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hashlib: declare YS_HASHING_VERSION = 1

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This commit is contained in:
Emil J. Tywoniak 2024-11-19 20:01:41 +01:00
parent 1df8a3e64b
commit 0a525f38c2
2 changed files with 16 additions and 12 deletions
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26
docs/source/yosys_internals/hashing.rst
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@ -131,23 +131,25 @@ Previously, the interface to implement hashing on custom types was just
``unsigned int T::hash() const``. This meant hashes for members were computed
independently and then ad-hoc combined with the hash function with some xorshift
operations thrown in to mix bits together somewhat. A plugin can stay compatible
with both versions prior and after the break by implementing the aforementioned
current interface and redirecting the legacy one:
``void Hasher::eat(const T& t)`` hashes ``t`` into its internal state by also
redirecting to ``hash_ops<T>``
with both versions prior and after the break by implementing both interfaces
based on the existance and value of `YS_HASHING_VERSION`.
.. code-block:: cpp
:caption: Example hash compatibility wrapper
:name: hash_plugin_compat
inline unsigned int T::hash() const {
Hasher h;
return (unsigned int)hash_eat(h).yield();
#ifndef YS_HASHING_VERSION
unsigned int T::hash() const {
return mkhash(a, b);
}
#elif YS_HASHING_VERSION == 1
Hasher T::hash_eat(Hasher h) const {
h.eat(a);
h.eat(b);
return h;
}
#else
#error "Unsupported hashing interface"
#endif
To get hashes for Yosys types, you can temporarily use the templated deprecated
``mkhash`` function until the majority of your plugin's users switch to a newer
version and live with the warnings, or set up a custom ``#ifdef``-based solution
if you really need to.
Feel free to contact Yosys maintainers with related issues.