如何在huff中返回常数变量

Question

假设我在愤怒中有一个常数变量：

#define constant myAddress = 0x0000000000000000000000000000000000000000

我将如何制作一个宏来读取它？因为它没有储存槽，所以我不会用.

#define macro GET_ADDRESS() = takes (0) returns (0) {
    // No storage slot
    [VALUE_LOCATION]   
    sload                

    0x00 mstore
    0x20 0x00 return
}

Answer 1

当您想要将一个常量推送到堆栈时，您可以使用括号语法[MY_CONST] &编译器将插入PUSH<N> value，其中N=该常数的值中的字节数。

将常量推到堆栈后，可以使用0x20 0x00 return返回32个字节

#define macro GET_ADDRESS() = takes (0) returns (0) {
    [PRICE_FEED_ADDRESS] 0x00 mstore
    0x20 0x00 return
}

只返回常量作为视图函数的完整示例代码：

// SPDX-License-Identifier: MIT

/* Interface */
#define function getAddress() view returns (address)

/* Constants */
#define constant MY_CONST_ADDRESS = 0x0000000000000000000000000000000000000001 


/* Macrocs (Functions) */
#define macro GET_ADDRESS() = takes (0) returns (0) {
    [MY_CONST_ADDRESS] 0x00 mstore
    0x20 0x00 return
}


#define macro MAIN() = takes (0) returns (0) {
    // Identify which function is being called.
    0x00 calldataload 0xE0 shr

    // We tell our code where to go based on the function selector
    // 0x38cc4831 is the function selector of `getAddress`
    // Here is some info on quickly getting a func selector: https://ethereum.stackexchange.com/questions/131693/fastest-way-to-find-the-function-in-a-contract-from-its-selector
    dup1 0x38cc4831 eq getAddress jumpi 

    getAddress:
        GET_ADDRESS()
}