Replaced mapping with bitmap

[Havoc19]

Bitmap Token Tracking System

Overview

A bitmap can represent up to 256 tokens using a single uint256 variable, where each bit represents one token:

• 0: Token is not present
• 1: Token is present

How It Works

Bit Positioning

Each token's position is determined by the least significant byte (LSB) of its address:

uint256 bitPos = uint256(uint160(token)) & 0xFF;

This maps each token address to a position between 0-255.

Token Operations

Adding Tokens

To mark a token as present, set its corresponding bit to 1:

tokenBitmap |= 1 << bitPos;

Removing Tokens

To remove a token, clear its bit to 0:

tokenBitmap &= ~(1 << bitPos);

Checking Token Presence

To verify if a token exists in the bitmap:

if (tokenBitmap & (1 << bitPos) != 0) {
    // Token is present
}

Implementation Details

verifyNewTokenList

This method validates new tokens being added:

1. Creates a bitmap for tracking new tokens
2. For each token in newTokens:
   • Verifies non-zero balance
   • Marks token in bitmap
3. Validates each token in _ensoBuyTokens exists in bitmap

updateTokens

This method uses the bitmap for:

1. Creating initial token balance bitmap
2. Removing new tokens from bitmap
3. Checking remaining token balances against dust limits

Technical Notes

• Uses a single uint256 for storage efficiency
• Bitwise operations enable fast token presence checks
• Can track up to 256 unique tokens
• Token positions determined by address LSB