QString: optimize number() and setNum()

Previously, number() was implemented in terms of setNum().

That makes no sense whatsoever. It creates a temporary
value which requires the function to have an exception
table and an unwinding trampoline. It also introduces
a default constructor (in number()) and a copy assignment
(in setNum()), which breaks the chain of RVOs originating
in the QLocaleData functions.

Instead, implement setNum() in terms of number().

This makes setNum() such a premature pessimisation that
it's probably best to deprecate it in the near future.
There are not many users of it in qtbase left, and it
just pollutes the QString interface.

Effects on Linux GCC 4.9 stripped release builds:
 text   -708B
 data    +-0B
 relocs  +-0

Change-Id: I015c9ddb1ba9c98c2c55e38e54ef7894954ac4ca
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>

1 files changed, 46 insertions, 63 deletions

diff --git a/src/corelib/tools/qstring.cpp b/src/corelib/tools/qstring.cpp
index 5d8b5a6af5..aa35d764fa 100644
--- a/src/corelib/tools/qstring.cpp
+++ b/src/corelib/tools/qstring.cpp
@@ -6398,14 +6398,7 @@ float QString::toFloat(bool *ok) const
 */
 QString &QString::setNum(qlonglong n, int base)
 {
-#if defined(QT_CHECK_RANGE)
-    if (base < 2 || base > 36) {
-        qWarning("QString::setNum: Invalid base (%d)", base);
-        base = 10;
-    }
-#endif
-    *this = QLocaleData::c()->longLongToString(n, -1, base);
-    return *this;
+    return *this = number(n, base);
 }
 
 /*!
@@ -6413,14 +6406,7 @@ QString &QString::setNum(qlonglong n, int base)
 */
 QString &QString::setNum(qulonglong n, int base)
 {
-#if defined(QT_CHECK_RANGE)
-    if (base < 2 || base > 36) {
-        qWarning("QString::setNum: Invalid base (%d)", base);
-        base = 10;
-    }
-#endif
-    *this = QLocaleData::c()->unsLongLongToString(n, -1, base);
-    return *this;
+    return *this = number(n, base);
 }
 
 /*! \fn QString &QString::setNum(short n, int base)
@@ -6451,32 +6437,7 @@ QString &QString::setNum(qulonglong n, int base)
 
 QString &QString::setNum(double n, char f, int prec)
 {
-    QLocaleData::DoubleForm form = QLocaleData::DFDecimal;
-    uint flags = 0;
-
-    if (qIsUpper(f))
-        flags = QLocaleData::CapitalEorX;
-    f = qToLower(f);
-
-    switch (f) {
-        case 'f':
-            form = QLocaleData::DFDecimal;
-            break;
-        case 'e':
-            form = QLocaleData::DFExponent;
-            break;
-        case 'g':
-            form = QLocaleData::DFSignificantDigits;
-            break;
-        default:
-#if defined(QT_CHECK_RANGE)
-            qWarning("QString::setNum: Invalid format char '%c'", f);
-#endif
-            break;
-    }
-
-    *this = QLocaleData::c()->doubleToString(n, prec, form, -1, flags);
-    return *this;
+    return *this = number(n, f, prec);
 }
 
 /*!
@@ -6514,9 +6475,7 @@ QString &QString::setNum(double n, char f, int prec)
 
 QString QString::number(long n, int base)
 {
-    QString s;
-    s.setNum(n, base);
-    return s;
+    return number(qlonglong(n), base);
 }
 
 /*!
@@ -6526,9 +6485,7 @@ QString QString::number(long n, int base)
 */
 QString QString::number(ulong n, int base)
 {
-    QString s;
-    s.setNum(n, base);
-    return s;
+    return number(qulonglong(n), base);
 }
 
 /*!
@@ -6536,9 +6493,7 @@ QString QString::number(ulong n, int base)
 */
 QString QString::number(int n, int base)
 {
-    QString s;
-    s.setNum(n, base);
-    return s;
+    return number(qlonglong(n), base);
 }
 
 /*!
@@ -6546,9 +6501,7 @@ QString QString::number(int n, int base)
 */
 QString QString::number(uint n, int base)
 {
-    QString s;
-    s.setNum(n, base);
-    return s;
+    return number(qulonglong(n), base);
 }
 
 /*!
@@ -6556,9 +6509,13 @@ QString QString::number(uint n, int base)
 */
 QString QString::number(qlonglong n, int base)
 {
-    QString s;
-    s.setNum(n, base);
-    return s;
+#if defined(QT_CHECK_RANGE)
+    if (base < 2 || base > 36) {
+        qWarning("QString::setNum: Invalid base (%d)", base);
+        base = 10;
+    }
+#endif
+    return QLocaleData::c()->longLongToString(n, -1, base);
 }
 
 /*!
@@ -6566,9 +6523,13 @@ QString QString::number(qlonglong n, int base)
 */
 QString QString::number(qulonglong n, int base)
 {
-    QString s;
-    s.setNum(n, base);
-    return s;
+#if defined(QT_CHECK_RANGE)
+    if (base < 2 || base > 36) {
+        qWarning("QString::setNum: Invalid base (%d)", base);
+        base = 10;
+    }
+#endif
+    return QLocaleData::c()->unsLongLongToString(n, -1, base);
 }
 
 
@@ -6586,9 +6547,31 @@ QString QString::number(qulonglong n, int base)
 */
 QString QString::number(double n, char f, int prec)
 {
-    QString s;
-    s.setNum(n, f, prec);
-    return s;
+    QLocaleData::DoubleForm form = QLocaleData::DFDecimal;
+    uint flags = 0;
+
+    if (qIsUpper(f))
+        flags = QLocaleData::CapitalEorX;
+    f = qToLower(f);
+
+    switch (f) {
+        case 'f':
+            form = QLocaleData::DFDecimal;
+            break;
+        case 'e':
+            form = QLocaleData::DFExponent;
+            break;
+        case 'g':
+            form = QLocaleData::DFSignificantDigits;
+            break;
+        default:
+#if defined(QT_CHECK_RANGE)
+            qWarning("QString::setNum: Invalid format char '%c'", f);
+#endif
+            break;
+    }
+
+    return QLocaleData::c()->doubleToString(n, prec, form, -1, flags);
 }
 
 namespace {