all: add internal/itoa package

This replaces five implementations scattered across low level packages.
(And I plan to use it in a sixth soon.)
Three of the five were byte-for-byte identical.

Change-Id: I3bbbeeac63723a487986c912b604e10ad1e042f4
Reviewed-on: https://go-review.googlesource.com/c/go/+/301549
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>

4 files changed, 75 insertions, 29 deletions

diff --git a/src/internal/itoa/itoa.go b/src/internal/itoa/itoa.go
new file mode 100644
index 0000000000..c6062d9fe1
--- /dev/null
+++ b/src/internal/itoa/itoa.go
@@ -0,0 +1,33 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Simple conversions to avoid depending on strconv.
+
+package itoa
+
+// Itoa converts val to a decimal string.
+func Itoa(val int) string {
+	if val < 0 {
+		return "-" + Uitoa(uint(-val))
+	}
+	return Uitoa(uint(val))
+}
+
+// Uitoa converts val to a decimal string.
+func Uitoa(val uint) string {
+	if val == 0 { // avoid string allocation
+		return "0"
+	}
+	var buf [20]byte // big enough for 64bit value base 10
+	i := len(buf) - 1
+	for val >= 10 {
+		q := val / 10
+		buf[i] = byte('0' + val - q*10)
+		i--
+		val = q
+	}
+	// val < 10
+	buf[i] = byte('0' + val)
+	return string(buf[i:])
+}
diff --git a/src/internal/itoa/itoa_test.go b/src/internal/itoa/itoa_test.go
new file mode 100644
index 0000000000..71931c1e3a
--- /dev/null
+++ b/src/internal/itoa/itoa_test.go
@@ -0,0 +1,40 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package itoa_test
+
+import (
+	"fmt"
+	"internal/itoa"
+	"math"
+	"testing"
+)
+
+var (
+	minInt64  int64  = math.MinInt64
+	maxInt64  int64  = math.MaxInt64
+	maxUint64 uint64 = math.MaxUint64
+)
+
+func TestItoa(t *testing.T) {
+	tests := []int{int(minInt64), math.MinInt32, -999, -100, -1, 0, 1, 100, 999, math.MaxInt32, int(maxInt64)}
+	for _, tt := range tests {
+		got := itoa.Itoa(tt)
+		want := fmt.Sprint(tt)
+		if want != got {
+			t.Fatalf("Itoa(%d) = %s, want %s", tt, got, want)
+		}
+	}
+}
+
+func TestUitoa(t *testing.T) {
+	tests := []uint{0, 1, 100, 999, math.MaxUint32, uint(maxUint64)}
+	for _, tt := range tests {
+		got := itoa.Uitoa(tt)
+		want := fmt.Sprint(tt)
+		if want != got {
+			t.Fatalf("Uitoa(%d) = %s, want %s", tt, got, want)
+		}
+	}
+}
diff --git a/src/internal/poll/fd_io_plan9.go b/src/internal/poll/fd_io_plan9.go
index 287d11bd8c..3205ac8513 100644
--- a/src/internal/poll/fd_io_plan9.go
+++ b/src/internal/poll/fd_io_plan9.go
@@ -5,6 +5,7 @@
 package poll
 
 import (
+	"internal/itoa"
 	"runtime"
 	"sync"
 	"syscall"
@@ -71,7 +72,7 @@ func (aio *asyncIO) Cancel() {
 	if aio.pid == -1 {
 		return
 	}
-	f, e := syscall.Open("/proc/"+itoa(aio.pid)+"/note", syscall.O_WRONLY)
+	f, e := syscall.Open("/proc/"+itoa.Itoa(aio.pid)+"/note", syscall.O_WRONLY)
 	if e != nil {
 		return
 	}
diff --git a/src/internal/poll/strconv.go b/src/internal/poll/strconv.go
index fd5e20f1f4..c98332d3da 100644
--- a/src/internal/poll/strconv.go
+++ b/src/internal/poll/strconv.go
@@ -5,36 +5,8 @@
 //go:build plan9
 // +build plan9
 
-// Simple conversions to avoid depending on strconv.
-
 package poll
 
-// Convert integer to decimal string
-func itoa(val int) string {
-	if val < 0 {
-		return "-" + uitoa(uint(-val))
-	}
-	return uitoa(uint(val))
-}
-
-// Convert unsigned integer to decimal string
-func uitoa(val uint) string {
-	if val == 0 { // avoid string allocation
-		return "0"
-	}
-	var buf [20]byte // big enough for 64bit value base 10
-	i := len(buf) - 1
-	for val >= 10 {
-		q := val / 10
-		buf[i] = byte('0' + val - q*10)
-		i--
-		val = q
-	}
-	// val < 10
-	buf[i] = byte('0' + val)
-	return string(buf[i:])
-}
-
 // stringsHasSuffix is strings.HasSuffix. It reports whether s ends in
 // suffix.
 func stringsHasSuffix(s, suffix string) bool {