QString: add a method to do a conversion to Latin1 without checking

If the input is already known to be Latin 1, we don't need to check and
merge in question marks. QJsonObject already needed this code, now we
can make it more efficient.

I'll need the same code in CBOR.

Change-Id: Ib48364abee9f464c96c6fffd152e508f078404e5
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

1 files changed, 7 insertions, 25 deletions

diff --git a/src/corelib/serialization/qjson_p.h b/src/corelib/serialization/qjson_p.h
index dc56a49084..feba1faac6 100644
--- a/src/corelib/serialization/qjson_p.h
+++ b/src/corelib/serialization/qjson_p.h
@@ -69,6 +69,9 @@
 
 QT_BEGIN_NAMESPACE
 
+// in qstring.cpp
+void qt_to_latin1_unchecked(uchar *dst, const ushort *uc, qsizetype len);
+
 /*
   This defines a binary data structure for Json data. The data structure is optimised for fast reading
   and minimum allocations. The whole data structure can be mmap'ed and used directly.
@@ -294,31 +297,10 @@ public:
         int len = d->length = str.length();
         uchar *l = (uchar *)d->latin1;
         const ushort *uc = (const ushort *)str.unicode();
-        int i = 0;
-#ifdef __SSE2__
-        for ( ; i + 16 <= len; i += 16) {
-            __m128i chunk1 = _mm_loadu_si128((__m128i*)&uc[i]); // load
-            __m128i chunk2 = _mm_loadu_si128((__m128i*)&uc[i + 8]); // load
-            // pack the two vector to 16 x 8bits elements
-            const __m128i result = _mm_packus_epi16(chunk1, chunk2);
-            _mm_storeu_si128((__m128i*)&l[i], result); // store
-        }
-#  ifdef Q_PROCESSOR_X86_64
-        // we can do one more round, of 8 characters
-        if (i + 8 <= len) {
-            __m128i chunk = _mm_loadu_si128((__m128i*)&uc[i]); // load
-            // pack with itself, we'll discard the high part anyway
-            chunk = _mm_packus_epi16(chunk, chunk);
-            // unaligned 64-bit store
-            qToUnaligned(_mm_cvtsi128_si64(chunk), l + i);
-            i += 8;
-        }
-#  endif
-#endif
-        for ( ; i < len; ++i)
-            l[i] = uc[i];
-        for ( ; (quintptr)(l+i) & 0x3; ++i)
-            l[i] = 0;
+        qt_to_latin1_unchecked(l, uc, len);
+
+        for ( ; (quintptr)(l+len) & 0x3; ++len)
+            l[len] = 0;
         return *this;
     }