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Clarify non-zero hashes.

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This commit is contained in:
Stephen Chung 2021-12-06 10:34:13 +08:00
parent 54f78c5cd9
commit 206b5051eb
3 changed files with 34 additions and 24 deletions
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12
src/ast.rs
View File

@ -1,7 +1,7 @@
//! Module defining the AST (abstract syntax tree).
use crate::calc_fn_hash;
use crate::func::hashing::DEFAULT_HASH;
use crate::func::hashing::ALT_ZERO_HASH;
use crate::module::NamespaceRef;
use crate::tokenizer::Token;
use crate::types::dynamic::Union;
@ -1800,7 +1800,7 @@ impl OpAssignment<'_> {
/// to possible function overloading for different parameter types.
#[derive(Clone, Copy, Eq, PartialEq, Hash, Default)]
pub struct FnCallHashes {
/// Pre-calculated hash for a script-defined function ([`None`] if native functions only).
/// Pre-calculated hash for a script-defined function (zero if native functions only).
#[cfg(not(feature = "no_function"))]
pub script: u64,
/// Pre-calculated hash for a native Rust function with no parameter types.
@ -1825,7 +1825,7 @@ impl fmt::Debug for FnCallHashes {
impl From<u64> for FnCallHashes {
#[inline(always)]
fn from(hash: u64) -> Self {
let hash = if hash == 0 { DEFAULT_HASH } else { hash };
let hash = if hash == 0 { ALT_ZERO_HASH } else { hash };
Self {
#[cfg(not(feature = "no_function"))]
@ -1843,7 +1843,7 @@ impl FnCallHashes {
Self {
#[cfg(not(feature = "no_function"))]
script: 0,
native: if hash == 0 { DEFAULT_HASH } else { hash },
native: if hash == 0 { ALT_ZERO_HASH } else { hash },
}
}
/// Create a [`FnCallHashes`] with both native Rust and script function hashes.
@ -1852,8 +1852,8 @@ impl FnCallHashes {
pub const fn from_all(#[cfg(not(feature = "no_function"))] script: u64, native: u64) -> Self {
Self {
#[cfg(not(feature = "no_function"))]
script: if script == 0 { DEFAULT_HASH } else { script },
native: if native == 0 { DEFAULT_HASH } else { native },
script: if script == 0 { ALT_ZERO_HASH } else { script },
native: if native == 0 { ALT_ZERO_HASH } else { native },
}
}
/// Is this [`FnCallHashes`] native Rust only?

27
src/func/hashing.rs
View File

@ -8,13 +8,24 @@ use std::{
iter::empty,
};
pub const DEFAULT_HASH: u64 = 42;
/// Dummy hash value to map zeros to. This value can be anything.
///
/// # Notes
///
/// Hashes are `u64`, and they can be zero (although extremely unlikely).
/// It is possible to hijack the zero value to indicate non-existence,
/// like [`None`] in [`Option<u64>`].
///
/// When a hash is calculated to be zero, it gets mapped to this alternate hash value.
/// This has the effect of releasing the zero value at the expense of causing the probability of
/// this value to double, which has minor impacts.
pub const ALT_ZERO_HASH: u64 = 42;
/// A hasher that only takes one single [`u64`] and returns it as a non-zero hash key.
///
/// # Zeros
///
/// If the value is zero, then it is mapped to `DEFAULT_HASH`.
/// If the value is zero, it is mapped to `ALT_ZERO_HASH`.
///
/// # Panics
///
@ -37,7 +48,7 @@ impl Hasher for StraightHasher {
self.0 = u64::from_ne_bytes(key);
if self.0 == 0 {
self.0 = DEFAULT_HASH
self.0 = ALT_ZERO_HASH
}
}
}
@ -51,7 +62,7 @@ impl BuildHasher for StraightHasherBuilder {
#[inline(always)]
fn build_hasher(&self) -> Self::Hasher {
StraightHasher(DEFAULT_HASH)
StraightHasher(ALT_ZERO_HASH)
}
}
@ -92,7 +103,7 @@ pub fn calc_qualified_var_hash<'a>(
var_name.as_ref().hash(s);
match s.finish() {
0 => DEFAULT_HASH,
0 => ALT_ZERO_HASH,
r => r,
}
}
@ -130,7 +141,7 @@ pub fn calc_qualified_fn_hash(
num.hash(s);
match s.finish() {
0 => DEFAULT_HASH,
0 => ALT_ZERO_HASH,
r => r,
}
}
@ -165,7 +176,7 @@ pub fn calc_fn_params_hash(params: impl Iterator<Item = TypeId>) -> u64 {
len.hash(s);
match s.finish() {
0 => DEFAULT_HASH,
0 => ALT_ZERO_HASH,
r => r,
}
}
@ -179,7 +190,7 @@ pub fn calc_fn_params_hash(params: impl Iterator<Item = TypeId>) -> u64 {
#[must_use]
pub const fn combine_hashes(a: u64, b: u64) -> u64 {
match a ^ b {
0 => DEFAULT_HASH,
0 => ALT_ZERO_HASH,
r => r,
}
}

19
src/module/mod.rs
View File

@ -96,8 +96,7 @@ impl FuncInfo {
}
}
/// _(internals)_ Calculate a [`u64`] hash key from a namespace-qualified function name and
/// parameter types.
/// _(internals)_ Calculate a non-zero [`u64`] hash key from a namespace-qualified function name and parameter types.
/// Exported under the `internals` feature only.
///
/// Module names are passed in via `&str` references from an iterator.
@ -667,7 +666,7 @@ impl Module {
type_id
}
/// Set a Rust function into the [`Module`], returning a hash key.
/// Set a Rust function into the [`Module`], returning a non-zero hash key.
///
/// If there is an existing Rust function of the same hash, it is replaced.
///
@ -729,7 +728,7 @@ impl Module {
/// Set a Rust function taking a reference to the scripting [`Engine`][crate::Engine],
/// the current set of functions, plus a list of mutable [`Dynamic`] references
/// into the [`Module`], returning a hash key.
/// into the [`Module`], returning a non-zero hash key.
///
/// Use this to register a built-in function which must reference settings on the scripting
/// [`Engine`][crate::Engine] (e.g. to prevent growing an array beyond the allowed maximum size),
@ -822,7 +821,7 @@ impl Module {
)
}
/// Set a Rust function into the [`Module`], returning a hash key.
/// Set a Rust function into the [`Module`], returning a non-zero hash key.
///
/// If there is a similar existing Rust function, it is replaced.
///
@ -861,7 +860,7 @@ impl Module {
)
}
/// Set a Rust getter function taking one mutable parameter, returning a hash key.
/// Set a Rust getter function taking one mutable parameter, returning a non-zero hash key.
/// This function is automatically exposed to the global namespace.
///
/// If there is a similar existing Rust getter function, it is replaced.
@ -898,7 +897,7 @@ impl Module {
}
/// Set a Rust setter function taking two parameters (the first one mutable) into the [`Module`],
/// returning a hash key.
/// returning a non-zero hash key.
/// This function is automatically exposed to the global namespace.
///
/// If there is a similar existing setter Rust function, it is replaced.
@ -939,7 +938,7 @@ impl Module {
}
/// Set a Rust index getter taking two parameters (the first one mutable) into the [`Module`],
/// returning a hash key.
/// returning a non-zero hash key.
/// This function is automatically exposed to the global namespace.
///
/// If there is a similar existing setter Rust function, it is replaced.
@ -1000,7 +999,7 @@ impl Module {
}
/// Set a Rust index setter taking three parameters (the first one mutable) into the [`Module`],
/// returning a hash key.
/// returning a non-zero hash key.
/// This function is automatically exposed to the global namespace.
///
/// If there is a similar existing Rust function, it is replaced.
@ -1060,7 +1059,7 @@ impl Module {
)
}
/// Set a pair of Rust index getter and setter functions, returning both hash keys.
/// Set a pair of Rust index getter and setter functions, returning both non-zero hash keys.
/// This is a short-hand for [`set_indexer_get_fn`][Module::set_indexer_get_fn] and
/// [`set_indexer_set_fn`][Module::set_indexer_set_fn].
///