STINNER Victor <[email protected]> added the comment:
I'm reposting my patch from #12751. I think that it's simpler than belopolsky's
patch: it doesn't add public macros in unicodeobject.h and don't add the
complex Py_UNICODE_NEXT() macro. My patch only adds private macros in
unicodeobject.c to factorize the code.
I don't want to add public macros because with the stable API and with the PEP
393, we are trying to hide the Py_UNICODE type and PyUnicodeObject internals.
In belopolsky's patch, only Py_UNICODE_NEXT() is used outside unicodeobject.c.
Copy/paste of the initial message of my issue #12751 (msg142108):
---------------
A lot of code is duplicated in unicodeobject.c to manipulate ("encode/decode")
surrogates. Each function has from one to three different implementations. The
new decode_ucs4() function adds a new implementation. Attached patch replaces
this code by macros.
I think that only the implementations of IS_HIGH_SURROGATE and IS_LOW_SURROGATE
are important for speed. ((ch & 0xFFFFFC00UL) == 0xD800) (from decode_ucs4) is
*a little bit* faster than (0xD800 <= ch && ch <= 0xDBFF) on my CPU (Atom Z520
@ 1.3 GHz): running test_unicode 4 times takes ~54 sec instead of ~57 sec (-3%).
These 3 macros have to be checked, I wrote the first one:
#define IS_SURROGATE(ch) (((ch) & 0xFFFFF800UL) == 0xD800)
#define IS_HIGH_SURROGATE(ch) (((ch) & 0xFFFFFC00UL) == 0xD800)
#define IS_LOW_SURROGATE(ch) (((ch) & 0xFFFFFC00UL) == 0xDC00)
I added cast to Py_UCS4 in COMBINE_SURROGATES to avoid integer overflow if
Py_UNICODE is 16 bits (narrow build). It's maybe useless.
#define COMBINE_SURROGATES(ch1, ch2) \
(((((Py_UCS4)(ch1) & 0x3FF) << 10) | ((Py_UCS4)(ch2) & 0x3FF)) + 0x10000)
HIGH_SURROGATE and LOW_SURROGATE require that their ordinal argument has been
preproceed to fit in [0; 0xFFFF]. I added this requirement in the comment of
these macros. It would be better to have only one macro to do the two
operations, but because "*p++" (dereference and increment) is usually used, I
prefer to avoid one unique macro (I don't like passing *p++ in a macro using
its argument more than once).
Or we may add a third macro using HIGH_SURROGATE and LOW_SURROGATE.
I rewrote the main loop of PyUnicode_EncodeUTF16() to avoid an useless test on
ch2 on narrow build.
I also added a IS_NONBMP macro just because I prefer macro over hardcoded
constants.
---------------
----------
Added file: http://bugs.python.org/file22915/unicode_macros.patch
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