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Two speedup hacks. Caching the hash saves recalculation of a string's 

hash value.  Interning strings (which requires hash caching) tries to
ensure that only one string object with a given value exists, so
equality tests are one pointer comparison.  Together, these can speed
the interpreter up by as much as 20%.  Each costs the size of a long
or pointer per string object.  In addition, interned strings live
until the end of times.  If you are concerned about memory footprint,
simply comment the #define out here (and rebuild everything!).
This commit is contained in:
Guido van Rossum 1997-01-18 07:53:23 +00:00
parent 3dfd53b4c8
commit 1e6e9a2368
1 changed files with 23 additions and 3 deletions
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26
Include/stringobject.h
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@ -52,15 +52,27 @@ variant that assumes a zero-terminated string. Note that none of the
functions should be applied to nil objects.
*/
/* NB The type is revealed here only because it is used in dictobject.c */
/* Take this out to save 4 bytes per string object and to lose 2% speedup */
/* Two speedup hacks. Caching the hash saves recalculation of a
string's hash value. Interning strings (which requires hash
caching) tries to ensure that only one string object with a given
value exists, so equality tests are one pointer comparison.
Together, these can speed the interpreter up by as much as 20%.
Each costs the size of a long or pointer per string object. In
addition, interned strings live until the end of times. If you are
concerned about memory footprint, simply comment the #define out
here (and rebuild everything!). */
#define CACHE_HASH
#ifdef CACHE_HASH
#define INTERN_STRINGS
#endif
typedef struct {
PyObject_VAR_HEAD
#ifdef CACHE_HASH
long ob_shash;
#endif
#ifdef INTERN_STRINGS
PyObject *ob_sinterned;
#endif
char ob_sval[1];
} PyStringObject;
@ -78,6 +90,14 @@ extern void PyString_ConcatAndDel Py_PROTO((PyObject **, PyObject *));
extern int _PyString_Resize Py_PROTO((PyObject **, int));
extern PyObject *PyString_Format Py_PROTO((PyObject *, PyObject *));
#ifdef INTERN_STRINGS
extern void PyString_InternInPlace Py_PROTO((PyObject **));
extern PyObject *PyString_InternFromString Py_PROTO((const char *));
#else
#define PyString_InternInPlace(p)
#define PyString_InternFromString(cp) PyString_FromString(cp)
#endif
/* Macro, trading safety for speed */
#define PyString_AS_STRING(op) (((PyStringObject *)(op))->ob_sval)
#define PyString_GET_SIZE(op) (((PyStringObject *)(op))->ob_size)