1// Copyright 2021 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package ascii
6
7import (
8	"strings"
9	"unicode"
10)
11
12// EqualFold is [strings.EqualFold], ASCII only. It reports whether s and t
13// are equal, ASCII-case-insensitively.
14func EqualFold(s, t string) bool {
15	if len(s) != len(t) {
16		return false
17	}
18	for i := 0; i < len(s); i++ {
19		if lower(s[i]) != lower(t[i]) {
20			return false
21		}
22	}
23	return true
24}
25
26// lower returns the ASCII lowercase version of b.
27func lower(b byte) byte {
28	if 'A' <= b && b <= 'Z' {
29		return b + ('a' - 'A')
30	}
31	return b
32}
33
34// IsPrint returns whether s is ASCII and printable according to
35// https://tools.ietf.org/html/rfc20#section-4.2.
36func IsPrint(s string) bool {
37	for i := 0; i < len(s); i++ {
38		if s[i] < ' ' || s[i] > '~' {
39			return false
40		}
41	}
42	return true
43}
44
45// Is returns whether s is ASCII.
46func Is(s string) bool {
47	for i := 0; i < len(s); i++ {
48		if s[i] > unicode.MaxASCII {
49			return false
50		}
51	}
52	return true
53}
54
55// ToLower returns the lowercase version of s if s is ASCII and printable.
56func ToLower(s string) (lower string, ok bool) {
57	if !IsPrint(s) {
58		return "", false
59	}
60	return strings.ToLower(s), true
61}
62