From 5420a8b6744d3b0345ab293f6fcba19c978f1183 Mon Sep 17 00:00:00 2001
From: Prashant Varanasi <github@prashantv.com>
Date: Wed, 28 Mar 2018 12:50:20 -0700
Subject: [PATCH] Use underlying float precision when formatting floats (#353)

Currently, all float values are formatted using 64-bit, but that
incorrectly formats float32 values like 0.01 and 0.99.

See https://play.golang.org/p/jbseI1ivyMW for more context.

Fixes #352.
---
 encode.go      | 8 +++++++-
 encode_test.go | 3 +++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/encode.go b/encode.go
index b3c62b39..a14435e8 100644
--- a/encode.go
+++ b/encode.go
@@ -333,7 +333,13 @@ func (e *encoder) timev(tag string, in reflect.Value) {
 }
 
 func (e *encoder) floatv(tag string, in reflect.Value) {
-	s := strconv.FormatFloat(in.Float(), 'g', -1, 64)
+	// Issue #352: When formatting, use the precision of the underlying value
+	precision := 64
+	if in.Kind() == reflect.Float32 {
+		precision = 32
+	}
+
+	s := strconv.FormatFloat(in.Float(), 'g', -1, precision)
 	switch s {
 	case "+Inf":
 		s = ".inf"
diff --git a/encode_test.go b/encode_test.go
index 0324a909..f0911a76 100644
--- a/encode_test.go
+++ b/encode_test.go
@@ -75,6 +75,9 @@ var marshalTests = []struct {
 	}, {
 		map[string]interface{}{"v": float64(0.1)},
 		"v: 0.1\n",
+	}, {
+		map[string]interface{}{"v": float32(0.99)},
+		"v: 0.99\n",
 	}, {
 		map[string]interface{}{"v": -0.1},
 		"v: -0.1\n",