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Replace memchr with manual memory search

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On large files with predominantly \n line endings, memchr(..'\r'..)
seems to waste a considerable amount of time searching for a line
ending candidate that we don't need.

On the Adobe PDF Reference Manual 1.7, this commit is 8x faster at
QPDF::processMemoryFile().
This commit is contained in:
James R. Barlow 2020-06-25 00:50:49 -07:00 committed by Jay Berkenbilt
parent 3221022fc9
commit 3fc7c99d02
1 changed files with 7 additions and 6 deletions
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13
libqpdf/BufferInputSource.cc
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@ -61,14 +61,15 @@ BufferInputSource::findAndSkipNextEOL()
}
qpdf_offset_t result = 0;
size_t len = QIntC::to_size(end_pos - this->m->cur_offset);
unsigned char const* buffer = this->m->buf->getBuffer();
unsigned char const* end = buffer + end_pos;
unsigned char const* p = buffer + this->m->cur_offset;
void* start = const_cast<unsigned char*>(buffer) + this->m->cur_offset;
unsigned char* p1 = static_cast<unsigned char*>(memchr(start, '\r', len));
unsigned char* p2 = static_cast<unsigned char*>(memchr(start, '\n', len));
unsigned char* p = (p1 && p2) ? std::min(p1, p2) : p1 ? p1 : p2;
if (p)
while ((p < end) && !((*p == '\r') || (*p == '\n')))
{
++p;
}
if (p < end)
{
result = p - buffer;
this->m->cur_offset = result + 1;