EVM: Add pct to Mimic helper

packages/evm/contracts/utils/MimicHelper.sol

@@ -14,11 +14,16 @@
 
 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
  */
 contract MimicHelper {
+    // Basis points scale
+    uint16 internal constant BPS_SCALE = 10_000;
+
     // Custom byte storage per user and key
     mapping (address => mapping (string => bytes)) internal _customStorage;
 
@@ -27,6 +32,11 @@ contract MimicHelper {
      */
     event StorageSet(address indexed user, string indexed key, bytes indexed data);
 
+    /**
+     * @dev A single percent is greater than 10_000 basis points
+     */
+    error MimicHelperInvalidPercent();
+
     /**
      * @dev Tells the native token balance of an address
      * @param target Address to get native token balance
@@ -61,4 +71,14 @@ contract MimicHelper {
         _customStorage[msg.sender][key] = data;
         emit StorageSet(msg.sender, key, data);
     }
+
+    /**
+     * @dev Tells a percentage of an amount, rounding down
+     * @param amount Amount to compute the percentage of
+     * @param percent Percentage to apply, expressed in basis points. 10_000 = 100%, 50 = 0.5%
+     */
+    function pct(uint256 amount, uint16 percent) external pure returns (uint256) {
+        if (percent > BPS_SCALE) revert MimicHelperInvalidPercent();
+        return Math.mulDiv(amount, percent, BPS_SCALE);
+    }
 }

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

@@ -116,4 +116,48 @@ describe('MimicHelper', () => {
       })
     })
   })
+
+  describe('pct', () => {
+    const BPS_SCALE = 10_000
+
+    context('when the percent is between 0 and 10_000', () => {
+      context('when amount is not 0', () => {
+        const amount = 101n
+
+        it('returns the percentage rounding down', async () => {
+          expect(await mimicHelper.pct(amount, 0)).to.be.equal(0n)
+          expect(await mimicHelper.pct(amount, 50)).to.be.equal(0n)
+          expect(await mimicHelper.pct(amount, 100)).to.be.equal(1n)
+          expect(await mimicHelper.pct(amount, 5000)).to.be.equal(50n)
+          expect(await mimicHelper.pct(amount, BPS_SCALE)).to.be.equal(amount)
+        })
+
+        it('always rounds down', async () => {
+          expect(await mimicHelper.pct(1, 9900)).to.equal(0n)
+          expect(await mimicHelper.pct(3, 3333)).to.equal(0n)
+          expect(await mimicHelper.pct(3, 3334)).to.equal(1n)
+          expect(await mimicHelper.pct(4, 3333)).to.equal(1n)
+          expect(await mimicHelper.pct(99, 3300)).to.equal(32n)
+          expect(await mimicHelper.pct(100, 3300)).to.equal(33n)
+        })
+      })
+
+      context('when amount is 0', () => {
+        it('returns 0', async () => {
+          expect(await mimicHelper.pct(0, 0)).to.equal(0n)
+          expect(await mimicHelper.pct(0, 5000)).to.equal(0n)
+          expect(await mimicHelper.pct(0, BPS_SCALE)).to.equal(0n)
+        })
+      })
+    })
+
+    context('when the percent is greater than 10_000', () => {
+      it('reverts', async () => {
+        await expect(mimicHelper.pct(1, BPS_SCALE + 1)).to.be.revertedWithCustomError(
+          mimicHelper,
+          'MimicHelperInvalidPercent'
+        )
+      })
+    })
+  })
 })