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Add Greg's documentation to MixinErc721Transfer

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This commit is contained in:
Remco Bloemen
2018-06-23 18:03:49 +02:00
committed by Amir Bandeali
parent 562fec01d8
commit 9175b43542
1 changed files with 44 additions and 33 deletions
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77
packages/contracts/src/contracts/current/protocol/AssetProxy/MixinERC721Transfer.sol
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@@ -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