diff --git a/CHANGELOG.md b/CHANGELOG.md
index 54b4c3d..b01a32f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,9 +4,19 @@
 
 * [#26] - Add `memchr` 
 * [#27] - Add `qsort`
+* [#28] - Add `strcat` and `strchr`
+* [#29] - Clean up docs
+* [#30] - Add padding in `sprintf`
+* [#32] - Add `rand`, `srand` and `rand_r`
+* [#34] - Add `strspn` and `strcspn`
 
 [#26]: https://github.com/rust-embedded-community/tinyrlibc/pull/26
 [#27]: https://github.com/rust-embedded-community/tinyrlibc/pull/27
+[#28]: https://github.com/rust-embedded-community/tinyrlibc/pull/28
+[#29]: https://github.com/rust-embedded-community/tinyrlibc/pull/29
+[#30]: https://github.com/rust-embedded-community/tinyrlibc/pull/30
+[#32]: https://github.com/rust-embedded-community/tinyrlibc/pull/32
+[#34]: https://github.com/rust-embedded-community/tinyrlibc/pull/34
 
 ## v0.4.0 (2024-03-22)
 
diff --git a/Cargo.toml b/Cargo.toml
index 62f6d78..d9e6692 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -41,6 +41,8 @@ all = [
     "strncmp",
     "strncpy",
     "strrchr",
+    "strspn",
+    "strcspn",
     "strstr",
     "strtoimax",
     "strtol",
@@ -76,6 +78,8 @@ strncasecmp = []
 strncmp = []
 strncpy = []
 strrchr = []
+strspn = []
+strcspn = []
 strstr = []
 strtoimax = []
 strtol = []
diff --git a/src/lib.rs b/src/lib.rs
index 6b7924e..fd656ef 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -11,58 +11,85 @@
 #![allow(clippy::missing_safety_doc)]
 #![allow(unused_imports)]
 
+// Useful imports
+mod ctype;
+pub use self::ctype::*;
+
+// Stateless implementations.
+// rustfmt will keep these in alphabetical order.
+mod abs;
+mod itoa;
+mod memchr;
+mod qsort;
+mod rand_r;
+mod snprintf;
+mod strcat;
+mod strchr;
+mod strcmp;
+mod strcpy;
+mod strcspn;
+mod strlen;
+mod strncasecmp;
+mod strncmp;
+mod strncpy;
+mod strrchr;
+mod strspn;
+mod strstr;
+mod strtol;
+
+// Stateful implementations (which hence are optional).
+// rustfmt will keep these in alphabetical order.
 #[cfg(feature = "alloc")]
 mod malloc;
-#[cfg(feature = "alloc")]
-pub use self::malloc::{calloc, free, malloc, realloc};
+#[cfg(feature = "rand")]
+mod rand;
+#[cfg(feature = "signal")]
+mod signal;
 
-mod itoa;
+// Public re-exports.
+// rustfmt will keep these in alphabetical order.
+#[cfg(feature = "abs")]
+pub use self::abs::abs;
 #[cfg(feature = "itoa")]
 pub use self::itoa::itoa;
 #[cfg(feature = "utoa")]
 pub use self::itoa::utoa;
-
-mod abs;
-#[cfg(feature = "abs")]
-pub use self::abs::abs;
-
-mod rand_r;
-#[cfg(feature = "rand_r")]
-pub use self::rand_r::{rand_r, RAND_MAX};
-#[cfg(feature = "rand")]
-mod rand;
+#[cfg(feature = "alloc")]
+pub use self::malloc::{calloc, free, malloc, realloc};
+#[cfg(feature = "memchr")]
+pub use self::memchr::memchr;
+#[cfg(feature = "qsort")]
+pub use self::qsort::qsort;
 #[cfg(feature = "rand")]
 pub use self::rand::{rand, srand};
-
-mod strcmp;
+#[cfg(feature = "rand_r")]
+pub use self::rand_r::{rand_r, RAND_MAX};
+#[cfg(feature = "signal")]
+pub use self::signal::{abort, raise, signal};
+#[cfg(feature = "strcat")]
+pub use self::strcat::strcat;
+#[cfg(feature = "strchr")]
+pub use self::strchr::strchr;
 #[cfg(feature = "strcmp")]
 pub use self::strcmp::strcmp;
-
-mod strncmp;
-#[cfg(feature = "strncmp")]
-pub use self::strncmp::strncmp;
-
-mod strncasecmp;
-#[cfg(feature = "strncasecmp")]
-pub use self::strncasecmp::strncasecmp;
-
-mod strcpy;
 #[cfg(feature = "strcpy")]
 pub use self::strcpy::strcpy;
-
-mod strncpy;
-#[cfg(feature = "strncpy")]
-pub use self::strncpy::strncpy;
-
-mod strlen;
+#[cfg(feature = "strcspn")]
+pub use self::strcspn::strcspn;
 #[cfg(feature = "strlen")]
 pub use self::strlen::strlen;
-
-mod strcat;
-#[cfg(feature = "strcat")]
-pub use self::strcat::strcat;
-
-mod strtol;
+#[cfg(feature = "strncasecmp")]
+pub use self::strncasecmp::strncasecmp;
+#[cfg(feature = "strncmp")]
+pub use self::strncmp::strncmp;
+#[cfg(feature = "strncpy")]
+pub use self::strncpy::strncpy;
+#[cfg(feature = "strrchr")]
+pub use self::strrchr::strrchr;
+#[cfg(feature = "strspn")]
+pub use self::strspn::strspn;
+#[cfg(feature = "strstr")]
+pub use self::strstr::strstr;
 #[cfg(feature = "atoi")]
 pub use self::strtol::atoi;
 #[cfg(feature = "isalpha")]
@@ -85,33 +112,3 @@ pub use self::strtol::strtoul;
 pub use self::strtol::strtoull;
 #[cfg(feature = "strtoumax")]
 pub use self::strtol::strtoumax;
-
-mod strstr;
-#[cfg(feature = "strstr")]
-pub use self::strstr::strstr;
-
-mod strchr;
-#[cfg(feature = "strchr")]
-pub use self::strchr::strchr;
-
-mod strrchr;
-#[cfg(feature = "strrchr")]
-pub use self::strrchr::strrchr;
-
-mod qsort;
-#[cfg(feature = "qsort")]
-pub use self::qsort::qsort;
-
-#[cfg(feature = "signal")]
-mod signal;
-#[cfg(feature = "signal")]
-pub use self::signal::{abort, raise, signal};
-
-mod memchr;
-#[cfg(feature = "memchr")]
-pub use self::memchr::memchr;
-
-mod snprintf;
-
-mod ctype;
-pub use self::ctype::*;
diff --git a/src/strcspn.rs b/src/strcspn.rs
new file mode 100644
index 0000000..39a0cc6
--- /dev/null
+++ b/src/strcspn.rs
@@ -0,0 +1,94 @@
+//! Rust implementation of C library function `strcspn`
+//!
+//! Copyright (c) Ferrous Systems UK Ltd
+//! Licensed under the Blue Oak Model Licence 1.0.0
+
+use crate::{CChar, CInt};
+
+/// Rust implementation of C library function `strcspn`
+#[cfg_attr(feature = "strcspn", no_mangle)]
+pub unsafe extern "C" fn strcspn(s: *const CChar, charset: *const CChar) -> usize {
+	if s.is_null() {
+		return 0;
+	}
+	if charset.is_null() {
+		return 0;
+	}
+
+	let s = unsafe { core::ffi::CStr::from_ptr(s.cast()) };
+
+	let charset = unsafe { core::ffi::CStr::from_ptr(charset.cast()) };
+
+	let bytes = s.to_bytes();
+	for (idx, b) in bytes.iter().enumerate() {
+		if is_c_in_charset(*b, charset) {
+			return idx;
+		}
+	}
+
+	bytes.len()
+}
+
+fn is_c_in_charset(c: u8, charset: &core::ffi::CStr) -> bool {
+	for b in charset.to_bytes() {
+		if c == *b {
+			return true;
+		}
+	}
+	false
+}
+
+#[cfg(test)]
+mod test {
+	#[test]
+	fn complete() {
+		let charset = c"0123456789";
+		let s = c"abcdef";
+		assert_eq!(
+			unsafe { super::strcspn(s.as_ptr().cast(), charset.as_ptr().cast()) },
+			6
+		);
+	}
+
+	#[test]
+	fn subset() {
+		let charset = c"0123456789";
+		let s = c"xyz1";
+		assert_eq!(
+			unsafe { super::strcspn(s.as_ptr().cast(), charset.as_ptr().cast()) },
+			3
+		);
+	}
+
+	#[test]
+	fn none() {
+		let charset = c"0123456789";
+		let s = c"567";
+		assert_eq!(
+			unsafe { super::strcspn(s.as_ptr().cast(), charset.as_ptr().cast()) },
+			0
+		);
+	}
+
+	#[test]
+	fn empty_charset() {
+		let charset = c"";
+		let s = c"AABBCCDD";
+		assert_eq!(
+			unsafe { super::strcspn(s.as_ptr().cast(), charset.as_ptr().cast()) },
+			8
+		);
+	}
+
+	#[test]
+	fn empty_string() {
+		let charset = c"0123456789";
+		let s = c"";
+		assert_eq!(
+			unsafe { super::strcspn(s.as_ptr().cast(), charset.as_ptr().cast()) },
+			0
+		);
+	}
+}
+
+// End of file
diff --git a/src/strspn.rs b/src/strspn.rs
new file mode 100644
index 0000000..3a634ed
--- /dev/null
+++ b/src/strspn.rs
@@ -0,0 +1,84 @@
+//! Rust implementation of C library function `strspn`
+//!
+//! Copyright (c) Ferrous Systems UK Ltd
+//! Licensed under the Blue Oak Model Licence 1.0.0
+
+use crate::{CChar, CInt};
+
+/// Rust implementation of C library function `strspn`
+#[cfg_attr(feature = "strspn", no_mangle)]
+pub unsafe extern "C" fn strspn(s: *const CChar, charset: *const CChar) -> usize {
+	if s.is_null() {
+		return 0;
+	}
+	if charset.is_null() {
+		return 0;
+	}
+
+	let s = unsafe { core::ffi::CStr::from_ptr(s.cast()) };
+
+	let charset = unsafe { core::ffi::CStr::from_ptr(charset.cast()) };
+
+	let bytes = s.to_bytes();
+	for (idx, b) in bytes.iter().enumerate() {
+		if !is_c_in_charset(*b, charset) {
+			return idx;
+		}
+	}
+
+	bytes.len()
+}
+
+fn is_c_in_charset(c: u8, charset: &core::ffi::CStr) -> bool {
+	for b in charset.to_bytes() {
+		if c == *b {
+			return true;
+		}
+	}
+	false
+}
+
+#[cfg(test)]
+mod test {
+	#[test]
+	fn complete() {
+		let charset = c"0123456789";
+		let s = c"987654321";
+		assert_eq!(
+			unsafe { super::strspn(s.as_ptr().cast(), charset.as_ptr().cast()) },
+			9
+		);
+	}
+
+	#[test]
+	fn subset() {
+		let charset = c"0123456789";
+		let s = c"98xx7654321";
+		assert_eq!(
+			unsafe { super::strspn(s.as_ptr().cast(), charset.as_ptr().cast()) },
+			2
+		);
+	}
+
+	#[test]
+	fn empty_charset() {
+		let charset = c"";
+		let s = c"AABBCCDD";
+		assert_eq!(
+			unsafe { super::strspn(s.as_ptr().cast(), charset.as_ptr().cast()) },
+			0
+		);
+	}
+
+	#[test]
+	fn empty_string() {
+		let charset = c"0123456789";
+		let s = c"";
+		assert_eq!(
+			unsafe { super::strspn(s.as_ptr().cast(), charset.as_ptr().cast()) },
+			0
+		);
+	}
+}
+
+// End of file