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Renamed mask constant and added comment clarifying its use.

This commit is contained in:
Sebastián Claudio Nale 2023-02-16 20:10:45 -03:00
parent 6686116bc0
commit a5fb595cd3
1 changed files with 6 additions and 5 deletions
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11
ethereum/contracts/libraries/external/BytesLib.sol vendored
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@ -10,7 +10,7 @@ pragma solidity >=0.8.0 <0.9.0;
library BytesLib {
uint256 private constant freeMemoryPtr = 0x40;
uint256 private constant mask32ByteAlignment = 0x1f;
uint256 private constant maskModulo32 = 0x1f;
/**
* Size of word read by `mload` instruction.
*/
@ -50,7 +50,7 @@ library BytesLib {
// land at the beginning of the contents of the new array. When
// we're done copying, we overwrite the full first word with
// the actual length of the slice.
let lengthmod := and(length, mask32ByteAlignment)
let lengthmod := and(length, maskModulo32)
// The multiplication in the next line is necessary
// because when slicing multiples of 32 bytes (lengthmod == 0)
// the following copy loop was copying the origin's length
@ -65,9 +65,10 @@ library BytesLib {
src := add(src, memoryWord)
} { mstore(dst, mload(src)) }
//update free-memory pointer
//allocating the array padded to 32 bytes like the compiler does now
mstore(freeMemoryPtr, and(add(dst, mask32ByteAlignment), not(mask32ByteAlignment)))
// Update free-memory pointer
// allocating the array padded to 32 bytes like the compiler does now
// Note that negating bitwise the `maskModulo32` produces a mask that aligns addressing to 32 bytes.
mstore(freeMemoryPtr, and(add(dst, maskModulo32), not(maskModulo32)))
}
//if we want a zero-length slice let's just return a zero-length array
default { mstore(freeMemoryPtr, add(tempBytes, memoryWord)) }