Short live q20::fill{,_n}!

It just adds constexpr to it (we're ignoring the range version).

Apply it to QStaticByteArrayMatcher, where it replaces rather
lengthy initialization code.

Pick-to: 6.4
Change-Id: I1d60216fb04c94fa66fce5cc01313b3e9ba856ac
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

2 files changed, 28 insertions, 25 deletions

diff --git a/src/corelib/global/q20algorithm.h b/src/corelib/global/q20algorithm.h
index 1d2e0117f4..69dc2d2446 100644
--- a/src/corelib/global/q20algorithm.h
+++ b/src/corelib/global/q20algorithm.h
@@ -32,6 +32,8 @@ namespace q20 {
 using std::copy;
 using std::copy_if;
 using std::copy_n;
+using std::fill;
+using std::fill_n;
 using std::is_sorted_until;
 using std::is_sorted;
 using std::transform;
@@ -75,6 +77,28 @@ copy_n(InputIterator first, Size n, OutputIterator dest)
     return dest;
 }
 
+template <typename ForwardIterator, typename Value>
+constexpr void
+fill(ForwardIterator first, ForwardIterator last, const Value &value)
+{
+    while (first != last) {
+        *first = value;
+        ++first;
+    }
+}
+
+template <typename OutputIterator, typename Size, typename Value>
+constexpr OutputIterator
+fill_n(OutputIterator first, Size n, const Value &value)
+{
+    while (n > Size{0}) {
+        *first = value;
+        ++first;
+        --n;
+    }
+    return first;
+}
+
 template <typename ForwardIterator, typename BinaryPredicate = std::less<>>
 constexpr ForwardIterator
 is_sorted_until(ForwardIterator first, ForwardIterator last, BinaryPredicate p = {})
diff --git a/src/corelib/text/qbytearraymatcher.h b/src/corelib/text/qbytearraymatcher.h
index 1ac4356e0a..1de9c23f10 100644
--- a/src/corelib/text/qbytearraymatcher.h
+++ b/src/corelib/text/qbytearraymatcher.h
@@ -6,6 +6,8 @@
 
 #include <QtCore/qbytearray.h>
 
+#include <QtCore/q20algorithm.h>
+#include <iterator>
 #include <limits>
 
 QT_BEGIN_NAMESPACE
@@ -83,31 +85,8 @@ private:
     {
         const auto uchar_max = (std::numeric_limits<uchar>::max)();
         uchar max = n > uchar_max ? uchar_max : uchar(n);
-        Skiptable table = {
-            // this verbose initialization code aims to avoid some opaque error messages
-            // even on powerful compilers such as GCC 5.3. Even though for GCC a loop
-            // format can be found that v5.3 groks, it's probably better to go with this
-            // for the time being:
-            {
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-                max, max, max, max, max, max, max, max,   max, max, max, max, max, max, max, max,
-            }
-        };
+        Skiptable table = {};
+        q20::fill(std::begin(table.data), std::end(table.data), max);
         pattern += n - max;
         while (max--)
             table.data[uchar(*pattern++)] = max;