7 copy

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简介

Copy类操作指的是在EVM中进行不定长的一段数据数据拷贝，例如CALLDATACOPY是一种将calldata中一段数据拷贝到memory中的操作。拷贝以byte作为数据长度单位，注意和栈的U256不同。

由于其长度的不定性，即无法在编写电路时就获知数据拷贝的长度，我们难以在不引入新子电路、子表格的情况下处理此类操作。

我们的做法是，定义了copy子电路，对于Copy类操作，假设其长度为len，在此子电路中，使用len行来处理。每一行都要加上相应的约束来证明是从来源拷贝到去向。对于每次操作，生成的Witness就会包含len行的copy子电路的Row。

具体的，如下操作是Copy类操作：

CODECOPY
CALLDATACOPY
RETURN
RETURNDATACOPY
LOG
调用开始（开始处理一笔交易或者CALL）时，CALLDATA要被写入STATE子电路所维持的状态中。分为两种：
- CALLDATA_FROMPUBLIC 外界（交易、公开数据）的CALLDATA输入
- CALLDATA_FROMCALL 合约调用另一个合约的CALLDATA输入

设计

Witness、Column设计

共使用9列，参见代码。

pub struct Row {
    /// The byte value that is copied
    pub byte: U256,
    /// The source type, one of PublicCalldata, Memory, Bytecode, Calldata, Returndata
    pub src_type: Type,
    /// The source id, tx_idx for PublicCalldata, contract_addr for Bytecode, call_id for Memory, Calldata, Returndata
    pub src_id: U256,
    /// The source pointer, for PublicCalldata, Bytecode, Calldata, Returndata means the index, for Memory means the address
    pub src_pointer: U256,
    /// The source stamp, state stamp for Memory, Calldata, Returndata. None for PublicCalldata and Bytecode
    pub src_stamp: Option<U256>,
    /// The destination type, one of Memory, Calldata, Returndata, PublicLog
    pub dst_type: Type,
    /// The destination id, tx_idx for PublicLog, call_id for Memory, Calldata, Returndata
    pub dst_id: U256,
    /// The destination pointer, for Calldata, Returndata, PublicLog means the index, for Memory means the address
    pub dst_pointer: U256,
    /// The destination stamp, state stamp for Memory, Calldata, Returndata. As for PublicLog it means the log_stamp
    pub dst_stamp: U256,
    /// The counter for one copy operation
    pub cnt: U256,
    /// The length for one copy operation
    pub len: U256,
}

例子：CODECOPY，从bytecode拷贝到memory。例子里长度为8，被拷贝的数据为0xabcd......见下表。

byte	src type	dst type	src id	src pointer	src stamp	dst id	dst pointer	dst stamp	cnt	len
0xab	bytecode=5	memory=0	contract addr	some offset	nil	callid	some mem addr	some stamp	0	8
0xcd	bytecode=5	memory=0	contract addr	some offset	nil	callid	some mem addr	some stamp	1	8
...	bytecode=5	memory=0	contract addr	some offset	nil	callid	some mem addr	some stamp	2	8
	bytecode=5	memory=0	contract addr	some offset	nil	callid	some mem addr	some stamp	3	8
	bytecode=5	memory=0	contract addr	some offset	nil	callid	some mem addr	some stamp	4	8
	bytecode=5	memory=0	contract addr	some offset	nil	callid	some mem addr	some stamp	5	8
	bytecode=5	memory=0	contract addr	some offset	nil	callid	some mem addr	some stamp	6	8
	bytecode=5	memory=0	contract addr	some offset	nil	callid	some mem addr	some stamp	7	8

门约束

TODO

Lookup

每一行，都要进行两个约束，向Copy的来源和Copy的去向进行查找表。查找表的来源都是此子表格的一行（的某些列），去向是“Copy的来源或Copy的去向”。

以上面为例，每一行，要进行：

去向为bytecode的查找表，含义是确定拷贝的数据没错
去向为state（具体tag为memory）的查找表，含义是确定拷贝的数据确实写进去了