diff --git a/camel.go b/camel.go
index cd5a260..e433f87 100644
--- a/camel.go
+++ b/camel.go
@@ -43,8 +43,8 @@ func toCamelInitCase(s string, initCase bool) string {
 	n.Grow(len(s))
 	capNext := initCase
 	for i, v := range []byte(s) {
-		vIsCap := v >= 'A' && v <= 'Z'
-		vIsLow := v >= 'a' && v <= 'z'
+		vIsCap := capitalLetters.Contains(v)
+		vIsLow := smallLetters.Contains(v)
 		if capNext {
 			if vIsLow {
 				v += 'A'
@@ -59,11 +59,11 @@ func toCamelInitCase(s string, initCase bool) string {
 		if vIsCap || vIsLow {
 			n.WriteByte(v)
 			capNext = false
-		} else if vIsNum := v >= '0' && v <= '9'; vIsNum {
+		} else if vIsNum := numbers.Contains(v); vIsNum {
 			n.WriteByte(v)
 			capNext = true
 		} else {
-			capNext = v == '_' || v == ' ' || v == '-' || v == '.'
+			capNext = separators.Contains(v)
 		}
 	}
 	return n.String()
diff --git a/chars.go b/chars.go
new file mode 100644
index 0000000..a4b5214
--- /dev/null
+++ b/chars.go
@@ -0,0 +1,33 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2015 Ian Coleman
+ * Copyright (c) 2018 Ma_124, <github.com/Ma124>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, Subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or Substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package strcase
+
+import asciiset "github.com/elliotwutingfeng/asciiset"
+
+var numbers, _ = asciiset.MakeASCIISet("0123456789")
+var smallLetters, _ = asciiset.MakeASCIISet("abcdefghijklmnopqrstuvwxyz")
+var capitalLetters, _ = asciiset.MakeASCIISet("ABCDEFGHIJKLMNOPQRSTUVWXYZ")
+var separators, _ = asciiset.MakeASCIISet(" _-.")
diff --git a/go.mod b/go.mod
index a6b5cb6..ae26dd3 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,5 @@
 module github.com/iancoleman/strcase
 
 go 1.16
+
+require github.com/elliotwutingfeng/asciiset v0.0.0-20230602005253-7f88bc28b13f
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..d1d39ee
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,2 @@
+github.com/elliotwutingfeng/asciiset v0.0.0-20230602005253-7f88bc28b13f h1:2zrq6AHwG5HdTmNunOU3tRNPQ0F+R9W8mIxgSJzGwkE=
+github.com/elliotwutingfeng/asciiset v0.0.0-20230602005253-7f88bc28b13f/go.mod h1:GLo/8fDswSAniFG+BFIaiSPcK610jyzgEhWYPQwuQdw=
diff --git a/snake.go b/snake.go
index df018bc..1b2582b 100644
--- a/snake.go
+++ b/snake.go
@@ -68,8 +68,8 @@ func ToScreamingDelimited(s string, delimiter uint8, ignore string, screaming bo
 	n := strings.Builder{}
 	n.Grow(len(s) + 2) // nominal 2 bytes of extra space for inserted delimiters
 	for i, v := range []byte(s) {
-		vIsCap := v >= 'A' && v <= 'Z'
-		vIsLow := v >= 'a' && v <= 'z'
+		vIsCap := capitalLetters.Contains(v)
+		vIsLow := smallLetters.Contains(v)
 		if vIsLow && screaming {
 			v += 'A'
 			v -= 'a'
@@ -81,16 +81,16 @@ func ToScreamingDelimited(s string, delimiter uint8, ignore string, screaming bo
 		// treat acronyms as words, eg for JSONData -> JSON is a whole word
 		if i+1 < len(s) {
 			next := s[i+1]
-			vIsNum := v >= '0' && v <= '9'
-			nextIsCap := next >= 'A' && next <= 'Z'
-			nextIsLow := next >= 'a' && next <= 'z'
-			nextIsNum := next >= '0' && next <= '9'
+			vIsNum := numbers.Contains(v)
+			nextIsCap := capitalLetters.Contains(next)
+			nextIsLow := smallLetters.Contains(next)
+			nextIsNum := numbers.Contains(next)
 			// add underscore if next letter case type is changed
 			if (vIsCap && (nextIsLow || nextIsNum)) || (vIsLow && (nextIsCap || nextIsNum)) || (vIsNum && (nextIsCap || nextIsLow)) {
-				prevIgnore := ignore != "" && i > 0 && strings.ContainsAny(string(s[i-1]), ignore)
+				prevIgnore := ignore != "" && i > 0 && strings.IndexByte(ignore, s[i-1]) != -1
 				if !prevIgnore {
 					if vIsCap && nextIsLow {
-						if prevIsCap := i > 0 && s[i-1] >= 'A' && s[i-1] <= 'Z'; prevIsCap {
+						if prevIsCap := i > 0 && capitalLetters.Contains(s[i-1]); prevIsCap {
 							n.WriteByte(delimiter)
 						}
 					}
@@ -103,7 +103,7 @@ func ToScreamingDelimited(s string, delimiter uint8, ignore string, screaming bo
 			}
 		}
 
-		if (v == ' ' || v == '_' || v == '-' || v == '.') && !strings.ContainsAny(string(v), ignore) {
+		if separators.Contains(v) && strings.IndexByte(ignore, v) == -1 {
 			// replace space/underscore/hyphen/dot with delimiter
 			n.WriteByte(delimiter)
 		} else {