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Fix some issues regarding checked arithmethics in stringutils

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This commit is contained in:
Alex Beregszaszi 2021-04-24 01:22:13 +01:00
parent 6b3357be50
commit 5331bc679a
2 changed files with 23 additions and 14 deletions
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13
test/libsolidity/semanticTests/externalContracts/_stringutils/stringutils.sol
View File

@ -52,8 +52,15 @@ library strings {
src += 32;
}
// The following masking would overflow in the case of len=0
// and the code path in that case is useless, albeit correct.
// This shortcut avoids it and saves gas.
if (len == 0)
return;
// Copy remaining bytes
uint mask = 256 ** (32 - len) - 1;
uint mask;
unchecked { mask = 256 ** (32 - len) - 1; }
assembly {
let srcpart := and(mload(src), not(mask))
let destpart := and(mload(dest), mask)
@ -215,7 +222,9 @@ library strings {
if(shortest < 32) {
mask = ~(2 ** (8 * (32 - shortest + idx)) - 1);
}
uint256 diff = (a & mask) - (b & mask);
uint256 diff;
// This depends on potential underflow.
unchecked { diff = (a & mask) - (b & mask); }
if (diff != 0)
return int(diff);
}

24
test/libsolidity/semanticTests/externalContracts/strings.sol
View File

@ -51,26 +51,26 @@ contract test {
// compileViaYul: also
// ----
// constructor()
// gas irOptimized: 926170
// gas legacy: 1192776
// gas legacyOptimized: 777238
// gas irOptimized: 912777
// gas legacy: 1188228
// gas legacyOptimized: 771634
// toSlice(string): 0x20, 11, "hello world" -> 11, 0xa0
// gas irOptimized: 22877
// gas legacy: 23190
// gas legacyOptimized: 22508
// roundtrip(string): 0x20, 11, "hello world" -> 0x20, 11, "hello world"
// gas irOptimized: 23783
// gas legacy: 24560
// gas legacyOptimized: 23481
// gas irOptimized: 23676
// gas legacy: 23820
// gas legacyOptimized: 23123
// utf8len(string): 0x20, 16, "\xf0\x9f\x98\x83\xf0\x9f\x98\x83\xf0\x9f\x98\x83\xf0\x9f\x98\x83" -> 4 # Input: "😃😃😃😃" #
// gas irOptimized: 24779
// gas legacy: 25716
// gas legacyOptimized: 24115
// multiconcat(string,uint256): 0x40, 3, 11, "hello world" -> 0x20, 0x58, 0x68656c6c6f20776f726c6468656c6c6f20776f726c6468656c6c6f20776f726c, 0x6468656c6c6f20776f726c6468656c6c6f20776f726c6468656c6c6f20776f72, 49027192869463622675296414541903001712009715982962058146354235762728281047040 # concatenating 3 times #
// gas irOptimized: 30478
// gas legacy: 36801
// gas legacyOptimized: 30420
// benchmark(string,bytes32): 0x40, 0x0842021, 8, "solidity" -> FAILURE, hex"4e487b71", 0x11
// gas irOptimized: 27298
// gas irOptimized: 29729
// gas legacy: 31621
// gas legacyOptimized: 27668
// gas legacyOptimized: 27914
// benchmark(string,bytes32): 0x40, 0x0842021, 8, "solidity" -> 0x2020
// gas irOptimized: 2903627
// gas legacy: 4381235
// gas legacyOptimized: 2317529