EVM: Add pct to MimicHelper

packages/evm/contracts/utils/MimicHelper.sol

@@ -14,6 +14,8 @@
 
 pragma solidity ^0.8.20;
 
+import { Math } from '@openzeppelin/contracts/utils/math/Math.sol';
+
 /**
  * @title Mimic Helper
  * @dev Collection of helper functions for the Mimic Protocol
@@ -27,6 +29,16 @@ contract MimicHelper {
      */
     event StorageSet(address indexed user, string indexed key, bytes indexed data);
 
+    /**
+     * @dev The percents add up to 100 or more
+     */
+    error MimicHelperInvalidPercent();
+
+    /**
+     * @dev The percents array is empty
+     */
+    error MimicHelperEmptyPercents();
+
     /**
      * @dev Tells the native token balance of an address
      * @param target Address to get native token balance
@@ -61,4 +73,30 @@ contract MimicHelper {
         _customStorage[msg.sender][key] = data;
         emit StorageSet(msg.sender, key, data);
     }
+
+    /**
+     * @dev Splits an amount by specified percentages.
+     * All remainder goes to the last split.
+     * @param amount Amount to be split
+     * @param percents Array of percents
+     * @return splits Array of `percents.length + 1` amounts; the last element holds the remainder
+     */
+    function pct(uint256 amount, uint8[] calldata percents) external pure returns (uint256[] memory splits) {
+        uint256 len = percents.length;
+        if (len == 0) revert MimicHelperEmptyPercents();
+
+        splits = new uint256[](len + 1);
+        uint256 pctSum = 0;
+        uint256 amountSum = 0;
+
+        for (uint256 i = 0; i < len; i++) {
+            splits[i] = Math.mulDiv(amount, percents[i], 100);
+            amountSum += splits[i];
+            pctSum += percents[i];
+        }
+        if (pctSum >= 100) revert MimicHelperInvalidPercent();
+
+        splits[len] = amount - amountSum; // absorbs rounding dust; never underflows since pctSum < 100
+        return splits;
+    }
 }

packages/evm/test/utils/MimicHelper.test.ts

@@ -116,4 +116,59 @@ describe('MimicHelper', () => {
       })
     })
   })
+
+  describe('pct', () => {
+    context('when the percents leave a remainder', () => {
+      const amount = 101n
+      const percents = [50]
+
+      it('returns splits that add up to the total', async () => {
+        const splits = await mimicHelper.pct(amount, percents)
+
+        expect(splits).to.have.lengthOf(percents.length + 1)
+        expect(splits[0]).to.be.equal(50n)
+        expect(splits[1]).to.be.equal(51n)
+        expect(splits.reduce((total, split) => total + split, 0n)).to.be.equal(amount)
+      })
+    })
+
+    context('when there are multiple percents', () => {
+      const amount = 100n
+      const percents = [30, 30]
+
+      it('returns a split per percent plus the remainder', async () => {
+        const splits = await mimicHelper.pct(amount, percents)
+
+        expect(splits).to.have.lengthOf(percents.length + 1)
+        expect(splits[0]).to.be.equal(30n)
+        expect(splits[1]).to.be.equal(30n)
+        expect(splits[2]).to.be.equal(40n)
+        expect(splits.reduce((total, split) => total + split, 0n)).to.be.equal(amount)
+      })
+    })
+
+    context('when the percents sum to 100% or more', () => {
+      const amount = 101n
+      const percents = [50, 50]
+
+      it('reverts', async () => {
+        await expect(mimicHelper.pct(amount, percents)).to.be.revertedWithCustomError(
+          mimicHelper,
+          'MimicHelperInvalidPercent'
+        )
+      })
+    })
+
+    context('when the percents array is empty', () => {
+      const amount = 101n
+      const percents: number[] = []
+
+      it('reverts', async () => {
+        await expect(mimicHelper.pct(amount, percents)).to.be.revertedWithCustomError(
+          mimicHelper,
+          'MimicHelperEmptyPercents'
+        )
+      })
+    })
+  })
 })