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Issue #14624: UTF-16 decoding is now 3x to 4x faster on various inputs.

Browse source 
Patch by Serhiy Storchaka.
This commit is contained in:
Antoine Pitrou 2012-05-15 23:48:04 +02:00
parent 12ea86adce
commit 63065d761e
3 changed files with 230 additions and 199 deletions
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149
Objects/stringlib/codecs.h
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@ -215,7 +215,6 @@ InvalidContinuation:
goto Return;
}
#undef LONG_PTR_MASK
#undef ASCII_CHAR_MASK
@ -415,4 +414,152 @@ STRINGLIB(utf8_encoder)(PyObject *unicode,
#undef MAX_SHORT_UNICHARS
}
/* The pattern for constructing UCS2-repeated masks. */
#if SIZEOF_LONG == 8
# define UCS2_REPEAT_MASK 0x0001000100010001ul
#elif SIZEOF_LONG == 4
# define UCS2_REPEAT_MASK 0x00010001ul
#else
# error C 'long' size should be either 4 or 8!
#endif
/* The mask for fast checking. */
#if STRINGLIB_SIZEOF_CHAR == 1
/* The mask for fast checking of whether a C 'long' contains a
non-ASCII or non-Latin1 UTF16-encoded characters. */
# define FAST_CHAR_MASK (UCS2_REPEAT_MASK * (0xFFFFu & ~STRINGLIB_MAX_CHAR))
#else
/* The mask for fast checking of whether a C 'long' may contain
UTF16-encoded surrogate characters. This is an efficient heuristic,
assuming that non-surrogate characters with a code point >= 0x8000 are
rare in most input.
*/
# define FAST_CHAR_MASK (UCS2_REPEAT_MASK * 0x8000u)
#endif
/* The mask for fast byte-swapping. */
#define STRIPPED_MASK (UCS2_REPEAT_MASK * 0x00FFu)
/* Swap bytes. */
#define SWAB(value) ((((value) >> 8) & STRIPPED_MASK) | \
(((value) & STRIPPED_MASK) << 8))
Py_LOCAL_INLINE(Py_UCS4)
STRINGLIB(utf16_decode)(const unsigned char **inptr, const unsigned char *e,
STRINGLIB_CHAR *dest, Py_ssize_t *outpos,
int native_ordering)
{
Py_UCS4 ch;
const unsigned char *aligned_end =
(const unsigned char *) ((size_t) e & ~LONG_PTR_MASK);
const unsigned char *q = *inptr;
STRINGLIB_CHAR *p = dest + *outpos;
/* Offsets from q for retrieving byte pairs in the right order. */
#ifdef BYTEORDER_IS_LITTLE_ENDIAN
int ihi = !!native_ordering, ilo = !native_ordering;
#else
int ihi = !native_ordering, ilo = !!native_ordering;
#endif
--e;
while (q < e) {
Py_UCS4 ch2;
/* First check for possible aligned read of a C 'long'. Unaligned
reads are more expensive, better to defer to another iteration. */
if (!((size_t) q & LONG_PTR_MASK)) {
/* Fast path for runs of in-range non-surrogate chars. */
register const unsigned char *_q = q;
while (_q < aligned_end) {
unsigned long block = * (unsigned long *) _q;
if (native_ordering) {
/* Can use buffer directly */
if (block & FAST_CHAR_MASK)
break;
}
else {
/* Need to byte-swap */
if (block & SWAB(FAST_CHAR_MASK))
break;
#if STRINGLIB_SIZEOF_CHAR == 1
block >>= 8;
#else
block = SWAB(block);
#endif
}
#ifdef BYTEORDER_IS_LITTLE_ENDIAN
# if SIZEOF_LONG == 4
p[0] = (STRINGLIB_CHAR)(block & 0xFFFFu);
p[1] = (STRINGLIB_CHAR)(block >> 16);
# elif SIZEOF_LONG == 8
p[0] = (STRINGLIB_CHAR)(block & 0xFFFFu);
p[1] = (STRINGLIB_CHAR)((block >> 16) & 0xFFFFu);
p[2] = (STRINGLIB_CHAR)((block >> 32) & 0xFFFFu);
p[3] = (STRINGLIB_CHAR)(block >> 48);
# endif
#else
# if SIZEOF_LONG == 4
p[0] = (STRINGLIB_CHAR)(block >> 16);
p[1] = (STRINGLIB_CHAR)(block & 0xFFFFu);
# elif SIZEOF_LONG == 8
p[0] = (STRINGLIB_CHAR)(block >> 48);
p[1] = (STRINGLIB_CHAR)((block >> 32) & 0xFFFFu);
p[2] = (STRINGLIB_CHAR)((block >> 16) & 0xFFFFu);
p[3] = (STRINGLIB_CHAR)(block & 0xFFFFu);
# endif
#endif
_q += SIZEOF_LONG;
p += SIZEOF_LONG / 2;
}
q = _q;
if (q >= e)
break;
}
ch = (q[ihi] << 8) | q[ilo];
q += 2;
if (!Py_UNICODE_IS_SURROGATE(ch)) {
#if STRINGLIB_SIZEOF_CHAR < 2
if (ch > STRINGLIB_MAX_CHAR)
/* Out-of-range */
goto Return;
#endif
*p++ = (STRINGLIB_CHAR)ch;
continue;
}
/* UTF-16 code pair: */
if (q >= e)
goto UnexpectedEnd;
if (!Py_UNICODE_IS_HIGH_SURROGATE(ch))
goto IllegalEncoding;
ch2 = (q[ihi] << 8) | q[ilo];
q += 2;
if (!Py_UNICODE_IS_LOW_SURROGATE(ch2))
goto IllegalSurrogate;
ch = Py_UNICODE_JOIN_SURROGATES(ch, ch2);
#if STRINGLIB_SIZEOF_CHAR < 4
/* Out-of-range */
goto Return;
#else
*p++ = (STRINGLIB_CHAR)ch;
#endif
}
ch = 0;
Return:
*inptr = q;
*outpos = p - dest;
return ch;
UnexpectedEnd:
ch = 1;
goto Return;
IllegalEncoding:
ch = 2;
goto Return;
IllegalSurrogate:
ch = 3;
goto Return;
}
#undef UCS2_REPEAT_MASK
#undef FAST_CHAR_MASK
#undef STRIPPED_MASK
#undef SWAB
#undef LONG_PTR_MASK
#endif /* STRINGLIB_IS_UNICODE */