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annotate Include/stringobject.h @ 5003:65aace2012e5 legacy-trunk

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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!).
author Guido van Rossum <guido@python.org>
date Sat, 18 Jan 1997 07:53:23 +0000
parents 90c21dde4284
children 60fdb1db1175
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1 #ifndef Py_STRINGOBJECT_H
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2 #define Py_STRINGOBJECT_H
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3 #ifdef __cplusplus
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4 extern "C" {
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5 #endif
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6
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7 /***********************************************************
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8 Copyright 1991-1995 by Stichting Mathematisch Centrum, Amsterdam,
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9 The Netherlands.
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10
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11 All Rights Reserved
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12
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13 Permission to use, copy, modify, and distribute this software and its
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14 documentation for any purpose and without fee is hereby granted,
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15 provided that the above copyright notice appear in all copies and that
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16 both that copyright notice and this permission notice appear in
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17 supporting documentation, and that the names of Stichting Mathematisch
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18 Centrum or CWI or Corporation for National Research Initiatives or
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19 CNRI not be used in advertising or publicity pertaining to
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20 distribution of the software without specific, written prior
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21 permission.
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22
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23 While CWI is the initial source for this software, a modified version
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24 is made available by the Corporation for National Research Initiatives
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25 (CNRI) at the Internet address ftp://ftp.python.org.
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26
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27 STICHTING MATHEMATISCH CENTRUM AND CNRI DISCLAIM ALL WARRANTIES WITH
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28 REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF
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29 MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH
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30 CENTRUM OR CNRI BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL
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31 DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
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32 PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
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33 TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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34 PERFORMANCE OF THIS SOFTWARE.
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35
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36 ******************************************************************/
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37
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38 /* String object interface */
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39
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40 /*
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41 Type PyStringObject represents a character string. An extra zero byte is
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42 reserved at the end to ensure it is zero-terminated, but a size is
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43 present so strings with null bytes in them can be represented. This
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44 is an immutable object type.
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45
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46 There are functions to create new string objects, to test
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47 an object for string-ness, and to get the
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48 string value. The latter function returns a null pointer
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49 if the object is not of the proper type.
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50 There is a variant that takes an explicit size as well as a
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51 variant that assumes a zero-terminated string. Note that none of the
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52 functions should be applied to nil objects.
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53 */
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54
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55 /* Two speedup hacks. Caching the hash saves recalculation of a
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56 string's hash value. Interning strings (which requires hash
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57 caching) tries to ensure that only one string object with a given
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58 value exists, so equality tests are one pointer comparison.
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59 Together, these can speed the interpreter up by as much as 20%.
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60 Each costs the size of a long or pointer per string object. In
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61 addition, interned strings live until the end of times. If you are
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62 concerned about memory footprint, simply comment the #define out
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63 here (and rebuild everything!). */
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64 #define CACHE_HASH
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65 #ifdef CACHE_HASH
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66 #define INTERN_STRINGS
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67 #endif
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68
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69 typedef struct {
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70 PyObject_VAR_HEAD
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71 #ifdef CACHE_HASH
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72 long ob_shash;
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73 #endif
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74 #ifdef INTERN_STRINGS
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75 PyObject *ob_sinterned;
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76 #endif
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77 char ob_sval[1];
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78 } PyStringObject;
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79
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80 extern DL_IMPORT(PyTypeObject) PyString_Type;
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81
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82 #define PyString_Check(op) ((op)->ob_type == &PyString_Type)
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83
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84 extern PyObject *PyString_FromStringAndSize Py_PROTO((const char *, int));
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85 extern PyObject *PyString_FromString Py_PROTO((const char *));
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86 extern int PyString_Size Py_PROTO((PyObject *));
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87 extern char *PyString_AsString Py_PROTO((PyObject *));
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88 extern void PyString_Concat Py_PROTO((PyObject **, PyObject *));
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89 extern void PyString_ConcatAndDel Py_PROTO((PyObject **, PyObject *));
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90 extern int _PyString_Resize Py_PROTO((PyObject **, int));
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91 extern PyObject *PyString_Format Py_PROTO((PyObject *, PyObject *));
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92
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93 #ifdef INTERN_STRINGS
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94 extern void PyString_InternInPlace Py_PROTO((PyObject **));
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95 extern PyObject *PyString_InternFromString Py_PROTO((const char *));
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96 #else
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97 #define PyString_InternInPlace(p)
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98 #define PyString_InternFromString(cp) PyString_FromString(cp)
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99 #endif
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100
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101 /* Macro, trading safety for speed */
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102 #define PyString_AS_STRING(op) (((PyStringObject *)(op))->ob_sval)
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103 #define PyString_GET_SIZE(op) (((PyStringObject *)(op))->ob_size)
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104
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105 #ifdef __cplusplus
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106 }
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107 #endif
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108 #endif /* !Py_STRINGOBJECT_H */