Fixed zerodiv/moduloofone FN for '1/std::expm1(0)'

cfg/std.cfg

@@ -1447,7 +1447,7 @@
   <function name="expm1,std::expm1">
     <use-retval/>
     <pure/>
-    <returnValue type="double"/>
+    <returnValue type="double">expm1(arg1)</returnValue>
     <noreturn>false</noreturn>
     <leak-ignore/>
     <arg nr="1" direction="in">
@@ -1458,7 +1458,7 @@
   <function name="expm1f,std::expm1f">
     <use-retval/>
     <pure/>
-    <returnValue type="float"/>
+    <returnValue type="float">expm1(arg1)</returnValue>
     <noreturn>false</noreturn>
     <leak-ignore/>
     <arg nr="1" direction="in">
@@ -1469,7 +1469,7 @@
   <function name="expm1l,std::expm1l">
     <use-retval/>
     <pure/>
-    <returnValue type="long double"/>
+    <returnValue type="long double">expm1(arg1)</returnValue>
     <noreturn>false</noreturn>
     <leak-ignore/>
     <arg nr="1" direction="in">

lib/programmemory.cpp

@@ -796,6 +796,17 @@ static std::unordered_map<std::string, BuiltinLibraryFunction> createBuiltinLibr
         v.valueType = ValueFlow::Value::ValueType::FLOAT;
         return v;
     };
+    functions["expm1"] = [](const std::vector<ValueFlow::Value>& args) {
+        if (args.size() != 1)
+            return ValueFlow::Value::unknown();
+        ValueFlow::Value v = args[0];
+        if (!v.isFloatValue() && !v.isIntValue())
+            return ValueFlow::Value::unknown();
+        double value = args[0].isFloatValue() ? args[0].floatValue : args[0].intvalue;
+        v.floatValue = std::exp2(value);
+        v.valueType = ValueFlow::Value::ValueType::FLOAT;
+        return v;
+    };
     functions["log"] = [](const std::vector<ValueFlow::Value>& args) {
         if (args.size() != 1)
             return ValueFlow::Value::unknown();

test/cfg/std.cpp

@@ -141,6 +141,13 @@ int moduloofone_cos()
     return 42 % i;
 }
 
+int moduloofone_expm1()
+{
+    int i = std::expm1(0);
+    // cppcheck-suppress moduloofone
+    return 42 % i;
+}
+
 int moduloofone_exp()
 {
     int i = std::exp(0);