ceil32

ceil32 is a helper commonly used in Ethereum smart contract development. It returns the smallest multiple of 32 that is greater than or equal to a given unsigned integer x. In simple terms, ceil32(x) rounds x up to the next 32-byte boundary. The mathematical expression is often written as ceil32(x) = (x + 31) / 32 * 32, or equivalently: if x is already a multiple of 32, return x; otherwise add the difference to reach the next multiple of 32.

The function is tied to the memory model of the Ethereum Virtual Machine, which operates on 32-byte words. ceil32 is used to determine how much memory to allocate for values of dynamic length (such as bytes or strings) or for ABI encoding of complex types. By aligning data to 32-byte boundaries, developers help ensure that reads and copies operate on whole words, which can simplify memory management and improve predictability of gas costs. It is a high-level utility rather than an EVM opcode.

In practice, ceil32 is implemented in Solidity and other toolchains as a small pure function. Common implementations compute either (x + 31) / 32 * 32 or, more explicitly, check the remainder of x modulo 32 and return x if the remainder is zero, or x plus (32 minus the remainder) if not. Many libraries define ceil32 as a reusable function used whenever buffers or memory layouts require 32-byte alignment.