diff --git a/Cargo.toml b/Cargo.toml
index d9d6c1d..fde20ef 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,12 +10,11 @@ documentation = "http://mrhooray.github.io/crc-rs/crc/index.html"
 license = "MIT"
 
 [dependencies]
-
-[dependencies.build_const]
-version = "0.2"
-default-features = false
+util = { path = "./src/util" }
+build_const = { version = "0.2", default-features = false }
 
 [build-dependencies]
+util = { path = "./src/util" }
 build_const = "0.2"
 
 [features]
diff --git a/build.rs b/build.rs
index 45c1627..a4a1d12 100644
--- a/build.rs
+++ b/build.rs
@@ -1,38 +1,6 @@
-
+extern crate util;
 extern crate build_const;
 
-pub fn make_table_crc32(poly: u32) -> [u32; 256] {
-    let mut table = [0u32; 256];
-    for i in 0..256 {
-        let mut value = i as u32;
-        for _ in 0..8 {
-            value = if (value & 1) == 1 {
-                (value >> 1) ^ poly
-            } else {
-                value >> 1
-            }
-        }
-        table[i] = value;
-    }
-    table
-}
-
-pub fn make_table_crc64(poly: u64) -> [u64; 256] {
-    let mut table = [0u64; 256];
-    for i in 0..256 {
-        let mut value = i as u64;
-        for _ in 0..8 {
-            value = if (value & 1) == 1 {
-                (value >> 1) ^ poly
-            } else {
-                value >> 1
-            }
-        }
-        table[i] = value;
-    }
-    table
-}
-
 #[allow(non_snake_case)]
 fn create_constants() {
     let mut crc32 = build_const::ConstWriter::for_build("crc32_constants")
@@ -40,15 +8,15 @@ fn create_constants() {
         .finish_dependencies();
     let CASTAGNOLI: u32 = 0x82f63b78;
     crc32.add_value("CASTAGNOLI", "u32", CASTAGNOLI);
-    crc32.add_array("CASTAGNOLI_TABLE", "u32", &make_table_crc32(CASTAGNOLI));
+    crc32.add_array("CASTAGNOLI_TABLE", "u32", &util::make_table_crc32(CASTAGNOLI));
 
     let IEEE: u32 = 0xedb88320;
     crc32.add_value("IEEE", "u32", IEEE);
-    crc32.add_array("IEEE_TABLE", "u32", &make_table_crc32(IEEE));
+    crc32.add_array("IEEE_TABLE", "u32", &util::make_table_crc32(IEEE));
 
     let KOOPMAN: u32 = 0xeb31d82e;
     crc32.add_value("KOOPMAN", "u32", KOOPMAN);
-    crc32.add_array("KOOPMAN_TABLE", "u32", &make_table_crc32(KOOPMAN));
+    crc32.add_array("KOOPMAN_TABLE", "u32", &util::make_table_crc32(KOOPMAN));
 
     crc32.finish();
 
@@ -58,11 +26,11 @@ fn create_constants() {
 
     let ECMA: u64 = 0xc96c5795d7870f42;
     crc64.add_value("ECMA", "u64", ECMA);
-    crc64.add_array("ECMA_TABLE", "u64", &make_table_crc64(ECMA));
+    crc64.add_array("ECMA_TABLE", "u64", &util::make_table_crc64(ECMA));
 
     let ISO: u64 = 0xd800000000000000;
     crc64.add_value("ISO", "u64", ISO);
-    crc64.add_array("ISO_TABLE", "u64", &make_table_crc64(ISO));
+    crc64.add_array("ISO_TABLE", "u64", &util::make_table_crc64(ISO));
 
     crc64.finish();
 }
@@ -70,4 +38,3 @@ fn create_constants() {
 fn main() {
     create_constants();
 }
-
diff --git a/src/crc32.rs b/src/crc32.rs
index 48302fc..a1de5c7 100644
--- a/src/crc32.rs
+++ b/src/crc32.rs
@@ -3,6 +3,8 @@ use std::hash::Hasher;
 #[cfg(not(feature = "std"))]
 use core::hash::Hasher;
 
+pub use util::make_table_crc32 as make_table;
+
 build_const!("crc32_constants");
 
 pub struct Digest {
@@ -17,22 +19,6 @@ pub trait Hasher32 {
     fn sum32(&self) -> u32;
 }
 
-pub fn make_table(poly: u32) -> [u32; 256] {
-    let mut table = [0u32; 256];
-    for i in 0..256 {
-        let mut value = i as u32;
-        for _ in 0..8 {
-            value = if (value & 1) == 1 {
-                (value >> 1) ^ poly
-            } else {
-                value >> 1
-            }
-        }
-        table[i] = value;
-    }
-    table
-}
-
 pub fn update(mut value: u32, table: &[u32; 256], bytes: &[u8]) -> u32 {
     value = !value;
     for &i in bytes.iter() {
diff --git a/src/crc64.rs b/src/crc64.rs
index 9df484b..6d9b894 100644
--- a/src/crc64.rs
+++ b/src/crc64.rs
@@ -3,6 +3,8 @@ use std::hash::Hasher;
 #[cfg(not(feature = "std"))]
 use core::hash::Hasher;
 
+pub use util::make_table_crc64 as make_table;
+
 build_const!("crc64_constants");
 
 pub struct Digest {
@@ -17,22 +19,6 @@ pub trait Hasher64 {
     fn sum64(&self) -> u64;
 }
 
-pub fn make_table(poly: u64) -> [u64; 256] {
-    let mut table = [0u64; 256];
-    for i in 0..256 {
-        let mut value = i as u64;
-        for _ in 0..8 {
-            value = if (value & 1) == 1 {
-                (value >> 1) ^ poly
-            } else {
-                value >> 1
-            }
-        }
-        table[i] = value;
-    }
-    table
-}
-
 pub fn update(mut value: u64, table: &[u64; 256], bytes: &[u8]) -> u64 {
     value = !value;
     for &i in bytes.iter() {
diff --git a/src/lib.rs b/src/lib.rs
index 2dbe8a6..c04643d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -44,6 +44,7 @@
 
 #[macro_use]
 extern crate build_const;
+extern crate util;
 
 pub mod crc32;
 pub mod crc64;
diff --git a/src/util/Cargo.toml b/src/util/Cargo.toml
new file mode 100644
index 0000000..c30a505
--- /dev/null
+++ b/src/util/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "util"
+version = "0.1.0"
+
+[lib]
+name = "util"
+path = "lib.rs"
diff --git a/src/util/lib.rs b/src/util/lib.rs
new file mode 100644
index 0000000..ec9d617
--- /dev/null
+++ b/src/util/lib.rs
@@ -0,0 +1,33 @@
+//! utility functions shared between source and build script
+
+pub fn make_table_crc32(poly: u32) -> [u32; 256] {
+    let mut table = [0u32; 256];
+    for i in 0..256 {
+        let mut value = i as u32;
+        for _ in 0..8 {
+            value = if (value & 1) == 1 {
+                (value >> 1) ^ poly
+            } else {
+                value >> 1
+            }
+        }
+        table[i] = value;
+    }
+    table
+}
+
+pub fn make_table_crc64(poly: u64) -> [u64; 256] {
+    let mut table = [0u64; 256];
+    for i in 0..256 {
+        let mut value = i as u64;
+        for _ in 0..8 {
+            value = if (value & 1) == 1 {
+                (value >> 1) ^ poly
+            } else {
+                value >> 1
+            }
+        }
+        table[i] = value;
+    }
+    table
+}