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authorRemco Bloemen <remco@wicked.ventures>2018-06-24 00:03:49 +0800
committerAmir Bandeali <abandeali1@gmail.com>2018-06-26 07:19:07 +0800
commit9175b43542a8797b0eb3c24e8188ebac67242733 (patch)
treebbc608c1b41201908ea47b750d5ebe48434a494e
parent562fec01d89cae43b813e0f22ffe924953d5fadc (diff)
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Add Greg's documentation to MixinErc721Transfer
-rw-r--r--packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC721Transfer.sol77
1 files changed, 44 insertions, 33 deletions
diff --git a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC721Transfer.sol b/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC721Transfer.sol
index af986adfa..c170917ea 100644
--- a/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC721Transfer.sol
+++ b/packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC721Transfer.sol
@@ -27,7 +27,9 @@ contract MixinERC721Transfer is
LibTransferErrors
{
using LibBytes for bytes;
- bytes4 constant SAFE_TRANSFER_FROM_SELECTOR = bytes4(keccak256("safeTransferFrom(address,address,uint256,bytes)"));
+
+ bytes4 constant SAFE_TRANSFER_FROM_SELECTOR = bytes4(keccak256("safeTransferFrom(address,address,uint256,bytes)"));
+
/// @dev Internal version of `transferFrom`.
/// @param assetData Encoded byte array.
/// @param from Address to transfer asset from.
@@ -57,44 +59,54 @@ contract MixinERC721Transfer is
// We construct calldata for the `token.safeTransferFrom` ABI.
// The layout of this calldata is in the table below.
//
- // | Area | Offset | Length | Contents |
- // | -------- |--------|---------|-------------------------------------------- |
- // | Header | 0 | 4 | function selector |
- // | Params | | 4 * 32 | function parameters: |
- // | | 4 | | 1. from |
- // | | 36 | | 2. to |
- // | | 68 | | 3. tokenId |
- // | | 100 | | 4. offset to receiverData (*) |
- // | Data | | | receiverData: |
- // | | 132 | 32 | receiverData Length |
- // | | 164 | ** | receiverData Contents |
+ // | Area | Offset | Length | Contents |
+ // |----------|--------|---------|-------------------------------------|
+ // | Header | 0 | 4 | function selector |
+ // | Params | | 4 * 32 | function parameters: |
+ // | | 4 | | 1. from |
+ // | | 36 | | 2. to |
+ // | | 68 | | 3. tokenId |
+ // | | 100 | | 4. offset to receiverData (*) |
+ // | Data | | | receiverData: |
+ // | | 132 | 32 | receiverData Length |
+ // | | 164 | ** | receiverData Contents |
bytes4 safeTransferFromSelector = SAFE_TRANSFER_FROM_SELECTOR;
bool success;
assembly {
/////// Setup State ///////
- // `cdStart` is the start of the calldata for `token.safeTransferFrom` (equal to free memory ptr).
+ // `cdStart` is the start of the calldata for
+ // `token.safeTransferFrom` (equal to free memory ptr).
let cdStart := mload(64)
- // `dataAreaLength` is the total number of words needed to store `receiverData`
- // As-per the ABI spec, this value is padded up to the nearest multiple of 32,
- // and includes 32-bytes for length.
- // It's calculated as folows:
+ // `dataAreaLength` is the total number of words
+ // needed to store `receiverData`
+ // As-per the ABI spec, this value is padded up to
+ // the nearest multiple of 32,
+ // and includes 32-bytes for length.
+ // It's calculated as folows:
// - Unpadded length in bytes = `mload(receiverData) + 32`
- // - Add 31 to this value then divide by 32 to get the length in words.
- // - Multiply this value by 32 to get the padded length in bytes.
- let dataAreaLength := mul(div(add(mload(receiverData), 63), 32), 32)
+ // - Add 31 to convert rounding down to rounding up.
+ // Combined with the previous and this is `63`.
+ // - Round down to nearest multiple of 32 by clearing
+ // bits 0x1F. This is done with `and` and a mask.
+ let dataAreaLength := and(add(mload(receiverData), 63), 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFE0)
// `cdEnd` is the end of the calldata for `token.safeTransferFrom`.
let cdEnd := add(cdStart, add(132, dataAreaLength))
/////// Setup Header Area ///////
// This area holds the 4-byte `transferFromSelector`.
+ // Any trailing data in transferFromSelector will be
+ // overwritten in the next `mstore` call.
mstore(cdStart, safeTransferFromSelector)
/////// Setup Params Area ///////
- // Each parameter is padded to 32-bytes. The entire Params Area is 128 bytes.
+ // Each parameter is padded to 32-bytes.
+ // The entire Params Area is 128 bytes.
// Notes:
- // 1. A 20-byte mask is applied to addresses to zero-out the unused bytes.
- // 2. The offset to `receiverData` is the length of the Params Area (128 bytes).
+ // 1. A 20-byte mask is applied to addresses
+ // to zero-out the unused bytes.
+ // 2. The offset to `receiverData` is the length
+ // of the Params Area (128 bytes).
mstore(add(cdStart, 4), and(from, 0xffffffffffffffffffffffffffffffffffffffff))
mstore(add(cdStart, 36), and(to, 0xffffffffffffffffffffffffffffffffffffffff))
mstore(add(cdStart, 68), tokenId)
@@ -108,19 +120,18 @@ contract MixinERC721Transfer is
dataArea := add(dataArea, 32)
receiverData := add(receiverData, 32)
}
-
- /////// Call `token.safeTransferFrom` using the constructed calldata ///////
+
+ /////// Call `token.safeTransferFrom` using the calldata ///////
success := call(
- gas,
- token,
- 0,
- cdStart,
- sub(cdEnd, cdStart),
- cdStart,
- 0
+ gas, // forward all gas
+ token, // call address of token contract
+ 0, // don't send any ETH
+ cdStart, // pointer to start of input
+ sub(cdEnd, cdStart), // length of input
+ cdStart, // write output over input
+ 0 // output size is 0 bytes
)
}
-
require(
success,
TRANSFER_FAILED