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QString::{to,from}Latin1: add the ability to do overlapping tails 

If the string length is larger than the number of characters we can
operate on with a single vector loop, we can transform the tail using a
vector too, just overlapping up to 15 characters with the last iteration
o the loop.

Change-Id: Ib42b3adc93bf4d43bd55fffd16c2dcab115e50f7
Reviewed-by: Lars Knoll <lars@knoll.priv.no>
bb10
Thiago Macieira 2021-12-21 16:44:01 -03:00
parent 3b528670e6
commit 2b9d4afc95
1 changed files with 31 additions and 13 deletions
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44
src/corelib/text/qstring.cpp
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@ -803,11 +803,8 @@ Q_CORE_EXPORT void qt_from_latin1(char16_t *dst, const char *str, size_t size) n
* itself in exactly the same way as one would do it with intrinsics.
*/
#if defined(__SSE2__)
const char *e = str + size;
qptrdiff offset = 0;
// we're going to read str[offset..offset+15] (16 bytes)
for ( ; str + offset + 15 < e; offset += 16) {
auto processOneChunk = [=](qptrdiff offset) {
const __m128i chunk = _mm_loadu_si128((const __m128i*)(str + offset)); // load
if constexpr (UseAvx2) {
// zero extend to an YMM register
@ -826,10 +823,21 @@ Q_CORE_EXPORT void qt_from_latin1(char16_t *dst, const char *str, size_t size) n
const __m128i secondHalf = _mm_unpackhi_epi8 (chunk, nullMask);
_mm_storeu_si128((__m128i*)(dst + offset + 8), secondHalf); // store
}
};
const char *e = str + size;
qptrdiff offset = 0;
if (size >= sizeof(__m128i)) {
for ( ; str + offset + sizeof(__m128i) <= e; offset += sizeof(__m128i))
processOneChunk(offset);
if (str + offset < e)
processOneChunk(size - sizeof(__m128i));
return;
}
# if !defined(__OPTIMIZE_SIZE__)
// we're going to read str[offset..offset+7] (8 bytes)
if (str + offset + 7 < e) {
if (str + offset + 8 <= e) {
const __m128i unpacked = mm_load8_zero_extend(str + offset);
_mm_storeu_si128(reinterpret_cast<__m128i *>(dst + offset), unpacked);
offset += 8;
@ -838,7 +846,6 @@ Q_CORE_EXPORT void qt_from_latin1(char16_t *dst, const char *str, size_t size) n
size = size % 8;
dst += offset;
str += offset;
# if !defined(__OPTIMIZE_SIZE__)
return UnrollTailLoop<7>::exec(qsizetype(size), [=](qsizetype i) { dst[i] = (uchar)str[i]; });
# endif
#endif
@ -859,9 +866,6 @@ template <bool Checked>
static void qt_to_latin1_internal(uchar *dst, const char16_t *src, qsizetype length)
{
#if defined(__SSE2__)
uchar *e = dst + length;
qptrdiff offset = 0;
auto questionMark256 = []() {
if constexpr (UseAvx2)
return _mm256_broadcastw_epi16(_mm_cvtsi32_si128('?'));
@ -917,8 +921,8 @@ static void qt_to_latin1_internal(uchar *dst, const char16_t *src, qsizetype len
return chunk;
};
// we're going to write to dst[offset..offset+15] (16 bytes)
for ( ; dst + offset + 15 < e; offset += 16) {
// we're going to read to src[offset..offset+15] (16 bytes)
auto loadChunkAt = [=](qptrdiff offset) {
__m128i chunk1, chunk2;
if constexpr (UseAvx2) {
__m256i chunk = _mm256_loadu_si256(reinterpret_cast<const __m256i *>(src + offset));
@ -940,8 +944,22 @@ static void qt_to_latin1_internal(uchar *dst, const char16_t *src, qsizetype len
}
// pack the two vector to 16 x 8bits elements
const __m128i result = _mm_packus_epi16(chunk1, chunk2);
_mm_storeu_si128((__m128i*)(dst + offset), result); // store
return _mm_packus_epi16(chunk1, chunk2);
};
uchar *e = dst + length;
qptrdiff offset = 0;
if (size_t(length) >= sizeof(__m128i)) {
// because of possible overlapping, we won't process the last chunk in the loop
for ( ; offset + 2 * sizeof(__m128i) < size_t(length); offset += sizeof(__m128i))
_mm_storeu_si128(reinterpret_cast<__m128i *>(dst + offset), loadChunkAt(offset));
// overlapped conversion of the last full chunk and the tail
__m128i last1 = loadChunkAt(offset);
__m128i last2 = loadChunkAt(length - sizeof(__m128i));
_mm_storeu_si128(reinterpret_cast<__m128i *>(dst + offset), last1);
_mm_storeu_si128(reinterpret_cast<__m128i *>(dst + length - sizeof(__m128i)), last2);
return;
}
# if !defined(__OPTIMIZE_SIZE__)