From 0a5e4cf1b05dcba55188a2c5b9ee09afa7ba8bbe Mon Sep 17 00:00:00 2001
From: Mark Olesen <Mark.Olesen@esi-group.com>
Date: Fri, 19 Jan 2018 17:13:03 +0100
Subject: [PATCH] ENH: define stdFoam::min(), stdFoam::max() as constexpr as
 per C++14

---
 applications/test/bitops/Test-bitops.C | 90 ++++++++++++++++++++++----
 src/OpenFOAM/include/stdFoam.H         | 17 ++++-
 2 files changed, 92 insertions(+), 15 deletions(-)

diff --git a/applications/test/bitops/Test-bitops.C b/applications/test/bitops/Test-bitops.C
index dd3c2b03ac..fa0dfb63bd 100644
--- a/applications/test/bitops/Test-bitops.C
+++ b/applications/test/bitops/Test-bitops.C
@@ -28,36 +28,57 @@ Description
 
 #include "bool.H"
 #include "IOstreams.H"
+#include "stdFoam.H"
 
 #include <algorithm>
 #include <type_traits>
 #include <limits>
 
+
+namespace Foam
+{
+namespace Detail
+{
+
 template<typename UIntType, UIntType v, unsigned int n>
-struct set_lower_bits
+struct bitops_setlower
 :
-    public std::integral_constant
+    std::integral_constant
     <
         UIntType,
-        v | (v >> n) | set_lower_bits<UIntType, v | (v >> n), (n >> 1)>::value
+        v | (v >> n) | bitops_setlower<UIntType, v | (v >> n), (n >> 1)>::value
     >
 {};
 
-
 template<typename UIntType, UIntType v>
-struct set_lower_bits<UIntType, v, 1>
+struct bitops_setlower<UIntType, v, 1>
 :
-    public std::integral_constant<UIntType, v | (v >> 1)>
+    std::integral_constant<UIntType, v | (v >> 1)>
 {};
 
 
+template<size_t N>
+struct bitops_topbit
+:
+    std::integral_constant
+    <
+        size_t,
+        bitops_topbit<(N >> 1)>{} + 1
+    >
+{};
+
+template<> struct bitops_topbit<2> : std::integral_constant<size_t,1> {};
+template<> struct bitops_topbit<1> : std::integral_constant<size_t,1> {};
+template<> struct bitops_topbit<0> : std::integral_constant<size_t,0> {};
+
+
 template<typename UIntType, UIntType v>
 struct pow2ceil
 :
     public std::integral_constant
     <
         UIntType,
-        set_lower_bits
+        bitops_setlower
         <
             UIntType,
             v - 1,
@@ -66,22 +87,53 @@ struct pow2ceil
     >
 {};
 
-
-// No quite
 template<size_t N>
-struct topbit : std::integral_constant<size_t, topbit<(N >> 1)>{} + 1> {};
+struct pow2ceil_shift
+:
+    std::integral_constant
+    <
+        size_t,
+        bitops_topbit<pow2ceil<size_t, N>::value>::value
+    >
+{};
+
+}
+}
+
+
+template<typename UIntType, UIntType v>
+struct pow2ceil
+:
+    Foam::Detail::pow2ceil<UIntType,v>
+{};
+
+
+template<size_t N>
+struct pow2topbit
+:
+    Foam::Detail::pow2ceil_shift<N>
+{};
 
-template<> struct topbit<1> : std::integral_constant<size_t,1> {};
-template<> struct topbit<0> : std::integral_constant<size_t,0> {};
 
 using namespace Foam;
 
-
 template<size_t N>
 void printTopbit()
 {
     std::cout
-        <<"topbit<" << N << "> : " << topbit<N>::value << '\n';
+        << "pow2ceil<" << N << "> = "
+        << pow2ceil<size_t, N>::value
+        << " shift = " << pow2topbit<N>::value << '\n';
+}
+
+
+template<class T, int Offset = 19>
+void printOffset()
+{
+    std::cout
+        << "pow2ceil of " << typeid(T).name() << " <" << sizeof(T) << "> = "
+        << pow2ceil<size_t, sizeof(T)>::value
+        << " shift = " << pow2topbit<sizeof(T)>::value << '\n';
 }
 
 
@@ -114,6 +166,16 @@ int main(int argc, char *argv[])
     printTopbit<16>();
     printTopbit<17>();
     printTopbit<18>();
+    printTopbit<29>();
+    printTopbit<30>();
+    printTopbit<31>();
+    printTopbit<32>();
+    printTopbit<33>();
+    printTopbit<4095>();
+    printTopbit<4096>();
+    printTopbit<4097>();
+
+    printOffset<double>();
 
     Info << "---\nEnd\n" << endl;
 
diff --git a/src/OpenFOAM/include/stdFoam.H b/src/OpenFOAM/include/stdFoam.H
index ac6bd6c342..916d8baddf 100644
--- a/src/OpenFOAM/include/stdFoam.H
+++ b/src/OpenFOAM/include/stdFoam.H
@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2017 OpenCFD Ltd.
+    \\  /    A nd           | Copyright (C) 2017-2018 OpenCFD Ltd.
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -155,6 +155,21 @@ constexpr auto crend(const C& c) -> decltype(c.rend())
     return c.rend();
 }
 
+//- Return the lesser of the parameters.
+//  Definition as per std::min C++14
+template<class T>
+constexpr inline const T& min(const T& a, const T& b)
+{
+    return (b < a) ? b : a;
+}
+
+//- Return the greater of the parameters.
+//  Definition as per std::max C++14
+template<class T>
+constexpr inline const T& max(const T& a, const T& b)
+{
+    return (a < b) ? b : a;
+}
 
 } // End namespace stdFoam