Reference: PodLib primitives

Source: PodLib.sol and bit-width modules PodLib64.sol, PodLib128.sol, PodLib256.sol in @coti-io/coti-contracts.

PodLib is the fast path for built-in private operations on COTI without writing a custom COTI contract. It inherits PodLibBase, which forwards total and callback native fees to IInbox.sendTwoWayMessage.

Network presets

Compose PodLib with a chain preset mixin:

Mixin	Host chain	Source
PodUserSepolia	Ethereum Sepolia (11155111)	PodUserSepolia.sol
PodUserFuji	Avalanche Fuji (43113)	PodUserFuji.sol

Presets call setInbox and configureCoti in their constructor. Your contract only needs:

contract MyApp is PodLib, PodUserSepolia {
    constructor() PodLibBase(msg.sender) {}
}

Network constants (inbox address, COTI chain id, MPC executor) live in PodNetworkConstants.sol. Confirm values against your installed package version.

What PodLib does

• Builds method payloads with MpcAbiCodec

• Routes messages to the configured COTI MPC executor

• Sends two-way Inbox requests with callback and error selectors

• Provides default error handler onDefaultMpcError(bytes32 requestId)

Type mapping: EVM helpers accept it* arguments; COTI executor methods use gt* parameters. The inbox pipeline validates and re-encodes before COTI invocation.

Primitive families (by bit width)

Each helper follows a fee-aware shape:

function add64(
    itUint64 memory a,
    itUint64 memory b,
    address cOwner,
    bytes4 callbackSelector,
    bytes4 errorSelector,
    uint256 totalValueWei,
    uint256 callbackFeeLocalWei
) internal returns (bytes32);

256-bit examples from PodLib256 include:

Category	Functions
Arithmetic	add256, sub256, mul256, mulWrapping256
Bitwise	and256, or256, xor256
Compare	eq256, ne256, ge256, gt256, le256, lt256, min256, max256
Select	mux256
Shift	shl256, shr256
Random	rand256, randBoundedBits256

64- and 128-bit variants mirror the same families on PodLib64 / PodLib128. See the source files for the complete matrix and exact signatures.

Fees

Library sends go through _sendTwoWayWithFee:

• totalValueWei — forwarded as msg.value to the Inbox (entire message budget)

• callbackFeeLocalWei — slice reserved for the callback leg

See How do PoA fees work? for oracle conversion and worked examples.

When to move beyond PodLib

Use custom EVM + COTI contracts when:

• The operation is not a built-in primitive

• The callback payload is a custom tuple

• COTI logic needs multiple private steps and persistent state

See Tutorial: custom privacy logic with PoD and Tutorials: building PoD dApps.

See also

• Reference: data types

• Contract patterns checklist

• Tutorial: private Adder on Sepolia — full walkthrough with TypeScript