From 5a9c128a0313df72973259bea946262cb8973d86 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Mo=CC=88hrmann?= <martisch@uos.de>
Date: Fri, 19 Feb 2016 22:45:38 +0100
Subject: [PATCH] fmt: remove math package dependency and avoid float
 operations

Remove floating point comparisons and rely only on the information
directly provided by appendFloat.
Make restoring the zero padding flag explicit instead of using a defer.
Rearrange some case distinctions to remove duplicated code.
Add more test cases for zero padded floating point numbers with sign.

benchmark                   old ns/op     new ns/op     delta
BenchmarkSprintfFloat-4     187           180           -3.74%

Change-Id: Ifa2ae85257909f40b1b18118c92b516933271729
Reviewed-on: https://go-review.googlesource.com/19721
Reviewed-by: Rob Pike <r@golang.org>
---
 src/fmt/fmt_test.go |  6 ++++++
 src/fmt/format.go   | 43 +++++++++++++++++--------------------------
 2 files changed, 23 insertions(+), 26 deletions(-)

diff --git a/src/fmt/fmt_test.go b/src/fmt/fmt_test.go
index 793f709a79..8d7c36ceb1 100644
--- a/src/fmt/fmt_test.go
+++ b/src/fmt/fmt_test.go
@@ -259,6 +259,12 @@ var fmtTests = []struct {
 	{"%+.3F", float32(-1.0), "-1.000"},
 	{"%+07.2f", 1.0, "+001.00"},
 	{"%+07.2f", -1.0, "-001.00"},
+	{"%-07.2f", 1.0, "1.00   "},
+	{"%-07.2f", -1.0, "-1.00  "},
+	{"%+-07.2f", 1.0, "+1.00  "},
+	{"%+-07.2f", -1.0, "-1.00  "},
+	{"%-+07.2f", 1.0, "+1.00  "},
+	{"%-+07.2f", -1.0, "-1.00  "},
 	{"%+10.2f", +1.0, "     +1.00"},
 	{"%+10.2f", -1.0, "     -1.00"},
 	{"% .3E", -1.0, "-1.000E+00"},
diff --git a/src/fmt/format.go b/src/fmt/format.go
index 517b18f7d4..bf9d00bbc0 100644
--- a/src/fmt/format.go
+++ b/src/fmt/format.go
@@ -5,7 +5,6 @@
 package fmt
 
 import (
-	"math"
 	"strconv"
 	"unicode/utf8"
 )
@@ -405,42 +404,34 @@ func doPrec(f *fmt, def int) int {
 // formatFloat formats a float64; it is an efficient equivalent to  f.pad(strconv.FormatFloat()...).
 func (f *fmt) formatFloat(v float64, verb byte, prec, n int) {
 	// Format number, reserving space for leading + sign if needed.
-	num := strconv.AppendFloat(f.intbuf[0:1], v, verb, prec, n)
+	num := strconv.AppendFloat(f.intbuf[:1], v, verb, prec, n)
 	if num[1] == '-' || num[1] == '+' {
 		num = num[1:]
 	} else {
 		num[0] = '+'
 	}
-	// Special handling for infinity, which doesn't look like a number so shouldn't be padded with zeros.
-	if math.IsInf(v, 0) {
-		if f.zero {
-			defer func() { f.zero = true }()
-			f.zero = false
-		}
-	}
-	// num is now a signed version of the number.
-	// If we're zero padding, want the sign before the leading zeros.
-	// Achieve this by writing the sign out and then padding the unsigned number.
-	if f.zero && f.widPresent && f.wid > len(num) {
-		if f.space && v >= 0 {
-			f.buf.WriteByte(' ') // This is what C does: even with zero, f.space means space.
-			f.wid--
-		} else if f.plus || v < 0 {
-			f.buf.WriteByte(num[0])
-			f.wid--
-		}
-		f.pad(num[1:])
-		return
-	}
 	// f.space says to replace a leading + with a space.
 	if f.space && num[0] == '+' {
 		num[0] = ' '
+	}
+	// Special handling for "+Inf" and "-Inf",
+	// which don't look like a number so shouldn't be padded with zeros.
+	if num[1] == 'I' {
+		oldZero := f.zero
+		f.zero = false
 		f.pad(num)
+		f.zero = oldZero
 		return
 	}
-	// Now we know the sign is attached directly to the number, if present at all.
-	// We want a sign if asked for, if it's negative, or if it's infinity (+Inf vs. -Inf).
-	if f.plus || num[0] == '-' || math.IsInf(v, 0) {
+	// We want a sign if asked for and if the sign is not positive.
+	if f.plus || num[0] != '+' {
+		// If we're zero padding we want the sign before the leading zeros.
+		// Achieve this by writing the sign out and then padding the unsigned number.
+		if f.zero && f.widPresent && f.wid > len(num) {
+			f.buf.WriteByte(num[0])
+			f.wid--
+			num = num[1:]
+		}
 		f.pad(num)
 		return
 	}