[lmi-commits] [lmi] master aaf4595 2/4: Ascertain identity element for std::max() and std::min()

[Greg Chicares]

branch: master
commit aaf4595a4da3faa7cda97a82497c1066170ad47d
Author: Gregory W. Chicares <gchicares@sbcglobal.net>
Commit: Gregory W. Chicares <gchicares@sbcglobal.net>

    Ascertain identity element for std::max() and std::min()
    
    "supremum" means LUB, and "infimum" means GLB. Chose these terms not
    because of their precise mathematical definitions but because the terms
    "max" and especially "min" have been spoiled by the Standard: DBL_MAX
    is not maximal because it's less than positive infinity; and DBL_MIN
    is greater than most doubles because it is not even negative, and it is
    not even the lowest positive double, as denorm_min() < min().
---
 miscellany.hpp      | 22 ++++++++++++++++++++++
 miscellany_test.cpp | 14 ++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/miscellany.hpp b/miscellany.hpp
index 56c5e64..f101e5a 100644
--- a/miscellany.hpp
+++ b/miscellany.hpp
@@ -83,6 +83,28 @@ std::string floating_rep(T t)
     return oss.str();
 }
 
+template<typename T>
+constexpr T infimum()
+{
+    using limits = std::numeric_limits<T>;
+    static_assert(limits::is_bounded);
+    if constexpr(limits::has_infinity)
+        return -limits::infinity();
+    else
+        return limits::min();
+}
+
+template<typename T>
+constexpr T supremum()
+{
+    using limits = std::numeric_limits<T>;
+    static_assert(limits::is_bounded);
+    if constexpr(limits::has_infinity)
+        return limits::infinity();
+    else
+        return limits::max();
+}
+
 /// Ascertain vector minimum and maximum efficiently.
 ///
 /// Heterogeneous relational operators are necessarily free functions.
diff --git a/miscellany_test.cpp b/miscellany_test.cpp
index f3390a0..6c68916 100644
--- a/miscellany_test.cpp
+++ b/miscellany_test.cpp
@@ -26,6 +26,7 @@
 #include "test_tools.hpp"
 
 #include <cfloat>                       // DBL_MAX
+#include <cmath>                        // HUGE_VAL
 #include <cstdio>                       // remove()
 #include <fstream>
 #include <limits>
@@ -131,6 +132,18 @@ void test_files_are_identical()
     std::remove(f1);
 }
 
+void test_sup_inf()
+{
+    LMI_TEST_EQUAL( false   , infimum <bool  >());
+    LMI_TEST_EQUAL( true    , supremum<bool  >());
+    LMI_TEST_EQUAL( INT_MIN , infimum <int   >());
+    LMI_TEST_EQUAL( INT_MAX , supremum<int   >());
+    LMI_TEST_EQUAL(-HUGE_VAL, infimum <double>());
+    LMI_TEST_EQUAL( HUGE_VAL, supremum<double>());
+
+    LMI_TEST_EQUAL( 0       , infimum <unsigned int>());
+}
+
 void test_minmax()
 {
     double const zero = 0.0;
@@ -412,6 +425,7 @@ int test_main(int, char*[])
 {
     test_each_equal();
     test_files_are_identical();
+    test_sup_inf();
     test_minmax();
     test_prefix_and_suffix();
     test_scale_power();