# Dappsys Safe, simple, flexible building-blocks for smart-contract systems.

Auth
`ds-auth` `ds-guard` `ds-roles`
Token
`ds-token` `ds-vault`
Oracle
`ds-cache` `ds-value`
Util
`ds-exec` `ds-math` `ds-note` `ds-proxy` `ds-stop` `ds-thing`
Gov
`ds-multisig`

## DSMath

Safe Arithmetic

DS-Math provides arithmetic functions for the common numerical primitive types of Solidity. You can safely add, subtract, multiply, and divide `uint` numbers without fear of integer overflow. You can also find the minimum and maximum of two numbers.

Additionally, this package provides arithmetic functions for new two higher level numerical concepts called wad (18 decimals) and ray (27 decimals). These are used to represent fixed-point decimal numbers.

A wad is a decimal number with 18 digits of precision and a ray is a decimal number with 27 digits of precision. These functions are necessary to account for the difference between how integer arithmetic behaves normally, and how decimal arithmetic should actually work. A brief example using `wmul`, which returns the product of a wad and another number:

``````1.1 * 2.2 == 2.42

//Regular integer arithmetic adds orders of magnitude:

110 * 220 == 24200

// Wad arithmetic does not add orders of magnitude:

wmul(1.1 ether, 2.2 ether) == 2.42 ether
``````

### Naming Convention

The standard functions are the `uint` set, so their function names are not prefixed: `add`, `sub`, `mul`, `min`, and `max`. There is no `div` function, as divide-by-zero checking is built into the Solidity compiler.

The `int` functions have an `i` prefix: `imin`, and `imax`.

Wad functions have a `w` prefix: `wmul`, `wdiv`.

Ray functions have a `r` prefix: `rmul`, `rdiv`, `rpow`.

### API Reference

#### `add`

Return `x + y` or an exception in case of `uint` overflow.

#### `sub`

Return `x - y` or an exception in case of `uint` overflow.

#### `mul`

Return `x * y` or an exception in case of `uint` overflow.

#### `min`

Return the smaller number of `x` and `y`.

#### `max`

Return the larger number of `x` and `y`.

#### `imin`

Return the smaller number of `x` and `y`.

#### `imax`

Return the larger number of `x` and `y`.

#### `wmul`

Multiply two Wads and return a new Wad with the correct level of precision. A Wad is a decimal number with 18 digits of precision that is being represented as an integer.

#### `wdiv`

Divide two Wads and return a new Wad with the correct level of precision. A Wad is a decimal number with 18 digits of precision that is being represented as an integer.

#### `rmul`

Multiply two Rays and return a new Ray with the correct level of precision. A Ray is a decimal number with 27 digits of precision that is being represented as an integer.

#### `rdiv`

Divide two Rays and return a new Ray with the correct level of precision. A Ray is a decimal number with 27 digits of precision that is being represented as an integer.

#### `rpow`

Raise a Ray to the n^th power and return a new Ray with the correct level of precision. A Ray is a decimal number with 27 digits of precision that is being represented as an integer.

# Tools for dapps

We believe that the free software movement is the most important cultural predecessor to the modern-day renaissance in decentralized technologies.

To catalyze the growth of this ecosystem, and to empower hackers to participate, we’re building a comprehensive suite of blockchain-oriented developer tools in the spirit of the Unix philosophy.

Dapp is all you need to start developing for Ethereum. It creates new dapps, runs Solidity unit tests, debugs, deploys, launches testnets, and more.

Seth is a handy tool for slicing and dicing transactions, querying the blockchain, converting between data formats, performing remote calls, and other everyday tasks.

Hevm is our own EVM implementation with a nimble terminal-based Solidity debugger. It’s used for `dapp test` and `dapp debug`.

## Dappsys - smart contract building blocks

We also maintain Dappsys, an audited collection of smart contract building blocks designed to complement each other. They include;

• `ds-token` — a generic EIP-20 coin;
• `ds-group` — a multisig;
• `ds-guard` — a flexible authority rule;
• `ds-proxy` — a transaction proxy; and
• `ds-cache` — a store of expiring values.

Using these proven parts lets us focus on the novel features of the systems we develop. We share Dappsys to benefit the smart contract ecosystem.