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bpo-38252: use 8-byte step to detect ASCII sequence in 64bit Windows build #16334

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Merged
merged 6 commits into from Oct 18, 2020
Merged

bpo-38252: use 8-byte step to detect ASCII sequence in 64bit Windows build #16334

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645f01e
ucs1lib_find_max_char
wjssz Sep 23, 2019
c50ed3b
ascii_decode
wjssz Sep 23, 2019
56866ab
utf8_decode
wjssz Sep 23, 2019
fff1754
_Py_bytes_isascii
wjssz Sep 23, 2019
f7833b4
Merge branch 'master' into win_max_char
animalize Jun 12, 2020
b00a527
add news entry
wjssz Oct 18, 2020
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Windows/2020-10-18-18-43-45.bpo-38252.7Nlepg.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Use 8-byte step to detect ASCII sequence in 64-bit Windows build.
20 changes: 10 additions & 10 deletions Objects/bytes_methods.c
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Expand Up @@ -100,35 +100,35 @@ Return True if B is empty or all characters in B are ASCII,\n\
False otherwise.");

// Optimization is copied from ascii_decode in unicodeobject.c
/* Mask to quickly check whether a C 'long' contains a
/* Mask to quickly check whether a C 'size_t' contains a
non-ASCII, UTF8-encoded char. */
#if (SIZEOF_LONG == 8)
# define ASCII_CHAR_MASK 0x8080808080808080UL
#elif (SIZEOF_LONG == 4)
# define ASCII_CHAR_MASK 0x80808080UL
#if (SIZEOF_SIZE_T == 8)
# define ASCII_CHAR_MASK 0x8080808080808080ULL
#elif (SIZEOF_SIZE_T == 4)
# define ASCII_CHAR_MASK 0x80808080U
#else
# error C 'long' size should be either 4 or 8!
# error C 'size_t' size should be either 4 or 8!
#endif

PyObject*
_Py_bytes_isascii(const char *cptr, Py_ssize_t len)
{
const char *p = cptr;
const char *end = p + len;
const char *aligned_end = (const char *) _Py_ALIGN_DOWN(end, SIZEOF_LONG);
const char *aligned_end = (const char *) _Py_ALIGN_DOWN(end, SIZEOF_SIZE_T);

while (p < end) {
/* Fast path, see in STRINGLIB(utf8_decode) in stringlib/codecs.h
for an explanation. */
if (_Py_IS_ALIGNED(p, SIZEOF_LONG)) {
if (_Py_IS_ALIGNED(p, SIZEOF_SIZE_T)) {
/* Help allocation */
const char *_p = p;
while (_p < aligned_end) {
unsigned long value = *(const unsigned long *) _p;
size_t value = *(const size_t *) _p;
if (value & ASCII_CHAR_MASK) {
Py_RETURN_FALSE;
}
_p += SIZEOF_LONG;
_p += SIZEOF_SIZE_T;
}
p = _p;
if (_p == end)
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30 changes: 15 additions & 15 deletions Objects/stringlib/codecs.h
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Expand Up @@ -6,14 +6,14 @@

#include "pycore_bitutils.h" // _Py_bswap32()

/* Mask to quickly check whether a C 'long' contains a
/* Mask to quickly check whether a C 'size_t' contains a
non-ASCII, UTF8-encoded char. */
#if (SIZEOF_LONG == 8)
# define ASCII_CHAR_MASK 0x8080808080808080UL
#elif (SIZEOF_LONG == 4)
# define ASCII_CHAR_MASK 0x80808080UL
#if (SIZEOF_SIZE_T == 8)
# define ASCII_CHAR_MASK 0x8080808080808080ULL
#elif (SIZEOF_SIZE_T == 4)
# define ASCII_CHAR_MASK 0x80808080U
#else
# error C 'long' size should be either 4 or 8!
# error C 'size_t' size should be either 4 or 8!
#endif

/* 10xxxxxx */
Expand All @@ -26,7 +26,7 @@ STRINGLIB(utf8_decode)(const char **inptr, const char *end,
{
Py_UCS4 ch;
const char *s = *inptr;
const char *aligned_end = (const char *) _Py_ALIGN_DOWN(end, SIZEOF_LONG);
const char *aligned_end = (const char *) _Py_ALIGN_DOWN(end, SIZEOF_SIZE_T);
STRINGLIB_CHAR *p = dest + *outpos;

while (s < end) {
Expand All @@ -36,34 +36,34 @@ STRINGLIB(utf8_decode)(const char **inptr, const char *end,
/* Fast path for runs of ASCII characters. Given that common UTF-8
input will consist of an overwhelming majority of ASCII
characters, we try to optimize for this case by checking
as many characters as a C 'long' can contain.
as many characters as a C 'size_t' can contain.
First, check if we can do an aligned read, as most CPUs have
a penalty for unaligned reads.
*/
if (_Py_IS_ALIGNED(s, SIZEOF_LONG)) {
if (_Py_IS_ALIGNED(s, SIZEOF_SIZE_T)) {
/* Help register allocation */
const char *_s = s;
STRINGLIB_CHAR *_p = p;
while (_s < aligned_end) {
/* Read a whole long at a time (either 4 or 8 bytes),
/* Read a whole size_t at a time (either 4 or 8 bytes),
and do a fast unrolled copy if it only contains ASCII
characters. */
unsigned long value = *(const unsigned long *) _s;
size_t value = *(const size_t *) _s;
if (value & ASCII_CHAR_MASK)
break;
#if PY_LITTLE_ENDIAN
_p[0] = (STRINGLIB_CHAR)(value & 0xFFu);
_p[1] = (STRINGLIB_CHAR)((value >> 8) & 0xFFu);
_p[2] = (STRINGLIB_CHAR)((value >> 16) & 0xFFu);
_p[3] = (STRINGLIB_CHAR)((value >> 24) & 0xFFu);
# if SIZEOF_LONG == 8
# if SIZEOF_SIZE_T == 8
_p[4] = (STRINGLIB_CHAR)((value >> 32) & 0xFFu);
_p[5] = (STRINGLIB_CHAR)((value >> 40) & 0xFFu);
_p[6] = (STRINGLIB_CHAR)((value >> 48) & 0xFFu);
_p[7] = (STRINGLIB_CHAR)((value >> 56) & 0xFFu);
# endif
#else
# if SIZEOF_LONG == 8
# if SIZEOF_SIZE_T == 8
_p[0] = (STRINGLIB_CHAR)((value >> 56) & 0xFFu);
_p[1] = (STRINGLIB_CHAR)((value >> 48) & 0xFFu);
_p[2] = (STRINGLIB_CHAR)((value >> 40) & 0xFFu);
Expand All @@ -79,8 +79,8 @@ STRINGLIB(utf8_decode)(const char **inptr, const char *end,
_p[3] = (STRINGLIB_CHAR)(value & 0xFFu);
# endif
#endif
_s += SIZEOF_LONG;
_p += SIZEOF_LONG;
_s += SIZEOF_SIZE_T;
_p += SIZEOF_SIZE_T;
}
s = _s;
p = _p;
Expand Down
20 changes: 10 additions & 10 deletions Objects/stringlib/find_max_char.h
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Expand Up @@ -4,14 +4,14 @@
# error "find_max_char.h is specific to Unicode"
#endif

/* Mask to quickly check whether a C 'long' contains a
/* Mask to quickly check whether a C 'size_t' contains a
non-ASCII, UTF8-encoded char. */
#if (SIZEOF_LONG == 8)
# define UCS1_ASCII_CHAR_MASK 0x8080808080808080UL
#elif (SIZEOF_LONG == 4)
# define UCS1_ASCII_CHAR_MASK 0x80808080UL
#if (SIZEOF_SIZE_T == 8)
# define UCS1_ASCII_CHAR_MASK 0x8080808080808080ULL
#elif (SIZEOF_SIZE_T == 4)
# define UCS1_ASCII_CHAR_MASK 0x80808080U
#else
# error C 'long' size should be either 4 or 8!
# error C 'size_t' size should be either 4 or 8!
#endif

#if STRINGLIB_SIZEOF_CHAR == 1
Expand All @@ -21,17 +21,17 @@ STRINGLIB(find_max_char)(const STRINGLIB_CHAR *begin, const STRINGLIB_CHAR *end)
{
const unsigned char *p = (const unsigned char *) begin;
const unsigned char *aligned_end =
(const unsigned char *) _Py_ALIGN_DOWN(end, SIZEOF_LONG);
(const unsigned char *) _Py_ALIGN_DOWN(end, SIZEOF_SIZE_T);

while (p < end) {
if (_Py_IS_ALIGNED(p, SIZEOF_LONG)) {
if (_Py_IS_ALIGNED(p, SIZEOF_SIZE_T)) {
/* Help register allocation */
const unsigned char *_p = p;
while (_p < aligned_end) {
unsigned long value = *(const unsigned long *) _p;
size_t value = *(const size_t *) _p;
if (value & UCS1_ASCII_CHAR_MASK)
return 255;
_p += SIZEOF_LONG;
_p += SIZEOF_SIZE_T;
}
p = _p;
if (p == end)
Expand Down
34 changes: 17 additions & 17 deletions Objects/unicodeobject.c
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Expand Up @@ -4896,21 +4896,21 @@ PyUnicode_DecodeUTF8(const char *s,
#include "stringlib/codecs.h"
#include "stringlib/undef.h"

/* Mask to quickly check whether a C 'long' contains a
/* Mask to quickly check whether a C 'size_t' contains a
non-ASCII, UTF8-encoded char. */
#if (SIZEOF_LONG == 8)
# define ASCII_CHAR_MASK 0x8080808080808080UL
#elif (SIZEOF_LONG == 4)
# define ASCII_CHAR_MASK 0x80808080UL
#if (SIZEOF_SIZE_T == 8)
# define ASCII_CHAR_MASK 0x8080808080808080ULL
#elif (SIZEOF_SIZE_T == 4)
# define ASCII_CHAR_MASK 0x80808080U
#else
# error C 'long' size should be either 4 or 8!
# error C 'size_t' size should be either 4 or 8!
#endif

static Py_ssize_t
ascii_decode(const char *start, const char *end, Py_UCS1 *dest)
{
const char *p = start;
const char *aligned_end = (const char *) _Py_ALIGN_DOWN(end, SIZEOF_LONG);
const char *aligned_end = (const char *) _Py_ALIGN_DOWN(end, SIZEOF_SIZE_T);

/*
* Issue #17237: m68k is a bit different from most architectures in
Expand All @@ -4920,21 +4920,21 @@ ascii_decode(const char *start, const char *end, Py_UCS1 *dest)
* version" will even speed up m68k.
*/
#if !defined(__m68k__)
#if SIZEOF_LONG <= SIZEOF_VOID_P
assert(_Py_IS_ALIGNED(dest, SIZEOF_LONG));
if (_Py_IS_ALIGNED(p, SIZEOF_LONG)) {
#if SIZEOF_SIZE_T <= SIZEOF_VOID_P
assert(_Py_IS_ALIGNED(dest, SIZEOF_SIZE_T));
if (_Py_IS_ALIGNED(p, SIZEOF_SIZE_T)) {
/* Fast path, see in STRINGLIB(utf8_decode) for
an explanation. */
/* Help allocation */
const char *_p = p;
Py_UCS1 * q = dest;
while (_p < aligned_end) {
unsigned long value = *(const unsigned long *) _p;
size_t value = *(const size_t *) _p;
if (value & ASCII_CHAR_MASK)
break;
*((unsigned long *)q) = value;
_p += SIZEOF_LONG;
q += SIZEOF_LONG;
*((size_t *)q) = value;
_p += SIZEOF_SIZE_T;
q += SIZEOF_SIZE_T;
}
p = _p;
while (p < end) {
Expand All @@ -4949,14 +4949,14 @@ ascii_decode(const char *start, const char *end, Py_UCS1 *dest)
while (p < end) {
/* Fast path, see in STRINGLIB(utf8_decode) in stringlib/codecs.h
for an explanation. */
if (_Py_IS_ALIGNED(p, SIZEOF_LONG)) {
if (_Py_IS_ALIGNED(p, SIZEOF_SIZE_T)) {
/* Help allocation */
const char *_p = p;
while (_p < aligned_end) {
unsigned long value = *(const unsigned long *) _p;
size_t value = *(const size_t *) _p;
if (value & ASCII_CHAR_MASK)
break;
_p += SIZEOF_LONG;
_p += SIZEOF_SIZE_T;
}
p = _p;
if (_p == end)
Expand Down