Don't store right end of the interval in uniform_integer_distribution

1 files changed, 10 insertions, 12 deletions

diff --git a/src/catch2/internal/catch_uniform_integer_distribution.hpp b/src/catch2/internal/catch_uniform_integer_distribution.hpp
index 3b623579..afa2015d 100644
--- a/src/catch2/internal/catch_uniform_integer_distribution.hpp
+++ b/src/catch2/internal/catch_uniform_integer_distribution.hpp
@@ -46,12 +46,12 @@ class uniform_integer_distribution {
 
     using UnsignedIntegerType = Detail::make_unsigned_t<IntegerType>;
 
-    // We store the left range bound converted to internal representation,
-    // because it will be used in computation in the () operator.
+    // Only the left bound is stored, and we store it converted to its
+    // unsigned image. This avoids having to do the conversions inside
+    // the operator(), at the cost of having to do the conversion in
+    // the a() getter. The right bound is only needed in the b() getter,
+    // so we recompute it there from other stored data.
     UnsignedIntegerType m_a;
-    // After initialization, right bound is only used for the b() getter,
-    // so we keep it in the original type.
-    IntegerType m_b;
 
     // How many different values are there in [a, b]. a == b => 1, can be 0 for distribution over all values in the type.
     UnsignedIntegerType m_ab_distance;
@@ -64,11 +64,10 @@ class uniform_integer_distribution {
     // distribution will be reused many times and this is an optimization.
     UnsignedIntegerType m_rejection_threshold = 0;
 
-    // Assumes m_b and m_a are already filled
-    UnsignedIntegerType computeDistance() const {
-        // This overflows and returns 0 if ua == 0 and ub == TYPE_MAX.
+    UnsignedIntegerType computeDistance(IntegerType a, IntegerType b) const {
+        // This overflows and returns 0 if a == 0 and b == TYPE_MAX.
         // We handle that later when generating the number.
-        return transposeTo(m_b) - m_a + 1;
+        return transposeTo(b) - transposeTo(a) + 1;
     }
 
     static UnsignedIntegerType computeRejectionThreshold(UnsignedIntegerType ab_distance) {
@@ -92,8 +91,7 @@ public:
 
     uniform_integer_distribution( IntegerType a, IntegerType b ):
         m_a( transposeTo(a) ),
-        m_b( b ),
-        m_ab_distance( computeDistance() ),
+        m_ab_distance( computeDistance(a, b) ),
         m_rejection_threshold( computeRejectionThreshold(m_ab_distance) ) {
         assert( a <= b );
     }
@@ -118,7 +116,7 @@ public:
     }
 
     result_type a() const { return transposeBack(m_a); }
-    result_type b() const { return m_b; }
+    result_type b() const { return transposeBack(m_ab_distance + m_a - 1); }
 };
 
 } // end namespace Catch