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Improve the QString/QLatin1String ucstrncmp with SSE2

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Change-Id: I6a7ce281096bb99352132f775ae32fcaf55bd32c
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
This commit is contained in:
Thiago Macieira 2013-12-13 13:21:09 -08:00 committed by The Qt Project
parent 3bae7b0a28
commit 4c9db39896
1 changed files with 51 additions and 0 deletions
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51
src/corelib/tools/qstring.cpp
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@ -312,6 +312,57 @@ static int ucstrncmp(const QChar *a, const uchar *c, int l)
const ushort *uc = reinterpret_cast<const ushort *>(a);
const ushort *e = uc + l;
#ifdef __SSE2__
__m128i nullmask = _mm_setzero_si128();
qptrdiff offset = 0;
// we're going to read uc[offset..offset+15] (32 bytes)
// and c[offset..offset+15] (16 bytes)
for ( ; uc + offset + 15 < e; offset += 16) {
// similar to fromLatin1_helper:
// load Latin 1 data and expand to UTF-16
__m128i chunk = _mm_loadu_si128((__m128i*)(c + offset));
__m128i firstHalf = _mm_unpacklo_epi8(chunk, nullmask);
__m128i secondHalf = _mm_unpackhi_epi8(chunk, nullmask);
// load UTF-16 data and compare
__m128i ucdata1 = _mm_loadu_si128((__m128i*)(uc + offset));
__m128i ucdata2 = _mm_loadu_si128((__m128i*)(uc + offset + 8));
__m128i result1 = _mm_cmpeq_epi16(firstHalf, ucdata1);
__m128i result2 = _mm_cmpeq_epi16(secondHalf, ucdata2);
uint mask = ~(_mm_movemask_epi8(result1) | _mm_movemask_epi8(result2) << 16);
if (mask) {
// found a different character
uint idx = uint(_bit_scan_forward(mask));
return uc[offset + idx / 2] - c[offset + idx / 2];
}
}
// we'll read uc[offset..offset+7] (16 bytes) and c[offset-8..offset+7] (16 bytes)
if (uc + offset + 7 < e) {
// same, but we'll throw away half the data
__m128i chunk = _mm_loadu_si128((__m128i*)(c + offset - 8));
__m128i secondHalf = _mm_unpackhi_epi8(chunk, nullmask);
__m128i ucdata = _mm_loadu_si128((__m128i*)(uc + offset));
__m128i result = _mm_cmpeq_epi16(secondHalf, ucdata);
uint mask = ~_mm_movemask_epi8(result);
if (ushort(mask)) {
// found a different character
uint idx = uint(_bit_scan_forward(mask));
return uc[offset + idx / 2] - c[offset + idx / 2];
}
// still matched
offset += 8;
}
// reset uc and c
uc += offset;
c += offset;
#endif
while (uc < e) {
int diff = *uc - *c;
if (diff)