mmtk/util/
constants.rs

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/// log2 of the number of bytes in a byte
pub const LOG_BYTES_IN_BYTE: u8 = 0;
/// The number of bytes in a byte
pub const BYTES_IN_BYTE: usize = 1;
/// log2 of the number of bits in a byte
pub const LOG_BITS_IN_BYTE: u8 = 3;
/// The number of bits in a byte
pub const BITS_IN_BYTE: usize = 1 << LOG_BITS_IN_BYTE;

/// log2 of the number of bytes in a gigabyte
pub const LOG_BYTES_IN_GBYTE: u8 = 30;
/// The number of bytes in a gigabyte
pub const BYTES_IN_GBYTE: usize = 1 << LOG_BYTES_IN_GBYTE;

/// log2 of the number of bytes in a megabyte
pub const LOG_BYTES_IN_MBYTE: u8 = 20;
/// The number of bytes in a megabyte
pub const BYTES_IN_MBYTE: usize = 1 << LOG_BYTES_IN_MBYTE;

/// log2 of the number of bytes in a kilobyte
pub const LOG_BYTES_IN_KBYTE: u8 = 10;
/// The number of bytes in a kilobyte
pub const BYTES_IN_KBYTE: usize = 1 << LOG_BYTES_IN_KBYTE;

/// Some card scanning constants ported from Java MMTK.
/// As we haven't implemented card scanning, these are not used at the moment.
mod card_scanning {
    use crate::util::alloc::embedded_meta_data::LOG_BYTES_IN_REGION;

    pub const SUPPORT_CARD_SCANNING: bool = false;
    /// each card consumes four bytes of metadata
    pub const LOG_CARD_META_SIZE: usize = 2;
    /// number of units tracked per card
    pub const LOG_CARD_UNITS: usize = 10;
    /// track at byte grain, save shifting
    pub const LOG_CARD_GRAIN: usize = 0;
    pub const LOG_CARD_BYTES: usize = LOG_CARD_UNITS + LOG_CARD_GRAIN;
    pub const LOG_CARD_META_BYTES: usize =
        LOG_BYTES_IN_REGION - LOG_CARD_BYTES + LOG_CARD_META_SIZE;
    pub const LOG_CARD_META_PAGES: usize = LOG_CARD_META_BYTES - super::LOG_BYTES_IN_PAGE as usize;
    // FIXME: Card scanning is not supported at the moment. Move this to side-metadata in the future.
    pub const CARD_META_PAGES_PER_REGION: usize = if SUPPORT_CARD_SCANNING {
        1 << LOG_CARD_META_PAGES
    } else {
        0
    };
    pub const CARD_MASK: usize = (1 << LOG_CARD_BYTES) - 1;
}
pub(crate) use card_scanning::*;

/// Lazy sweeping - controlled from here because PlanConstraints needs to
/// tell the VM that we need to support linear scan.
// FIXME: we are not really using this constant to decide lazy sweep or not.
pub(crate) const LAZY_SWEEP: bool = true;

// Java-specific sizes currently used by MMTk
// TODO: MMTk should really become independent of these Java types: https://github.com/mmtk/mmtk-core/issues/922
mod java_specific_constants {
    use super::LOG_BITS_IN_BYTE;

    pub const LOG_BYTES_IN_CHAR: u8 = 1;
    pub const BYTES_IN_CHAR: usize = 1 << LOG_BYTES_IN_CHAR;
    pub const LOG_BITS_IN_CHAR: u8 = LOG_BITS_IN_BYTE + LOG_BYTES_IN_CHAR;
    pub const BITS_IN_CHAR: usize = 1 << LOG_BITS_IN_CHAR;

    pub const LOG_BYTES_IN_SHORT: u8 = 1;
    pub const BYTES_IN_SHORT: usize = 1 << LOG_BYTES_IN_SHORT;
    pub const LOG_BITS_IN_SHORT: u8 = LOG_BITS_IN_BYTE + LOG_BYTES_IN_SHORT;
    pub const BITS_IN_SHORT: usize = 1 << LOG_BITS_IN_SHORT;

    pub const LOG_BYTES_IN_INT: u8 = 2;
    pub const BYTES_IN_INT: usize = 1 << LOG_BYTES_IN_INT;
    pub const LOG_BITS_IN_INT: u8 = LOG_BITS_IN_BYTE + LOG_BYTES_IN_INT;
    pub const BITS_IN_INT: usize = 1 << LOG_BITS_IN_INT;

    pub const LOG_BYTES_IN_LONG: u8 = 3;
    pub const BYTES_IN_LONG: usize = 1 << LOG_BYTES_IN_LONG;
    pub const LOG_BITS_IN_LONG: u8 = LOG_BITS_IN_BYTE + LOG_BYTES_IN_LONG;
    pub const BITS_IN_LONG: usize = 1 << LOG_BITS_IN_LONG;

    pub const MAX_INT: usize = i32::MAX as usize; // 0x7fff_ffff
    pub const MIN_INT: usize = i32::MIN as u32 as usize; // 0x8000_0000
}
pub(crate) use java_specific_constants::*;

#[cfg(target_pointer_width = "32")]
/// log2 of the number of bytes in an address
pub const LOG_BYTES_IN_ADDRESS: u8 = 2;
#[cfg(target_pointer_width = "64")]
/// log2 of the number of bytes in an address
pub const LOG_BYTES_IN_ADDRESS: u8 = 3;
/// The number of bytes in an address
pub const BYTES_IN_ADDRESS: usize = 1 << LOG_BYTES_IN_ADDRESS;
/// log2 of the number of bits in an address
pub const LOG_BITS_IN_ADDRESS: usize = LOG_BITS_IN_BYTE as usize + LOG_BYTES_IN_ADDRESS as usize;
/// The number of bits in an address
pub const BITS_IN_ADDRESS: usize = 1 << LOG_BITS_IN_ADDRESS;

/// log2 of the number of bytes in a word
pub const LOG_BYTES_IN_WORD: u8 = LOG_BYTES_IN_ADDRESS;
/// The number of bytes in a word
pub const BYTES_IN_WORD: usize = 1 << LOG_BYTES_IN_WORD;
/// log2 of the number of bits in a word
pub const LOG_BITS_IN_WORD: usize = LOG_BITS_IN_BYTE as usize + LOG_BYTES_IN_WORD as usize;
/// The number of bits in a word
pub const BITS_IN_WORD: usize = 1 << LOG_BITS_IN_WORD;

/// log2 of the number of bytes in a page
pub const LOG_BYTES_IN_PAGE: u8 = 12;
/// The number of bytes in a page
pub const BYTES_IN_PAGE: usize = 1 << LOG_BYTES_IN_PAGE;
/// log2 of the number of bits in a page
pub const LOG_BITS_IN_PAGE: usize = LOG_BITS_IN_BYTE as usize + LOG_BYTES_IN_PAGE as usize;
/// The number of bits in a page
pub const BITS_IN_PAGE: usize = 1 << LOG_BITS_IN_PAGE;

/// log2 of the number of bytes in the address space
pub const LOG_BYTES_IN_ADDRESS_SPACE: u8 = BITS_IN_ADDRESS as u8;

/// log2 of the minimal object size in bytes.
// TODO: this should be VM specific.
pub const LOG_MIN_OBJECT_SIZE: u8 = LOG_BYTES_IN_WORD;
/// The minimal object size in bytes
pub const MIN_OBJECT_SIZE: usize = 1 << LOG_MIN_OBJECT_SIZE;