QString::number(int): Avoid going through qlocale machinery

For increased performance, as measured with the number_qu?longlong
QString benchmarks.

The results are all good, reducing runtime by anywhere between 40
and 220 nanoseconds. The slowest test previously completing at ~330ns,
now completing at ~105ns.

Task-number: QTBUG-88484
Change-Id: Ie96e86e57b635bac01389aed531a6d9f087df983
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 11 insertions, 2 deletions

diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index 99534cb3d1..11caefc8ec 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -7307,7 +7307,16 @@ QString QString::number(qlonglong n, int base)
         base = 10;
     }
 #endif
-    return QLocaleData::c()->longLongToString(n, -1, base);
+QT_WARNING_PUSH
+    /* "unary minus operator applied to unsigned type, result still unsigned" */
+QT_WARNING_DISABLE_MSVC(4146)
+    bool negative = n < 0;
+    /*
+      Negating std::numeric_limits<qlonglong>::min() hits undefined behavior, so
+      taking an absolute value has to cast to unsigned to change sign.
+    */
+    return qulltoBasicLatin(negative ? -qulonglong(n) : qulonglong(n), base, negative);
+QT_WARNING_POP
 }
 
 /*!
@@ -7321,7 +7330,7 @@ QString QString::number(qulonglong n, int base)
         base = 10;
     }
 #endif
-    return QLocaleData::c()->unsLongLongToString(n, -1, base);
+    return qulltoBasicLatin(n, base, false);
 }