1 files changed, 25 insertions, 1 deletions
diff --git a/src/encoding/json/encode.go b/src/encoding/json/encode.go
index aab912601a..6e43a9d48b 100644
--- a/src/encoding/json/encode.go
+++ b/src/encoding/json/encode.go
@@ -526,7 +526,31 @@ func (bits floatEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
 	if math.IsInf(f, 0) || math.IsNaN(f) {
 		e.error(&UnsupportedValueError{v, strconv.FormatFloat(f, 'g', -1, int(bits))})
 	}
-	b := strconv.AppendFloat(e.scratch[:0], 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.scratch[:0]
+	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]
+		}
+	}
+
 	if opts.quoted {
 		e.WriteByte('"')
 	}