in internal/encoding/json/encode.go [573:605]
func (bits floatEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
f := v.Float()
if math.IsInf(f, 0) || math.IsNaN(f) {
e.error(&UnsupportedValueError{v, strconv.FormatFloat(f, 'g', -1, int(bits))})
}
// Convert as if by ES6 number to string conversion.
// This matches most other JSON generators.
// See golang.org/issue/6384 and golang.org/issue/14135.
// Like fmt %g, but the exponent cutoffs are different
// and exponents themselves are not padded to two digits.
b := e.AvailableBuffer()
b = mayAppendQuote(b, opts.quoted)
abs := math.Abs(f)
fmt := byte('f')
// Note: Must use float32 comparisons for underlying float32 value to get precise cutoffs right.
if abs != 0 {
if bits == 64 && (abs < 1e-6 || abs >= 1e21) || bits == 32 && (float32(abs) < 1e-6 || float32(abs) >= 1e21) {
fmt = 'e'
}
}
b = strconv.AppendFloat(b, f, fmt, -1, int(bits))
if fmt == 'e' {
// clean up e-09 to e-9
n := len(b)
if n >= 4 && b[n-4] == 'e' && b[n-3] == '-' && b[n-2] == '0' {
b[n-2] = b[n-1]
b = b[:n-1]
}
}
b = mayAppendQuote(b, opts.quoted)
e.Write(b)
}