plonky2/evm/src/cpu/kernel/global_metadata.rs

/// These metadata fields contain global VM state, stored in the `Segment::Metadata` segment of the
/// kernel's context (which is zero).
#[derive(Copy, Clone, Eq, PartialEq, Hash, Ord, PartialOrd, Debug)]
pub(crate) enum GlobalMetadata {
    /// The largest context ID that has been used so far in this execution. Tracking this allows us
    /// give each new context a unique ID, so that its memory will be zero-initialized.
    LargestContext = 0,
    /// The address of the sender of the transaction.
    Origin = 1,
    /// The size of active memory, in bytes.
    MemorySize = 2,
}

impl GlobalMetadata {
    pub(crate) const COUNT: usize = 3;

    pub(crate) fn all() -> [Self; Self::COUNT] {
        [Self::LargestContext, Self::Origin, Self::MemorySize]
    }

    /// The variable name that gets passed into kernel assembly code.
    pub(crate) fn var_name(&self) -> &'static str {
        match self {
            GlobalMetadata::LargestContext => "GLOBAL_METADATA_LARGEST_CONTEXT",
            GlobalMetadata::Origin => "GLOBAL_METADATA_ORIGIN",
            GlobalMetadata::MemorySize => "GLOBAL_METADATA_MEMORY_SIZE",
        }
    }
}