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// Copyright 2021 Bret Jordan & Benedikt Thoma, All rights reserved.
// Copyright 2006-2019 WebPKI.org (http://webpki.org).
//
// Use of this source code is governed by an Apache 2.0 license that can be
// found in the LICENSE file in the root of the source tree.
package jcs
import (
"errors"
"math"
"strconv"
"strings"
)
const invalidPattern uint64 = 0x7ff0000000000000
// NumberToJSON converts numbers in IEEE-754 double precision into the
// format specified for JSON in EcmaScript Version 6 and forward.
// The core application for this is canonicalization per RFC 8785:
func NumberToJSON(ieeeF64 float64) (res string, err error) {
ieeeU64 := math.Float64bits(ieeeF64)
// Special case: NaN and Infinity are invalid in JSON
if (ieeeU64 & invalidPattern) == invalidPattern {
return "null", errors.New("Invalid JSON number: " + strconv.FormatUint(ieeeU64, 16))
}
// Special case: eliminate "-0" as mandated by the ES6-JSON/JCS specifications
if ieeeF64 == 0 { // Right, this line takes both -0 and 0
return "0", nil
}
// Deal with the sign separately
var sign string = ""
if ieeeF64 < 0 {
ieeeF64 = -ieeeF64
sign = "-"
}
// ES6 has a unique "g" format
var format byte = 'e'
if ieeeF64 < 1e+21 && ieeeF64 >= 1e-6 {
format = 'f'
}
// The following should (in "theory") do the trick:
es6Formatted := strconv.FormatFloat(ieeeF64, format, -1, 64)
// Ryu version
exponent := strings.IndexByte(es6Formatted, 'e')
if exponent > 0 {
// Go outputs "1e+09" which must be rewritten as "1e+9"
if es6Formatted[exponent+2] == '0' {
es6Formatted = es6Formatted[:exponent+2] + es6Formatted[exponent+3:]
}
}
return sign + es6Formatted, nil
}
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