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Optimize Math operations using branchless bool to uint translation. #4878

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Merged
merged 10 commits into from
Feb 7, 2024
Merged

Optimize Math operations using branchless bool to uint translation. #4878

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7f5b1b3
Make Math.log2 branchless
CodeSandwich Feb 5, 2024
7523995
add Math.boolToUint
Amxx Feb 6, 2024
45bbe87
branchless rounding
Amxx Feb 6, 2024
c8e9e3c
Make boolToUint clean the upper bits
CodeSandwich Feb 6, 2024
32b3d97
Make log2 more readable
CodeSandwich Feb 6, 2024
8417107
Update .changeset/nervous-pans-grow.md
Amxx Feb 6, 2024
3ae1b4a
Move `boolToUint` to `SafeCast`
ernestognw Feb 6, 2024
f8cb792
Update .changeset/nervous-pans-grow.md
ernestognw Feb 6, 2024
a371515
fix generation
Amxx Feb 6, 2024
b0ad358
Merge branch 'master' into optimize_log2
Amxx Feb 7, 2024
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5 changes: 5 additions & 0 deletions .changeset/nervous-pans-grow.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'openzeppelin-solidity': patch
---

Make Math.log2 branchless
110 changes: 60 additions & 50 deletions contracts/utils/math/Math.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -393,38 +393,38 @@ library Math {
*/
function log2(uint256 value) internal pure returns (uint256) {
uint256 result = 0;
uint256 isGt;
unchecked {
if (value >> 128 > 0) {
value >>= 128;
result += 128;
}
if (value >> 64 > 0) {
value >>= 64;
result += 64;
}
if (value >> 32 > 0) {
value >>= 32;
result += 32;
}
if (value >> 16 > 0) {
value >>= 16;
result += 16;
}
if (value >> 8 > 0) {
value >>= 8;
result += 8;
}
if (value >> 4 > 0) {
value >>= 4;
result += 4;
}
if (value >> 2 > 0) {
value >>= 2;
result += 2;
}
if (value >> 1 > 0) {
result += 1;
}
isGt = boolToUint(value > 0xffffffffffffffffffffffffffffffff);
value >>= isGt * 128;
result += isGt * 128;

isGt = boolToUint(value > 0xffffffffffffffff);
value >>= isGt * 64;
result += isGt * 64;

isGt = boolToUint(value > 0xffffffff);
value >>= isGt * 32;
result += isGt * 32;

isGt = boolToUint(value > 0xffff);
value >>= isGt * 16;
result += isGt * 16;

isGt = boolToUint(value > 0xff);
value >>= isGt * 8;
result += isGt * 8;

isGt = boolToUint(value > 0xf);
value >>= isGt * 4;
result += isGt * 4;

isGt = boolToUint(value > 0x3);
value >>= isGt * 2;
result += isGt * 2;

isGt = boolToUint(value > 0x1);
result += isGt;
}
return result;
}
Expand Down Expand Up @@ -497,26 +497,26 @@ library Math {
*/
function log256(uint256 value) internal pure returns (uint256) {
uint256 result = 0;
uint256 isGt;
unchecked {
if (value >> 128 > 0) {
value >>= 128;
result += 16;
}
if (value >> 64 > 0) {
value >>= 64;
result += 8;
}
if (value >> 32 > 0) {
value >>= 32;
result += 4;
}
if (value >> 16 > 0) {
value >>= 16;
result += 2;
}
if (value >> 8 > 0) {
result += 1;
}
isGt = boolToUint(value > 0xffffffffffffffffffffffffffffffff);
value >>= isGt * 128;
result += isGt * 16;

isGt = boolToUint(value > 0xffffffffffffffff);
value >>= isGt * 64;
result += isGt * 8;

isGt = boolToUint(value > 0xffffffff);
value >>= isGt * 32;
result += isGt * 4;

isGt = boolToUint(value > 0xffff);
value >>= isGt * 16;
result += isGt * 2;

isGt = boolToUint(value > 0xff);
result += isGt;
}
return result;
}
Expand All @@ -538,4 +538,14 @@ library Math {
function unsignedRoundsUp(Rounding rounding) internal pure returns (bool) {
return uint8(rounding) % 2 == 1;
}

/**
* @dev Cast a boolean (false or true) to a uint256 (0 or 1) with no jump.
*/
function boolToUint(bool b) internal pure returns (uint256 u) {
/// @solidity memory-safe-assembly
assembly {
u := b
}
}
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@ernestognw ernestognw Feb 6, 2024

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This looks to me more of a fit into the SafeCast library with the function toUint(bool b) signature as it already requires a boolean as an argument.

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@CodeSandwich CodeSandwich Feb 6, 2024 •
edited
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I'm totally fine with this, but does it fit the other functions from SafeCast? IIUC the main goal of this library is to make dangerous operations and throw in case of an overflow. In toUint256(bool) there's no overflow possible, there's nothing "safe" about this SafeCast function.

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@ernestognw ernestognw Feb 6, 2024

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Yeah that's right, I don't have the last word but I feel confident that SafeCast is a better fit than Math.

We might consider having these unconventional casts in a different library but that's a broader discussion.

}
10 changes: 10 additions & 0 deletions test/utils/math/Math.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -512,4 +512,14 @@ describe('Math', function () {
});
});
});

describe('boolToUint', function () {
it('boolToUint(false) should be 0', async function () {
expect(await this.mock.$boolToUint(false)).to.equal(0n);
});

it('boolToUint(true) should be 1', async function () {
expect(await this.mock.$boolToUint(true)).to.equal(1n);
});
});
});