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The Precision Challenge

Cosmos SDK and Ethereum use different decimal precisions for their native tokens:
  • Cosmos SDK: 6 decimals (1 ATOM = 10^6 uatom)
  • Ethereum: 18 decimals (1 ETH = 10^18 wei)
This 12-decimal difference creates challenges when bridging the two ecosystems. Simply scaling values would lose precision or create rounding errors.

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PreciseBank Solution

The PreciseBank module solves this by decomposing balances into integer and fractional components: 
Total Balance (18 decimals) = Integer Part (6 decimals) × 10^12 + Fractional Part
For any account with balance a(n) in smallest units: 
a(n) = b(n) × 10^12 + f(n)
Where:
  • a(n) = Total balance in 18-decimal units (atest)
  • b(n) = Integer balance in 6-decimal units (uatom) - stored in x/bank
  • f(n) = Fractional balance (remainder) - stored in x/precisebank
  • Constraint: 0 ≤ f(n) < 10^12

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Example

Balance of 1,234,567,890,123,456,789 atest decomposes to: 
1,234,567,890,123,456,789 = 1,234,567 × 10^12 + 890,123,456,789

Where:
- b(n) = 1,234,567 uatom (stored in x/bank)
- f(n) = 890,123,456,789 atest (stored in x/precisebank)
- Total = 1.234567890123456789 ATOM

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Reserve Backing

A module reserve account maintains supply consistency: 
Reserve Balance × 10^12 = Sum of All Fractional Balances + Remainder
This ensures the fundamental invariant: 
Total Supply (18-decimal) = Bank Supply (6-decimal) × 10^12
The reserve holds integer units to back all fractional amounts in circulation.

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Implementation

Storage:
  • 6-decimal amounts stored in existing bank module
  • Only fractional remainders stored separately in precisebank
  • Full 18-decimal precision reconstructed on query
Query Performance: 
fullBalance = bankBalance × 10^12 + fractionalBalance
Operations: Transfer, mint, and burn operations automatically handle carry/borrow between integer and fractional parts.

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Why This Approach

Backward Compatibility: Existing bank module continues to work unchanged for non-EVM operations. Storage Efficiency: Only stores fractional amounts when needed, not full 18-decimal balances for every account. Precision Guarantee: No rounding or precision loss - every atest is tracked accurately. Performance: Single multiplication and addition reconstructs full precision without expensive arbitrary-precision math.