Introduce Catch's own RNG based on the PCG family of RNGs

In the future, we will also want to introduce our own
`uniform_int_distribution` and `uniform_real_distribution` to get
repeatable test runs across different platforms.

include/internal/catch_context.cpp

@@ -7,6 +7,7 @@
  */
 #include "catch_context.h"
 #include "catch_common.h"
+#include "catch_random_number_generator.h"
 
 namespace Catch {
 
@@ -59,4 +60,11 @@ namespace Catch {
     IContext::~IContext() = default;
     IMutableContext::~IMutableContext() = default;
     Context::~Context() = default;
+
+
+    SimplePcg32& rng() {
+        static SimplePcg32 s_rng;
+        return s_rng;
+    }
+
 }

include/internal/catch_context.h

@@ -55,6 +55,9 @@ namespace Catch {
     }
 
     void cleanUpContext();
+
+    class SimplePcg32;
+    SimplePcg32& rng();
 }
 
 #endif // TWOBLUECUBES_CATCH_CONTEXT_H_INCLUDED

include/internal/catch_random_number_generator.cpp

@@ -7,23 +7,67 @@
 
 #include "catch_random_number_generator.h"
 #include "catch_context.h"
+#include "catch_run_context.h"
 #include "catch_interfaces_config.h"
 
 namespace Catch {
 
-    std::mt19937& rng() {
+namespace {
-        static std::mt19937 s_rng;
+
-        return s_rng;
+#if defined(_MSC_VER)
+#pragma warning(push)
+#pragma warning(disable:4146) // we negate uint32 during the rotate
+#endif
+        // Safe rotr implementation thanks to John Regehr
+        uint32_t rotate_right(uint32_t val, uint32_t count) {
+            const uint32_t mask = 31;
+            count &= mask;
+            return (val >> count) | (val << (-count & mask));
+        }
+
+#if defined(_MSC_VER)
+#pragma warning(pop)
+#endif
+
+}
+
+
+    SimplePcg32::SimplePcg32(result_type seed_) {
+        seed(seed_);
     }
 
-    void seedRng( IConfig const& config ) {
+
-        if( config.rngSeed() != 0 ) {
+    void SimplePcg32::seed(result_type seed_) {
-            std::srand( config.rngSeed() );
+        m_state = 0;
-            rng().seed( config.rngSeed() );
+        (*this)();
+        m_state += seed_;
+        (*this)();
+    }
+
+    void SimplePcg32::discard(uint64_t skip) {
+        // We could implement this to run in O(log n) steps, but this
+        // should suffice for our use case.
+        for (uint64_t s = 0; s < skip; ++s) {
+            static_cast<void>((*this)());
         }
     }
 
-    unsigned int rngSeed() {
+    SimplePcg32::result_type SimplePcg32::operator()() {
-        return getCurrentContext().getConfig()->rngSeed();
+        // prepare the output value
+        const uint32_t xorshifted = static_cast<uint32_t>(((m_state >> 18u) ^ m_state) >> 27u);
+        const auto output = rotate_right(xorshifted, m_state >> 59u);
+
+        // advance state
+        m_state = m_state * 6364136223846793005ULL + s_inc;
+
+        return output;
+    }
+
+    bool operator==(SimplePcg32 const& lhs, SimplePcg32 const& rhs) {
+        return lhs.m_state == rhs.m_state;
+    }
+
+    bool operator!=(SimplePcg32 const& lhs, SimplePcg32 const& rhs) {
+        return lhs.m_state != rhs.m_state;
     }
 }

include/internal/catch_random_number_generator.h

@@ -7,17 +7,52 @@
 #ifndef TWOBLUECUBES_CATCH_RANDOM_NUMBER_GENERATOR_H_INCLUDED
 #define TWOBLUECUBES_CATCH_RANDOM_NUMBER_GENERATOR_H_INCLUDED
 
-#include <algorithm>
+#include <cstdint>
-#include <random>
 
 namespace Catch {
 
-    struct IConfig;
+    // This is a simple implementation of C++11 Uniform Random Number
+    // Generator. It does not provide all operators, because Catch2
+    // does not use it, but it should behave as expected inside stdlib's
+    // distributions.
+    // The implementation is based on the PCG family (http://pcg-random.org)
+    class SimplePcg32 {
+        using state_type = std::uint64_t;
+    public:
+        using result_type = std::uint32_t;
+        static constexpr result_type min() {
+            return 0;
+        }
+        static constexpr result_type max() {
+            return static_cast<result_type>(-1);
+        }
 
-    std::mt19937& rng();
+        // Provide some default initial state for the default constructor
-    void seedRng( IConfig const& config );
+        SimplePcg32():SimplePcg32(0xed743cc4U) {}
-    unsigned int rngSeed();
 
-}
+        explicit SimplePcg32(result_type seed_);
+
+        void seed(result_type seed_);
+        void discard(uint64_t skip);
+
+        result_type operator()();
+
+    private:
+        friend bool operator==(SimplePcg32 const& lhs, SimplePcg32 const& rhs);
+        friend bool operator!=(SimplePcg32 const& lhs, SimplePcg32 const& rhs);
+
+        // In theory we also need operator<< and operator>>
+        // In practice we do not use them, so we will skip them for now
+
+
+        std::uint64_t m_state;
+        // This part of the state determines which "stream" of the numbers
+        // is chosen -- we take it as a constant for Catch2, so we only
+        // need to deal with seeding the main state.
+        // Picked by reading 8 bytes from `/dev/random` :-)
+        static const std::uint64_t s_inc = (0x13ed0cc53f939476ULL << 1ULL) | 1ULL;
+    };
+
+} // end namespace Catch
 
 #endif // TWOBLUECUBES_CATCH_RANDOM_NUMBER_GENERATOR_H_INCLUDED

include/internal/catch_run_context.cpp

@@ -506,4 +506,16 @@ namespace Catch {
         else
             CATCH_INTERNAL_ERROR("No result capture instance");
     }
+
+    void seedRng(IConfig const& config) {
+        if (config.rngSeed() != 0) {
+            std::srand(config.rngSeed());
+            rng().seed(config.rngSeed());
+        }
+    }
+
+    unsigned int rngSeed() {
+        return getCurrentContext().getConfig()->rngSeed();
+    }
+
 }

include/internal/catch_run_context.h

@@ -151,6 +151,8 @@ namespace Catch {
         bool m_includeSuccessfulResults;
     };
 
+    void seedRng(IConfig const& config);
+    unsigned int rngSeed();
 } // end namespace Catch
 
 #endif // TWOBLUECUBES_CATCH_RUNNER_IMPL_HPP_INCLUDED

include/internal/catch_test_case_registry_impl.cpp

@@ -11,6 +11,7 @@
 #include "catch_enforce.h"
 #include "catch_interfaces_registry_hub.h"
 #include "catch_random_number_generator.h"
+#include "catch_run_context.h"
 #include "catch_string_manip.h"
 #include "catch_test_case_info.h"
 

projects/CMakeLists.txt

@@ -21,6 +21,7 @@ set(TEST_SOURCES
         ${SELF_TEST_DIR}/IntrospectiveTests/GeneratorsImpl.tests.cpp
         ${SELF_TEST_DIR}/IntrospectiveTests/InternalBenchmark.tests.cpp
         ${SELF_TEST_DIR}/IntrospectiveTests/PartTracker.tests.cpp
+        ${SELF_TEST_DIR}/IntrospectiveTests/RandomNumberGeneration.tests.cpp
         ${SELF_TEST_DIR}/IntrospectiveTests/Tag.tests.cpp
         ${SELF_TEST_DIR}/IntrospectiveTests/String.tests.cpp
         ${SELF_TEST_DIR}/IntrospectiveTests/StringManip.tests.cpp

projects/SelfTest/Baselines/compact.sw.approved.txt

@@ -276,6 +276,10 @@ Tricky.tests.cpp:<line number>: passed: true
 Tricky.tests.cpp:<line number>: passed: std::vector<int>{1, 2} == std::vector<int>{1, 2} for: { 1, 2 } == { 1, 2 }
 Tricky.tests.cpp:<line number>: passed: a for: 0x<hex digits>
 Tricky.tests.cpp:<line number>: passed: a == &foo for: 0x<hex digits> == 0x<hex digits>
+RandomNumberGeneration.tests.cpp:<line number>: passed: SimplePcg32{} == SimplePcg32{} for: {?} == {?}
+RandomNumberGeneration.tests.cpp:<line number>: passed: SimplePcg32{ 0 } != SimplePcg32{} for: {?} != {?}
+RandomNumberGeneration.tests.cpp:<line number>: passed: !(SimplePcg32{ 1 } == SimplePcg32{ 2 }) for: !({?} == {?})
+RandomNumberGeneration.tests.cpp:<line number>: passed: !(SimplePcg32{ 1 } != SimplePcg32{ 1 }) for: !({?} != {?})
 Approx.tests.cpp:<line number>: passed: td == Approx(10.0) for: StrongDoubleTypedef(10) == Approx( 10.0 )
 Approx.tests.cpp:<line number>: passed: Approx(10.0) == td for: Approx( 10.0 ) == StrongDoubleTypedef(10)
 Approx.tests.cpp:<line number>: passed: td != Approx(11.0) for: StrongDoubleTypedef(10) != Approx( 11.0 )
@@ -731,6 +735,51 @@ Condition.tests.cpp:<line number>: passed: data.str_hello < "hellp" for: "hello"
 Condition.tests.cpp:<line number>: passed: data.str_hello < "zebra" for: "hello" < "zebra"
 Condition.tests.cpp:<line number>: passed: data.str_hello > "hellm" for: "hello" > "hellm"
 Condition.tests.cpp:<line number>: passed: data.str_hello > "a" for: "hello" > "a"
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 4242248763 (0x<hex digits>)
+==
+4242248763 (0x<hex digits>)
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 1867888929 (0x<hex digits>)
+==
+1867888929 (0x<hex digits>)
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 1276619030 (0x<hex digits>)
+==
+1276619030 (0x<hex digits>)
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 1911218783 (0x<hex digits>)
+==
+1911218783 (0x<hex digits>)
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 1827115164 (0x<hex digits>)
+==
+1827115164 (0x<hex digits>)
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 1472234645 (0x<hex digits>)
+==
+1472234645 (0x<hex digits>)
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 868832940 (0x<hex digits>)
+==
+868832940 (0x<hex digits>)
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 570883446 (0x<hex digits>)
+==
+570883446 (0x<hex digits>)
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 889299803 (0x<hex digits>)
+==
+889299803 (0x<hex digits>)
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 4261393167 (0x<hex digits>)
+==
+4261393167 (0x<hex digits>)
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 1472234645 (0x<hex digits>)
+==
+1472234645 (0x<hex digits>)
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 868832940 (0x<hex digits>)
+==
+868832940 (0x<hex digits>)
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 570883446 (0x<hex digits>)
+==
+570883446 (0x<hex digits>)
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 889299803 (0x<hex digits>)
+==
+889299803 (0x<hex digits>)
+RandomNumberGeneration.tests.cpp:<line number>: passed: rng() == 0x<hex digits> for: 4261393167 (0x<hex digits>)
+==
+4261393167 (0x<hex digits>)
 Message.tests.cpp:<line number>: failed: explicitly with 1 message: 'Message from section one'
 Message.tests.cpp:<line number>: failed: explicitly with 1 message: 'Message from section two'
 CmdLine.tests.cpp:<line number>: passed: spec.hasFilters() == false for: false == false

projects/SelfTest/Baselines/console.std.approved.txt

@@ -1380,6 +1380,6 @@ due to unexpected exception with message:
   Why would you throw a std::string?
 
 ===============================================================================
-test cases:  301 |  227 passed |  70 failed |  4 failed as expected
+test cases:  303 |  229 passed |  70 failed |  4 failed as expected
-assertions: 1570 | 1418 passed | 131 failed | 21 failed as expected
+assertions: 1589 | 1437 passed | 131 failed | 21 failed as expected
 

projects/SelfTest/Baselines/console.sw.approved.txt

@@ -2179,6 +2179,32 @@ Tricky.tests.cpp:<line number>: PASSED:
 with expansion:
   0x<hex digits> == 0x<hex digits>
 
+-------------------------------------------------------------------------------
+Comparison ops
+-------------------------------------------------------------------------------
+RandomNumberGeneration.tests.cpp:<line number>
+...............................................................................
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( SimplePcg32{} == SimplePcg32{} )
+with expansion:
+  {?} == {?}
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( SimplePcg32{ 0 } != SimplePcg32{} )
+with expansion:
+  {?} != {?}
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE_FALSE( SimplePcg32{ 1 } == SimplePcg32{ 2 } )
+with expansion:
+  !({?} == {?})
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE_FALSE( SimplePcg32{ 1 } != SimplePcg32{ 1 } )
+with expansion:
+  !({?} != {?})
+
 -------------------------------------------------------------------------------
 Comparison with explicitly convertible types
 -------------------------------------------------------------------------------
@@ -5494,6 +5520,125 @@ Condition.tests.cpp:<line number>: PASSED:
 with expansion:
   "hello" > "a"
 
+-------------------------------------------------------------------------------
+Our PCG implementation provides expected results for known seeds
+  Default seeded
+-------------------------------------------------------------------------------
+RandomNumberGeneration.tests.cpp:<line number>
+...............................................................................
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  4242248763 (0x<hex digits>)
+  ==
+  4242248763 (0x<hex digits>)
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  1867888929 (0x<hex digits>)
+  ==
+  1867888929 (0x<hex digits>)
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  1276619030 (0x<hex digits>)
+  ==
+  1276619030 (0x<hex digits>)
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  1911218783 (0x<hex digits>)
+  ==
+  1911218783 (0x<hex digits>)
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  1827115164 (0x<hex digits>)
+  ==
+  1827115164 (0x<hex digits>)
+
+-------------------------------------------------------------------------------
+Our PCG implementation provides expected results for known seeds
+  Specific seed
+-------------------------------------------------------------------------------
+RandomNumberGeneration.tests.cpp:<line number>
+...............................................................................
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  1472234645 (0x<hex digits>)
+  ==
+  1472234645 (0x<hex digits>)
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  868832940 (0x<hex digits>)
+  ==
+  868832940 (0x<hex digits>)
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  570883446 (0x<hex digits>)
+  ==
+  570883446 (0x<hex digits>)
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  889299803 (0x<hex digits>)
+  ==
+  889299803 (0x<hex digits>)
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  4261393167 (0x<hex digits>)
+  ==
+  4261393167 (0x<hex digits>)
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  1472234645 (0x<hex digits>)
+  ==
+  1472234645 (0x<hex digits>)
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  868832940 (0x<hex digits>)
+  ==
+  868832940 (0x<hex digits>)
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  570883446 (0x<hex digits>)
+  ==
+  570883446 (0x<hex digits>)
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  889299803 (0x<hex digits>)
+  ==
+  889299803 (0x<hex digits>)
+
+RandomNumberGeneration.tests.cpp:<line number>: PASSED:
+  REQUIRE( rng() == 0x<hex digits> )
+with expansion:
+  4261393167 (0x<hex digits>)
+  ==
+  4261393167 (0x<hex digits>)
+
 -------------------------------------------------------------------------------
 Output from all sections is reported
   one
@@ -12565,6 +12710,6 @@ Misc.tests.cpp:<line number>
 Misc.tests.cpp:<line number>: PASSED:
 
 ===============================================================================
-test cases:  301 |  211 passed |  86 failed |  4 failed as expected
+test cases:  303 |  213 passed |  86 failed |  4 failed as expected
-assertions: 1587 | 1418 passed | 148 failed | 21 failed as expected
+assertions: 1606 | 1437 passed | 148 failed | 21 failed as expected
 

projects/SelfTest/Baselines/junit.sw.approved.txt

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <testsuitesloose text artifact
 >
-  <testsuite name="<exe-name>" errors="17" failures="132" tests="1588" hostname="tbd" time="{duration}" timestamp="{iso8601-timestamp}">
+  <testsuite name="<exe-name>" errors="17" failures="132" tests="1607" hostname="tbd" time="{duration}" timestamp="{iso8601-timestamp}">
     <properties>
       <property name="filters" value="~[!nonportable]~[!benchmark]~[approvals]"/>
       <property name="random-seed" value="1"/>
@@ -242,6 +242,7 @@ Exception.tests.cpp:<line number>
     <testcase classname="<exe-name>.global" name="Character pretty printing/Low ASCII" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="Commas in various macros are allowed" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="Comparing function pointers" time="{duration}"/>
+    <testcase classname="<exe-name>.global" name="Comparison ops" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="Comparison with explicitly convertible types" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="Comparisons between ints where one side is computed" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="Comparisons between unsigned ints and negative signed ints match c++ standard behaviour" time="{duration}"/>
@@ -577,6 +578,8 @@ Condition.tests.cpp:<line number>
       </failure>
     </testcase>
     <testcase classname="<exe-name>.global" name="Ordering comparison checks that should succeed" time="{duration}"/>
+    <testcase classname="<exe-name>.global" name="Our PCG implementation provides expected results for known seeds/Default seeded" time="{duration}"/>
+    <testcase classname="<exe-name>.global" name="Our PCG implementation provides expected results for known seeds/Specific seed" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="Output from all sections is reported/one" time="{duration}">
       <failure type="FAIL">
 Message from section one

projects/SelfTest/Baselines/xml.sw.approved.txt

@@ -2529,6 +2529,41 @@ Nor would this
       </Expression>
       <OverallResult success="true"/>
     </TestCase>
+    <TestCase name="Comparison ops" tags="[rng]" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+      <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+        <Original>
+          SimplePcg32{} == SimplePcg32{}
+        </Original>
+        <Expanded>
+          {?} == {?}
+        </Expanded>
+      </Expression>
+      <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+        <Original>
+          SimplePcg32{ 0 } != SimplePcg32{}
+        </Original>
+        <Expanded>
+          {?} != {?}
+        </Expanded>
+      </Expression>
+      <Expression success="true" type="REQUIRE_FALSE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+        <Original>
+          !(SimplePcg32{ 1 } == SimplePcg32{ 2 })
+        </Original>
+        <Expanded>
+          !({?} == {?})
+        </Expanded>
+      </Expression>
+      <Expression success="true" type="REQUIRE_FALSE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+        <Original>
+          !(SimplePcg32{ 1 } != SimplePcg32{ 1 })
+        </Original>
+        <Expanded>
+          !({?} != {?})
+        </Expanded>
+      </Expression>
+      <OverallResult success="true"/>
+    </TestCase>
     <TestCase name="Comparison with explicitly convertible types" tags="[Approx]" filename="projects/<exe-name>/UsageTests/Approx.tests.cpp" >
       <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/UsageTests/Approx.tests.cpp" >
         <Original>
@@ -6728,6 +6763,165 @@ Nor would this
       </Expression>
       <OverallResult success="true"/>
     </TestCase>
+    <TestCase name="Our PCG implementation provides expected results for known seeds" tags="[rng]" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+      <Section name="Default seeded" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            4242248763 (0x<hex digits>)
+==
+4242248763 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            1867888929 (0x<hex digits>)
+==
+1867888929 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            1276619030 (0x<hex digits>)
+==
+1276619030 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            1911218783 (0x<hex digits>)
+==
+1911218783 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            1827115164 (0x<hex digits>)
+==
+1827115164 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <OverallResults successes="5" failures="0" expectedFailures="0"/>
+      </Section>
+      <Section name="Specific seed" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            1472234645 (0x<hex digits>)
+==
+1472234645 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            868832940 (0x<hex digits>)
+==
+868832940 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            570883446 (0x<hex digits>)
+==
+570883446 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            889299803 (0x<hex digits>)
+==
+889299803 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            4261393167 (0x<hex digits>)
+==
+4261393167 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            1472234645 (0x<hex digits>)
+==
+1472234645 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            868832940 (0x<hex digits>)
+==
+868832940 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            570883446 (0x<hex digits>)
+==
+570883446 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            889299803 (0x<hex digits>)
+==
+889299803 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <Expression success="true" type="REQUIRE" filename="projects/<exe-name>/IntrospectiveTests/RandomNumberGeneration.tests.cpp" >
+          <Original>
+            rng() == 0x<hex digits>
+          </Original>
+          <Expanded>
+            4261393167 (0x<hex digits>)
+==
+4261393167 (0x<hex digits>)
+          </Expanded>
+        </Expression>
+        <OverallResults successes="10" failures="0" expectedFailures="0"/>
+      </Section>
+      <OverallResult success="true"/>
+    </TestCase>
     <TestCase name="Output from all sections is reported" tags="[.][failing][messages]" filename="projects/<exe-name>/UsageTests/Message.tests.cpp" >
       <Section name="one" filename="projects/<exe-name>/UsageTests/Message.tests.cpp" >
         <Failure filename="projects/<exe-name>/UsageTests/Message.tests.cpp" >
@@ -14923,7 +15117,7 @@ loose text artifact
       </Section>
       <OverallResult success="true"/>
     </TestCase>
-    <OverallResults successes="1418" failures="149" expectedFailures="21"/>
+    <OverallResults successes="1437" failures="149" expectedFailures="21"/>
   </Group>
-  <OverallResults successes="1418" failures="148" expectedFailures="21"/>
+  <OverallResults successes="1437" failures="148" expectedFailures="21"/>
 </Catch>

projects/SelfTest/IntrospectiveTests/RandomNumberGeneration.tests.cpp

@@ -0,0 +1,45 @@
+/*
+ *  Created by Martin on 06/10/2019.
+ *
+ *  Distributed under the Boost Software License, Version 1.0. (See accompanying
+ *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+ */
+
+#include "catch.hpp"
+
+#include "internal/catch_random_number_generator.h"
+
+TEST_CASE("Our PCG implementation provides expected results for known seeds", "[rng]") {
+    Catch::SimplePcg32 rng;
+    SECTION("Default seeded") {
+        REQUIRE(rng() == 0xfcdb943b);
+        REQUIRE(rng() == 0x6f55b921);
+        REQUIRE(rng() == 0x4c17a916);
+        REQUIRE(rng() == 0x71eae25f);
+        REQUIRE(rng() == 0x6ce7909c);
+    }
+    SECTION("Specific seed") {
+        rng.seed(0xabcd1234);
+        REQUIRE(rng() == 0x57c08495);
+        REQUIRE(rng() == 0x33c956ac);
+        REQUIRE(rng() == 0x2206fd76);
+        REQUIRE(rng() == 0x3501a35b);
+        REQUIRE(rng() == 0xfdffb30f);
+
+        // Also check repeated output after reseeding
+        rng.seed(0xabcd1234);
+        REQUIRE(rng() == 0x57c08495);
+        REQUIRE(rng() == 0x33c956ac);
+        REQUIRE(rng() == 0x2206fd76);
+        REQUIRE(rng() == 0x3501a35b);
+        REQUIRE(rng() == 0xfdffb30f);
+    }
+}
+
+TEST_CASE("Comparison ops", "[rng]") {
+    using Catch::SimplePcg32;
+    REQUIRE(SimplePcg32{} == SimplePcg32{});
+    REQUIRE(SimplePcg32{ 0 } != SimplePcg32{});
+    REQUIRE_FALSE(SimplePcg32{ 1 } == SimplePcg32{ 2 });
+    REQUIRE_FALSE(SimplePcg32{ 1 } != SimplePcg32{ 1 });
+}