Karma: real generator off by a magnitude due to log10 rounding up

eido79 · Sep 22, 2022 · 859fd9c · 859fd9c
1 parent 5049c39
commit 859fd9c
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Showing 2 changed files with 14 additions and 1 deletion.
diff --git a/include/boost/spirit/home/karma/numeric/real_policies.hpp b/include/boost/spirit/home/karma/numeric/real_policies.hpp
@@ -258,7 +258,7 @@ namespace boost { namespace spirit { namespace karma
             // but it's spelled out to avoid inter-modular dependencies.
 
             typename remove_const<T>::type digits = 
-                (traits::test_zero(n) ? 0 : floor(log10(n))) + 1;
+                (traits::test_zero(n) ? 1 : ceil(log10(n + T(1.))));
             bool r = true;
             for (/**/; r && digits < precision_; digits = digits + 1)
                 r = char_inserter<>::call(sink, '0');

diff --git a/test/karma/real3.cpp b/test/karma/real3.cpp
@@ -36,6 +36,11 @@ namespace boost { namespace spirit { namespace traits
 }}}
 #endif
 
+struct double_prec16_policy : boost::spirit::karma::real_policies<double>
+{
+    static unsigned int precision(double) { return 16; }
+};
+
 ///////////////////////////////////////////////////////////////////////////////
 int main()
 {
@@ -185,6 +190,14 @@ int main()
         BOOST_TEST(test("1.0e-05", double_, 0.00000999999999999998));
     }
 
+    // test for #735: off by a magnitude due to log10 rounding up
+    {
+        BOOST_TEST(test("0.0999999999999998",
+            karma::real_generator<double, double_prec16_policy>(),
+            0.099999999999999770
+            ));
+    }
+
     return boost::report_errors();
 }