diff --git a/spec.html b/spec.html index fcf3db959c..319f48a0cb 100644 --- a/spec.html +++ b/spec.html @@ -4458,53 +4458,68 @@

Syntax

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Runtime Semantics: MV

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The conversion of a String to a Number value is similar overall to the determination of the Number value for a numeric literal (see ), but some of the details are different, so the process for converting a String numeric literal to a value of Number type is given here. This value is determined in two steps: first, a mathematical value (MV) is derived from the String numeric literal; second, this mathematical value is rounded as described below. The MV on any grammar symbol, not provided below, is the MV for that symbol defined in .

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Once the exact MV for a String numeric literal has been determined, it is then rounded to a value of the Number type. If the MV is 0, then the rounded value is *+0*𝔽 unless the first non white space code point in the String numeric literal is `-`, in which case the rounded value is *-0*𝔽. Otherwise, the rounded value must be the Number value for the MV (in the sense defined in ), unless the literal includes a |StrUnsignedDecimalLiteral| and the literal has more than 20 significant digits, in which case the Number value may be either the Number value for the MV of a literal produced by replacing each significant digit after the 20th with a 0 digit or the Number value for the MV of a literal produced by replacing each significant digit after the 20th with a 0 digit and then incrementing the literal at the 20th digit position. A digit is significant if it is not part of an |ExponentPart| and

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Runtime Semantics: StringNumericValue

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The conversion of a String to a Number value is similar overall to the determination of the Number value for a numeric literal (see ), but some of the details are different, so the process for converting a String numeric literal to a value of the Number type is given here.

+ StringNumericLiteral ::: StrWhiteSpace? + + 1. Return *+0*𝔽. + + StringNumericLiteral ::: StrWhiteSpace? StrNumericLiteral StrWhiteSpace? + + 1. Return StringNumericValue of |StrNumericLiteral|. + + StrNumericLiteral ::: NonDecimalIntegerLiteral + + 1. Return 𝔽(MV of |NonDecimalIntegerLiteral|). + + StrDecimalLiteral ::: `-` StrUnsignedDecimalLiteral + + 1. Let _a_ be StringNumericValue of |StrUnsignedDecimalLiteral|. + 1. If _a_ is *+0*𝔽, return *-0*𝔽. + 1. Return -_a_. + + StrUnsignedDecimalLiteral ::: `Infinity` + + 1. Return *+∞*𝔽. + + StrUnsignedDecimalLiteral ::: DecimalDigits `.` DecimalDigits? ExponentPart? + + 1. Let _a_ be MV of the first |DecimalDigits|. + 1. If the second |DecimalDigits| is present, then + 1. Let _b_ be MV of the second |DecimalDigits|. + 1. Let _n_ be the number of code points in the second |DecimalDigits|. + 1. Else, + 1. Let _b_ be 0. + 1. Let _n_ be 0. + 1. If |ExponentPart| is present, let _e_ be MV of |ExponentPart|. Otherwise, let _e_ be 0. + 1. Return RoundMVResult((_a_ + (_b_ × 10-_n_)) × 10_e_). + + StrUnsignedDecimalLiteral ::: `.` DecimalDigits ExponentPart? + + 1. Let _b_ be MV of |DecimalDigits|. + 1. If |ExponentPart| is present, let _e_ be MV of |ExponentPart|. Otherwise, let _e_ be 0. + 1. Let _n_ be the number of code points in |DecimalDigits|. + 1. Return RoundMVResult(_b_ × 10_e_ - _n_). + + StrUnsignedDecimalLiteral ::: DecimalDigits ExponentPart? + + 1. Let _a_ be MV of |DecimalDigits|. + 1. If |ExponentPart| is present, let _e_ be MV of |ExponentPart|. Otherwise, let _e_ be 0. + 1. Return RoundMVResult(_a_ × 10_e_). + + + + +

RoundMVResult ( _n_ )

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The abstract operation RoundMVResult takes argument _n_ (a mathematical value). It converts _n_ to a Number in an implementation-defined manner. For the purposes of this abstract operation, a digit is significant if it is not zero or there is a non-zero digit to its left and there is a non-zero digit to its right. For the purposes of this abstract operation, "the mathematical value denoted by" a representation of a mathematical value is the inverse of "the decimal representation of" a mathematical value. It performs the following steps when called:

+ + 1. If the decimal representation of _n_ has 20 or fewer significant digits, return 𝔽(_n_). + 1. Let _option1_ be the mathematical value denoted by the result of replacing each significant digit in the decimal representation of _n_ after the 20th with a 0 digit. + 1. Let _option2_ be the mathematical value denoted by the result of replacing each significant digit in the decimal representation of _n_ after the 20th with a 0 digit and then incrementing it at the 20th position (with carrying as necessary). + 1. Let _chosen_ be an implementation-defined choice of either _option1_ or _option2_. + 1. Return 𝔽(_chosen_). + @@ -14183,22 +14198,12 @@

Static Semantics: MV

Static Semantics: NumericValue

NumericLiteral :: DecimalLiteral - 1. Return the Number value that results from rounding the MV of |DecimalLiteral| as described below. + 1. Return RoundMVResult(MV of |DecimalLiteral|). NumericLiteral :: NonDecimalIntegerLiteral - 1. Return the Number value that results from rounding the MV of |NonDecimalIntegerLiteral| as described below. + 1. Return 𝔽(MV of |NonDecimalIntegerLiteral|). -

Once the exact MV for a numeric literal has been determined, it is then rounded to a value of the Number type. If the MV is 0, then the rounded value is *+0*𝔽; otherwise, the rounded value must be the Number value for the MV (as specified in ), unless the literal is a |DecimalLiteral| and the literal has more than 20 significant digits, in which case the Number value may be either the Number value for the MV of a literal produced by replacing each significant digit after the 20th with a `0` digit or the Number value for the MV of a literal produced by replacing each significant digit after the 20th with a `0` digit and then incrementing the literal at the 20th significant digit position. A digit is significant if it is not part of an |ExponentPart| and

- - NumericLiteral :: NonDecimalIntegerLiteral BigIntLiteralSuffix 1. Return the BigInt value that represents the MV of |NonDecimalIntegerLiteral|. @@ -24689,11 +24694,9 @@

parseFloat ( _string_ )

1. Let _trimmedString_ be ! TrimString(_inputString_, ~start~). 1. If neither _trimmedString_ nor any prefix of _trimmedString_ satisfies the syntax of a |StrDecimalLiteral| (see ), return *NaN*. 1. Let _numberString_ be the longest prefix of _trimmedString_, which might be _trimmedString_ itself, that satisfies the syntax of a |StrDecimalLiteral|. - 1. Let _mathFloat_ be MV of _numberString_. - 1. If _mathFloat_ = 0, then - 1. If the first code unit of _trimmedString_ is the code unit 0x002D (HYPHEN-MINUS), return *-0*𝔽. - 1. Return *+0*𝔽. - 1. Return 𝔽(_mathFloat_). + 1. Let _parsedNumber_ be ParseText(! StringToCodePoints(_numberString_), |StrDecimalLiteral|). + 1. Assert: _parsedNumber_ is a Parse Node. + 1. Return StringNumericValue of _parsedNumber_.

`parseFloat` may interpret only a leading portion of _string_ as a Number value; it ignores any code units that cannot be interpreted as part of the notation of a decimal literal, and no indication is given that any such code units were ignored.