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bpo-40602: Add _Py_HashPointerRaw() function (GH-20056) 

Add a new _Py_HashPointerRaw() function which avoids replacing -1
with -2 to micro-optimize hash table using pointer keys: using
_Py_hashtable_hash_ptr() hash function.
This commit is contained in:
Victor Stinner 2020-05-12 18:46:20 +02:00 committed by GitHub
parent 4c9ea093cd
commit f453221c8b
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GPG Key ID: 4AEE18F83AFDEB23
3 changed files with 13 additions and 5 deletions
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2
Include/pyhash.h
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@ -9,6 +9,8 @@ extern "C" {
#ifndef Py_LIMITED_API #ifndef Py_LIMITED_API
PyAPI_FUNC(Py_hash_t) _Py_HashDouble(double); PyAPI_FUNC(Py_hash_t) _Py_HashDouble(double);
PyAPI_FUNC(Py_hash_t) _Py_HashPointer(const void*); PyAPI_FUNC(Py_hash_t) _Py_HashPointer(const void*);
// Similar to _Py_HashPointer(), but don't replace -1 with -2
PyAPI_FUNC(Py_hash_t) _Py_HashPointerRaw(const void*);
PyAPI_FUNC(Py_hash_t) _Py_HashBytes(const void*, Py_ssize_t); PyAPI_FUNC(Py_hash_t) _Py_HashBytes(const void*, Py_ssize_t);
#endif #endif

2
Python/hashtable.c
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@ -109,7 +109,7 @@ _Py_hashtable_hash_ptr(struct _Py_hashtable_t *ht, const void *pkey)
{ {
void *key; void *key;
_Py_HASHTABLE_READ_KEY(ht, pkey, key); _Py_HASHTABLE_READ_KEY(ht, pkey, key);
return (Py_uhash_t)_Py_HashPointer(key); return (Py_uhash_t)_Py_HashPointerRaw(key);
} }

14
Python/pyhash.c
View File

@ -129,16 +129,22 @@ _Py_HashDouble(double v)
} }
Py_hash_t Py_hash_t
_Py_HashPointer(const void *p) _Py_HashPointerRaw(const void *p)
{ {
Py_hash_t x;
size_t y = (size_t)p; size_t y = (size_t)p;
/* bottom 3 or 4 bits are likely to be 0; rotate y by 4 to avoid /* bottom 3 or 4 bits are likely to be 0; rotate y by 4 to avoid
excessive hash collisions for dicts and sets */ excessive hash collisions for dicts and sets */
y = (y >> 4) | (y << (8 * SIZEOF_VOID_P - 4)); y = (y >> 4) | (y << (8 * SIZEOF_VOID_P - 4));
x = (Py_hash_t)y; return (Py_hash_t)y;
if (x == -1) }
Py_hash_t
_Py_HashPointer(const void *p)
{
Py_hash_t x = _Py_HashPointerRaw(p);
if (x == -1) {
x = -2; x = -2;
}
return x; return x;
} }