
    /// An argument of type Number (i.e. Integer or Rational) is also accepted in place of string.
    ///
    /// The radix must be an integer in the range [2, 36] inclusive.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-parseint-string-radix
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt
    pub(crate) fn parse_int(_: &Value, args: &[Value], context: &mut Context) -> Result<Value> {
        if let (Some(val), radix) = (args.get(0), args.get(1)) {
            // 1. Let inputString be ? ToString(string).
            let input_string = val.to_string(context)?;

            // 2. Let S be ! TrimString(inputString, start).
            let mut var_s = input_string.trim();

            // 3. Let sign be 1.
            // 4. If S is not empty and the first code unit of S is the code unit 0x002D (HYPHEN-MINUS),
            //    set sign to -1.
            let sign = if !var_s.is_empty() && var_s.starts_with('\u{002D}') {
                -1
            } else {
                1
            };

            // 5. If S is not empty and the first code unit of S is the code unit 0x002B (PLUS SIGN) or
            //    the code unit 0x002D (HYPHEN-MINUS), remove the first code unit from S.
            if !var_s.is_empty() {
                var_s = var_s
                    .strip_prefix(&['\u{002B}', '\u{002D}'][..])
                    .unwrap_or(var_s);
            }

            // 6. Let R be ℝ(? ToInt32(radix)).
            let mut var_r = radix.cloned().unwrap_or_default().to_i32(context)?;

            // 7. Let stripPrefix be true.
            let mut strip_prefix = true;

            // 8. If R ≠ 0, then
            if var_r != 0 {
                //     a. If R < 2 or R > 36, return NaN.
                if !(2..=36).contains(&var_r) {
                    return Ok(Value::nan());
                }

                //     b. If R ≠ 16, set stripPrefix to false.
                if var_r != 16 {
                    strip_prefix = false
                }
            } else {
                // 9. Else,
                //     a. Set R to 10.
                var_r = 10;
            }

            // 10. If stripPrefix is true, then
            //     a. If the length of S is at least 2 and the first two code units of S are either "0x" or "0X", then
            //         i. Remove the first two code units from S.
            //         ii. Set R to 16.
            if strip_prefix
                && var_s.len() >= 2
                && (var_s.starts_with("0x") || var_s.starts_with("0X"))
            {
                var_s = var_s.split_at(2).1;

                var_r = 16;
            }

            // 11. If S contains a code unit that is not a radix-R digit, let end be the index within S of the
            //     first such code unit; otherwise, let end be the length of S.
            let end = if let Some(index) = var_s.find(|c: char| !c.is_digit(var_r as u32)) {
                index
            } else {
                var_s.len()
            };

            // 12. Let Z be the substring of S from 0 to end.
            let var_z = var_s.split_at(end).0;

            // 13. If Z is empty, return NaN.
            if var_z.is_empty() {
                return Ok(Value::nan());
            }

            // 14. Let mathInt be the integer value that is represented by Z in radix-R notation, using the
            //     letters A-Z and a-z for digits with values 10 through 35. (However, if R is 10 and Z contains
            //     more than 20 significant digits, every significant digit after the 20th may be replaced by a
            //     0 digit, at the option of the implementation; and if R is not 2, 4, 8, 10, 16, or 32, then
            //     mathInt may be an implementation-approximated value representing the integer value that is
            //     represented by Z in radix-R notation.)
            let math_int = u64::from_str_radix(var_z, var_r as u32).map_or_else(
                |_| f64::from_str_radix(var_z, var_r as u32).expect("invalid_float_conversion"),
                |i| i as f64,
            );

            // 15. If mathInt = 0, then
            //     a. If sign = -1, return -0𝔽.
            //     b. Return +0𝔽.
            if math_int == 0_f64 {
                if sign == -1 {
                    return Ok(Value::rational(-0_f64));
                } else {
                    return Ok(Value::rational(0_f64));
                }
            }

            // 16. Return 𝔽(sign × mathInt).
            Ok(Value::rational(f64::from(sign) * math_int))
        } else {
            // Not enough arguments to parseInt.
            Ok(Value::nan())
        }
    }

    /// Builtin javascript 'parseFloat(str)' function.
    ///
    /// Parses the given string as a floating point value.
    ///
    /// An argument of type Number (i.e. Integer or Rational) is also accepted in place of string.
    ///
    /// To improve performance an Integer type Number is returned in place of a Rational if the given
    /// string can be parsed and stored as an Integer.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-parsefloat-string
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseFloat
    pub(crate) fn parse_float(_: &Value, args: &[Value], _ctx: &mut Context) -> Result<Value> {
        if let Some(val) = args.get(0) {
            match val {
                Value::String(s) => {
                    if let Ok(i) = s.parse::<i32>() {
                        // Attempt to parse an integer first so that it can be stored as an integer
                        // to improve performance
                        Ok(Value::integer(i))
                    } else if let Ok(f) = s.parse::<f64>() {
                        Ok(Value::rational(f))
                    } else {
                        // String can't be parsed.
                        Ok(Value::from(f64::NAN))
                    }
                }
                Value::Integer(i) => Ok(Value::integer(*i)),
                Value::Rational(f) => Ok(Value::rational(*f)),
                _ => {
                    // Wrong argument type to parseFloat.
                    Ok(Value::from(f64::NAN))
                }
            }
        } else {
            // Not enough arguments to parseFloat.
            Ok(Value::from(f64::NAN))
        }
    }

    /// Builtin javascript 'isFinite(number)' function.
    ///
    /// Converts the argument to a number, throwing a type error if the conversion is invalid.
    ///
    /// If the number is NaN, +∞, or -∞ false is returned.
    ///
    /// Otherwise true is returned.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-isfinite-number
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isFinite
    pub(crate) fn global_is_finite(
        _: &Value,
        args: &[Value],
        context: &mut Context,
    ) -> Result<Value> {
        if let Some(value) = args.get(0) {
            let number = value.to_number(context)?;
            Ok(number.is_finite().into())
        } else {
            Ok(false.into())
        }
    }

    /// Builtin javascript 'isNaN(number)' function.
    ///
    /// Converts the argument to a number, throwing a type error if the conversion is invalid.
    ///
    /// If the number is NaN true is returned.
    ///
    /// Otherwise false is returned.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-isnan-number
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN
    pub(crate) fn global_is_nan(_: &Value, args: &[Value], context: &mut Context) -> Result<Value> {
        if let Some(value) = args.get(0) {
            let number = value.to_number(context)?;
            Ok(number.is_nan().into())
        } else {
            Ok(true.into())
        }
    }

    /// `Number.isFinite( number )`
    ///
    /// Checks if the argument is a number, returning false if it isn't.
    ///
    /// If the number is NaN, +∞, or -∞ false is returned.
    ///
    /// Otherwise true is returned.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-number.isfinite
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isFinite
    pub(crate) fn number_is_finite(_: &Value, args: &[Value], _ctx: &mut Context) -> Result<Value> {
        Ok(Value::from(if let Some(val) = args.get(0) {
            match val {
                Value::Integer(_) => true,
                Value::Rational(number) => number.is_finite(),
                _ => false,
            }
        } else {
            false
        }))
    }

    /// `Number.isInteger( number )`
    ///
    /// Checks if the argument is an integer.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-number.isinteger
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isInteger
    pub(crate) fn number_is_integer(
        _: &Value,
        args: &[Value],
        _ctx: &mut Context,
    ) -> Result<Value> {
        Ok(args.get(0).map_or(false, Self::is_integer).into())
    }

    /// `Number.isNaN( number )`
    ///
    /// Checks if the argument is a number, returning false if it isn't.
    ///
    /// If the number is NaN true is returned.
    ///
    /// Otherwise false is returned.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-isnan-number
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isNaN
    pub(crate) fn number_is_nan(_: &Value, args: &[Value], _ctx: &mut Context) -> Result<Value> {
        Ok(Value::from(if let Some(val) = args.get(0) {
            match val {
                Value::Integer(_) => false,
                Value::Rational(number) => number.is_nan(),
                _ => false,
            }
        } else {
            false
        }))
    }

    /// `Number.isSafeInteger( number )`
    ///
    /// Checks if the argument is an integer, returning false if it isn't.
    ///
    /// If abs(number) ≤ MAX_SAFE_INTEGER true is returned.
    ///
    /// Otherwise false is returned.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///  - [MDN documentation][mdn]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-isnan-number
    /// [mdn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isNaN
    pub(crate) fn is_safe_integer(_: &Value, args: &[Value], _ctx: &mut Context) -> Result<Value> {
        Ok(Value::from(match args.get(0) {
            Some(Value::Integer(_)) => true,
            Some(Value::Rational(number)) if Self::is_float_integer(*number) => {
                number.abs() <= Number::MAX_SAFE_INTEGER
            }
            _ => false,
        }))
    }

    /// Checks if the argument is a finite integer Number value.
    ///
    /// More information:
    ///  - [ECMAScript reference][spec]
    ///
    /// [spec]: https://tc39.es/ecma262/#sec-isinteger
    #[inline]
    pub(crate) fn is_integer(val: &Value) -> bool {
        match val {
            Value::Integer(_) => true,
            Value::Rational(number) => Number::is_float_integer(*number),
            _ => false,
        }
    }

    /// Checks if the float argument is an integer.
    #[inline]
    #[allow(clippy::float_cmp)]
    pub(crate) fn is_float_integer(number: f64) -> bool {
        number.is_finite() && number.abs().floor() == number.abs()
    }

    /// The abstract operation Number::equal takes arguments
    /// x (a Number) and y (a Number). It performs the following steps when called:
    ///
    /// <https://tc39.es/ecma262/#sec-numeric-types-number-equal>
    #[inline]
    #[allow(clippy::float_cmp)]
    pub(crate) fn equal(x: f64, y: f64) -> bool {
        x == y
    }

    /// The abstract operation Number::sameValue takes arguments
    /// x (a Number) and y (a Number). It performs the following steps when called:
    ///
    /// <https://tc39.es/ecma262/#sec-numeric-types-number-sameValue>
    #[allow(clippy::float_cmp)]
    pub(crate) fn same_value(a: f64, b: f64) -> bool {
        if a.is_nan() && b.is_nan() {
            return true;
        }

        if a == 0.0 && b == 0.0 {
            if (a.is_sign_negative() && b.is_sign_positive())
                || (a.is_sign_positive() && b.is_sign_negative())
            {
                return false;
            };
            true
        } else {
            a == b
        }
    }

    /// The abstract operation Number::sameValueZero takes arguments
    /// x (a Number) and y (a Number). It performs the following steps when called:
    ///
    /// <https://tc39.es/ecma262/#sec-numeric-types-number-sameValueZero>
    #[inline]
    #[allow(clippy::float_cmp)]
    pub(crate) fn same_value_zero(x: f64, y: f64) -> bool {
        if x.is_nan() && y.is_nan() {
            return true;
        }

        x == y
    }

    #[inline]
    #[allow(clippy::float_cmp)]
    pub(crate) fn less_than(x: f64, y: f64) -> AbstractRelation {
        if x.is_nan() || y.is_nan() {
            return AbstractRelation::Undefined;
        }
        if x == y || x == 0.0 && y == -0.0 || x == -0.0 && y == 0.0 {
            return AbstractRelation::False;
        }
        if x.is_infinite() && x.is_sign_positive() {
            return AbstractRelation::False;
        }
        if y.is_infinite() && y.is_sign_positive() {
            return AbstractRelation::True;
        }
        if x.is_infinite() && x.is_sign_negative() {
            return AbstractRelation::True;
        }
        if y.is_infinite() && y.is_sign_negative() {
            return AbstractRelation::False;
        }
        (x < y).into()
    }
}