Add deepCopyBytes method to LibBytes

2 files changed, 58 insertions, 0 deletions

diff --git a/packages/contracts/src/contracts/current/test/TestLibBytes/TestLibBytes.sol b/packages/contracts/src/contracts/current/test/TestLibBytes/TestLibBytes.sol
index 5a6801262..b3ed1f620 100644
--- a/packages/contracts/src/contracts/current/test/TestLibBytes/TestLibBytes.sol
+++ b/packages/contracts/src/contracts/current/test/TestLibBytes/TestLibBytes.sol
@@ -25,6 +25,23 @@ contract TestLibBytes is
     LibBytes
 {
 
+    /// @dev Performs a deep copy of a section of a byte array.
+    /// @param b Byte array that will be sliced.
+    /// @param startIndex Index of first byte to copy.
+    /// @param endIndex Index of last byte to copy + 1.
+    /// @return A deep copy of b from startIndex to endIndex.
+    function publicDeepCopyBytes(
+        bytes memory b,
+        uint256 startIndex,
+        uint256 endIndex)
+        public
+        pure
+        returns (bytes memory copy)
+    {
+        copy = deepCopyBytes(b, startIndex, endIndex);
+        return copy;
+    }
+
     /// @dev Tests equality of two byte arrays.
     /// @param lhs First byte array to compare.
     /// @param rhs Second byte array to compare.
diff --git a/packages/contracts/src/contracts/current/utils/LibBytes/LibBytes.sol b/packages/contracts/src/contracts/current/utils/LibBytes/LibBytes.sol
index 975565773..527f7a7a9 100644
--- a/packages/contracts/src/contracts/current/utils/LibBytes/LibBytes.sol
+++ b/packages/contracts/src/contracts/current/utils/LibBytes/LibBytes.sol
@@ -21,9 +21,50 @@ pragma solidity ^0.4.24;
 contract LibBytes {
 
     // Revert reasons
+    string constant GT_ZERO_LENGTH_REQUIRED = "Length must be greater than 0.";
     string constant GTE_4_LENGTH_REQUIRED = "Length must be greater than or equal to 4.";
     string constant GTE_20_LENGTH_REQUIRED = "Length must be greater than or equal to 20.";
     string constant GTE_32_LENGTH_REQUIRED = "Length must be greater than or equal to 32.";
+    string constant INDEX_OUT_OF_BOUNDS = "Specified array index is out of bounds.";
+
+    /// @dev Performs a deep copy of a section of a byte array.
+    /// @param b Byte array that will be copied.
+    /// @param index Index of first byte to copy.
+    /// @param len Number of bytes to copy starting from index.
+    /// @return A deep copy `len` bytes of b starting from index.
+    function deepCopyBytes(
+        bytes memory b,
+        uint256 index,
+        uint256 len)
+        internal
+        pure
+        returns (bytes memory)
+    {
+        require(
+            len > 0,
+            GT_ZERO_LENGTH_REQUIRED
+        );
+        require(
+            b.length >= index + len,
+            INDEX_OUT_OF_BOUNDS
+        );
+
+        bytes memory copy = new bytes(len);
+
+        // Arrays are prefixed by a 256 bit length parameter
+        index += 32;
+
+        assembly {
+            // Start storing onto copy after length field
+            let storeStartIndex := add(copy, 32)
+            // Start loading from b at index
+            let startLoadIndex := add(b, index)
+            for {let i := 0} lt(i, len) {i := add(i, 32)} {
+                mstore(add(storeStartIndex, i), mload(add(startLoadIndex, i)))
+            }
+        }
+        return copy;
+    }
 
     /// @dev Tests equality of two byte arrays.
     /// @param lhs First byte array to compare.