Sprinkle some constexpr around to make Jason happy

Most of these will not matter in practice due to C++14 imposing
significant limitations on what else we can make constexpr, and we cannot
have references outliving the constexpr context either way.

src/catch2/internal/catch_uniform_integer_distribution.hpp

@@ -48,24 +48,24 @@ class uniform_integer_distribution {
     // distribution will be reused many times and this is an optimization.
     UnsignedIntegerType m_rejection_threshold = 0;
 
-    UnsignedIntegerType computeDistance(IntegerType a, IntegerType b) const {
+    static constexpr UnsignedIntegerType computeDistance(IntegerType a, IntegerType b) {
         // This overflows and returns 0 if a == 0 and b == TYPE_MAX.
         // We handle that later when generating the number.
         return transposeTo(b) - transposeTo(a) + 1;
     }
 
-    static UnsignedIntegerType computeRejectionThreshold(UnsignedIntegerType ab_distance) {
+    static constexpr UnsignedIntegerType computeRejectionThreshold(UnsignedIntegerType ab_distance) {
         // distance == 0 means that we will return all possible values from
         // the type's range, and that we shouldn't reject anything.
         if ( ab_distance == 0 ) { return 0; }
         return ( ~ab_distance + 1 ) % ab_distance;
     }
 
-    static UnsignedIntegerType transposeTo(IntegerType in) {
+    static constexpr UnsignedIntegerType transposeTo(IntegerType in) {
         return Detail::transposeToNaturalOrder<IntegerType>(
             static_cast<UnsignedIntegerType>( in ) );
     }
-    static IntegerType transposeBack(UnsignedIntegerType in) {
+    static constexpr IntegerType transposeBack(UnsignedIntegerType in) {
         return static_cast<IntegerType>(
             Detail::transposeToNaturalOrder<IntegerType>(in) );
     }
@@ -73,7 +73,7 @@ class uniform_integer_distribution {
 public:
     using result_type = IntegerType;
 
-    uniform_integer_distribution( IntegerType a, IntegerType b ):
+    constexpr uniform_integer_distribution( IntegerType a, IntegerType b ):
         m_a( transposeTo(a) ),
         m_ab_distance( computeDistance(a, b) ),
         m_rejection_threshold( computeRejectionThreshold(m_ab_distance) ) {
@@ -81,7 +81,7 @@ public:
     }
 
     template <typename Generator>
-    result_type operator()( Generator& g ) {
+    constexpr result_type operator()( Generator& g ) {
         // All possible values of result_type are valid.
         if ( m_ab_distance == 0 ) {
             return transposeBack( Detail::fillBitsFrom<UnsignedIntegerType>( g ) );
@@ -99,8 +99,8 @@ public:
         return transposeBack(m_a + emul.upper);
     }
 
-    result_type a() const { return transposeBack(m_a); }
-    result_type b() const { return transposeBack(m_ab_distance + m_a - 1); }
+    constexpr result_type a() const { return transposeBack(m_a); }
+    constexpr result_type b() const { return transposeBack(m_ab_distance + m_a - 1); }
 };
 
 } // end namespace Catch