diff --git a/source/durandal/crc.rs b/source/durandal/cksum.rs
similarity index 53%
rename from source/durandal/crc.rs
rename to source/durandal/cksum.rs
index 97ec35d..7441ae7 100644
--- a/source/durandal/crc.rs
+++ b/source/durandal/cksum.rs
@@ -3,7 +3,7 @@
 fn crc_accum(a: u32, _: u32) -> u32
 {
    if a & 1 == 1 {
-      0xEDB8_8320 ^ a >> 1
+      ISO_3309_POLYNOMIAL ^ a >> 1
    } else {
       a >> 1
    }
@@ -18,13 +18,36 @@ fn crc_init() -> [u32; 256]
    t
 }
 
+/// Creates an ADLER32 of all bytes in `b`.
+///
+/// # Examples
+///
+/// ```
+/// use maraiah::durandal::cksum::adler32;
+///
+/// assert_eq!(adler32(b"Lorem ipsum dolor sit amet"), 0x83D5_09C5);
+/// ```
+pub fn adler32(b: &[u8]) -> u32
+{
+   let mut x = 1;
+   let mut y = 0;
+
+   for &z in b {
+      let z = u32::from(z);
+      x = (x + z) % ADLER32_MODULO;
+      y = (y + x) % ADLER32_MODULO;
+   }
+
+   (y << 16) | x
+}
+
 /// Creates a CRC-32 of all bytes in `b` with the starting sum `s`. The
 /// polynomial used is the one from ISO-3309.
 ///
 /// # Examples
 ///
 /// ```
-/// use maraiah::durandal::crc::crc32;
+/// use maraiah::durandal::cksum::crc32;
 ///
 /// assert_eq!(crc32(b"Lorem ipsum dolor sit amet", !0), 0x5F29_D461);
 /// ```
@@ -34,4 +57,7 @@ pub fn crc32(b: &[u8], s: u32) -> u32
    !b.iter().fold(s, |a, &o| a >> 8 ^ t[usize::from(a as u8 ^ o)])
 }
 
+const ISO_3309_POLYNOMIAL: u32 = 0xEDB8_8320;
+const ADLER32_MODULO:      u32 = 65521;
+
 // EOF
diff --git a/source/durandal/mod.rs b/source/durandal/mod.rs
index 697ebff..8a3b530 100644
--- a/source/durandal/mod.rs
+++ b/source/durandal/mod.rs
@@ -8,7 +8,7 @@ pub mod cenum;
 pub mod bin;
 
 pub mod bit;
-pub mod crc;
+pub mod cksum;
 pub mod file;
 pub mod fixed;
 pub mod image;