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Merge pull request #87 from miloyip/issue85simdsegfault

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Fix SIMD page fault by using aligned load
This commit is contained in:
Milo Yip
2014-07-29 16:39:13 +08:00
parent fdd380bbc0 a32e2ac1d0
commit c4f64e7b02
1 changed files with 82 additions and 24 deletions
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106
include/rapidjson/reader.h
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@@ -178,21 +178,56 @@ void SkipWhitespace(InputStream& is) {
//! Skip whitespace with SSE 4.2 pcmpistrm instruction, testing 16 8-byte characters at once. //! Skip whitespace with SSE 4.2 pcmpistrm instruction, testing 16 8-byte characters at once.
inline const char *SkipWhitespace_SIMD(const char* p) { inline const char *SkipWhitespace_SIMD(const char* p) {
static const char whitespace[16] = " \n\r\t"; static const char whitespace[16] = " \n\r\t";
__m128i w = _mm_loadu_si128((const __m128i *)&whitespace[0]); static const char whitespaces[4][17] = {
" ",
"\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n",
"\r\r\r\r\r\r\r\r\r\r\r\r\r\r\r\r",
"\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t"};
for (;;) { // 16-byte align to the lower boundary
__m128i s = _mm_loadu_si128((const __m128i *)p); const char* ap = reinterpret_cast<const char*>(reinterpret_cast<size_t>(p) & ~15);
unsigned r = _mm_cvtsi128_si32(_mm_cmpistrm(w, s, _SIDD_UBYTE_OPS | _SIDD_CMP_EQUAL_ANY | _SIDD_BIT_MASK | _SIDD_NEGATIVE_POLARITY));
if (r == 0) // all 16 characters are whitespace // Test first unaligned characters
p += 16; // Cannot make use of _mm_cmpistrm() because it stops when encounters '\0' before p
else { // some of characters may be non-whitespace if (ap != p) {
const __m128i w0 = _mm_loadu_si128((const __m128i *)&whitespaces[0][0]);
const __m128i w1 = _mm_loadu_si128((const __m128i *)&whitespaces[1][0]);
const __m128i w2 = _mm_loadu_si128((const __m128i *)&whitespaces[2][0]);
const __m128i w3 = _mm_loadu_si128((const __m128i *)&whitespaces[3][0]);
unsigned char shift = reinterpret_cast<size_t>(p) & 15;
const __m128i s = _mm_load_si128(reinterpret_cast<const __m128i*>(ap));
__m128i x = _mm_cmpeq_epi8(s, w0);
x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w1));
x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w2));
x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w3));
unsigned short r = (unsigned short)~_mm_movemask_epi8(x);
r = r >> shift << shift; // Clear results before p
if (r != 0) {
#ifdef _MSC_VER // Find the index of first non-whitespace #ifdef _MSC_VER // Find the index of first non-whitespace
unsigned long offset; unsigned long offset;
if (_BitScanForward(&offset, r)) _BitScanForward(&offset, r);
return p + offset; return ap + offset;
#else #else
if (r != 0) return ap + __builtin_ffs(r) - 1;
return p + __builtin_ffs(r) - 1; #endif
}
ap += 16;
}
const __m128i w = _mm_loadu_si128((const __m128i *)&whitespace[0]);
// The rest of string
for (;; ap += 16) {
const __m128i s = _mm_load_si128((const __m128i *)ap);
const unsigned r = _mm_cvtsi128_si32(_mm_cmpistrm(w, s, _SIDD_UBYTE_OPS | _SIDD_CMP_EQUAL_ANY | _SIDD_BIT_MASK | _SIDD_NEGATIVE_POLARITY));
if (r != 0) { // some of characters is non-whitespace
#ifdef _MSC_VER // Find the index of first non-whitespace
unsigned long offset;
_BitScanForward(&offset, r);
return ap + offset;
#else
return ap + __builtin_ffs(r) - 1;
#endif #endif
} }
} }
@@ -208,28 +243,51 @@ inline const char *SkipWhitespace_SIMD(const char* p) {
"\r\r\r\r\r\r\r\r\r\r\r\r\r\r\r\r", "\r\r\r\r\r\r\r\r\r\r\r\r\r\r\r\r",
"\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t"}; "\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t"};
__m128i w0 = _mm_loadu_si128((const __m128i *)&whitespaces[0][0]); const __m128i w0 = _mm_loadu_si128((const __m128i *)&whitespaces[0][0]);
__m128i w1 = _mm_loadu_si128((const __m128i *)&whitespaces[1][0]); const __m128i w1 = _mm_loadu_si128((const __m128i *)&whitespaces[1][0]);
__m128i w2 = _mm_loadu_si128((const __m128i *)&whitespaces[2][0]); const __m128i w2 = _mm_loadu_si128((const __m128i *)&whitespaces[2][0]);
__m128i w3 = _mm_loadu_si128((const __m128i *)&whitespaces[3][0]); const __m128i w3 = _mm_loadu_si128((const __m128i *)&whitespaces[3][0]);
for (;;) { // 16-byte align to the lower boundary
__m128i s = _mm_loadu_si128((const __m128i *)p); const char* ap = reinterpret_cast<const char*>(reinterpret_cast<size_t>(p) & ~15);
// Test first unaligned characters
if (ap != p) {
unsigned char shift = reinterpret_cast<size_t>(p) & 15;
const __m128i s = _mm_load_si128(reinterpret_cast<const __m128i*>(ap));
__m128i x = _mm_cmpeq_epi8(s, w0); __m128i x = _mm_cmpeq_epi8(s, w0);
x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w1)); x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w1));
x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w2)); x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w2));
x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w3)); x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w3));
unsigned short r = (unsigned short)~_mm_movemask_epi8(x); unsigned short r = (unsigned short)~_mm_movemask_epi8(x);
if (r == 0) // all 16 characters are whitespace r = r >> shift << shift; // Clear results before p
p += 16; if (r != 0) {
else { // some of characters may be non-whitespace
#ifdef _MSC_VER // Find the index of first non-whitespace #ifdef _MSC_VER // Find the index of first non-whitespace
unsigned long offset; unsigned long offset;
if (_BitScanForward(&offset, r)) _BitScanForward(&offset, r);
return p + offset; return ap + offset;
#else #else
if (r != 0) return ap + __builtin_ffs(r) - 1;
return p + __builtin_ffs(r) - 1; #endif
}
ap += 16;
}
// The rest of string
for (;; ap += 16) {
const __m128i s = _mm_load_si128((const __m128i *)ap);
__m128i x = _mm_cmpeq_epi8(s, w0);
x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w1));
x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w2));
x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w3));
unsigned short r = (unsigned short)~_mm_movemask_epi8(x);
if (r != 0) { // some of characters may be non-whitespace
#ifdef _MSC_VER // Find the index of first non-whitespace
unsigned long offset;
_BitScanForward(&offset, r);
return ap + offset;
#else
return ap + __builtin_ffs(r) - 1;
#endif #endif
} }
} }