{"id":2320,"date":"2019-02-12T14:38:46","date_gmt":"2019-02-12T01:38:46","guid":{"rendered":"http:\/\/www.talkcrypto.org\/blog\/?p=2320"},"modified":"2019-02-20T15:38:34","modified_gmt":"2019-02-20T02:38:34","slug":"remix-mstore-bug","status":"publish","type":"post","link":"https:\/\/www.talkcrypto.org\/blog\/2019\/02\/12\/remix-mstore-bug\/","title":{"rendered":"Remix MSTORE bug"},"content":{"rendered":"\n

I was looking into strings v bytes into a bit more detail and started comparing the gas consumption between them. The following code was used:
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pragma solidity ^0.5.0;
 contract StringVersusByte {
   string constant _string = \"hello\";
   bytes32 constant _bytes = \"hello\";
 function  getAsString() pure public returns(string memory) {
     return _string;
   }
 function  getAsBytes() pure public returns(bytes32) {
     return _bytes;
   }
 }
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After deploying, I executed the the getAsBytes() first and saw that the execution cost was 196 gas.<\/p>\n\n\n\n
\"\"<\/figure><\/div>\n\n\n\n
I then looked to confirm this by stepping through the debugger and summing up the cost of all the op codes.<\/p>\n\n\n\n
<\/div>\n\n\n\n
\"\"<\/figure><\/div>\n\n\n\n
What I discovered was that it summed up to 172 and not 196 gas. I was out by 24 gas. <\/p>\n\n\n\n
I then looked at the debugger and looked at the remaining gas field. It should reduce by the amount of gas but in step 3 it doesn’t. It reduces by 12 instead of 3 as can be seen in the video.<\/p>\n\n\n\n
The culprit opcode is MSTORE and there are 2 MSTORE which makes up the missing 24 gas.<\/p>\n\n\n\n
<\/p>\n\n\n\n
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