Add numeric_cast template for numeric conversion

This is for now only applied to mp_integer but could be extended to
other numerical types.

Author: romainbrenguier

src/util/mp_arith.h

@@ -12,8 +12,10 @@ Author: Daniel Kroening, [email protected]
 
 #include <string>
 #include <iosfwd>
+#include <limits>
 
 #include "big-int/bigint.hh"
+#include "optional.h"
 
 // NOLINTNEXTLINE(readability/identifiers)
 typedef BigInt mp_integer;
@@ -48,9 +50,83 @@ const std::string integer2string(const mp_integer &, unsigned base=10);
 const mp_integer string2integer(const std::string &, unsigned base=10);
 const std::string integer2binary(const mp_integer &, std::size_t width);
 const mp_integer binary2integer(const std::string &, bool is_signed);
+
+/// \deprecated use numeric_cast<unsigned long long> instead
 mp_integer::ullong_t integer2ulong(const mp_integer &);
+
+/// \deprecated use numeric_cast<std::size_t> instead
 std::size_t integer2size_t(const mp_integer &);
+
+/// \deprecated use numeric_cast<unsigned> instead
 unsigned integer2unsigned(const mp_integer &);
+
 const mp_integer mp_zero=string2integer("0");
 
+/// Numerical cast provides a unified way of converting from one numerical type
+/// to another.
+/// Generic case doesn't exist, this has to be specialized for different types.
+template <typename T, typename = void>
+struct numeric_castt final
+{
+};
+
+/// Convert mp_integer to any signed type
+/// \tparam T: type to convert to
+/// \param mpi: mp_integer to convert
+/// \return optional integer of type T if conversion is possible,
+///         empty optional otherwise.
+template <typename T>
+struct numeric_castt<T,
+                     typename std::enable_if<std::is_integral<T>::value &&
+                                             std::is_signed<T>::value>::type>
+{
+  static optionalt<T> numeric_cast(const mp_integer &mpi)
+  {
+    static_assert(
+      std::numeric_limits<T>::max() <=
+          std::numeric_limits<decltype(mpi.to_long())>::max() &&
+        std::numeric_limits<T>::min() >=
+          std::numeric_limits<decltype(mpi.to_long())>::min(),
+      "Numeric cast only works for types smaller than long long");
+    if(
+      mpi <= std::numeric_limits<T>::max() &&
+      mpi >= std::numeric_limits<T>::min())
+      // to_long converts to long long which is the largest signed numeric type
+      return {static_cast<T>(mpi.to_long())};
+    else
+      return {};
+  }
+};
+
+/// Convert mp_integer to any unsigned type
+/// \tparam T: type to convert to
+/// \param mpi: mp_integer to convert
+/// \return optional integer of type T if conversion is possible,
+///         empty optional otherwise.
+template <typename T>
+struct numeric_castt<T,
+                     typename std::enable_if<std::is_integral<T>::value &&
+                                             !std::is_signed<T>::value>::type>
+{
+  static optionalt<T> numeric_cast(const mp_integer &mpi)
+  {
+    static_assert(
+      std::numeric_limits<T>::max() <=
+          std::numeric_limits<decltype(mpi.to_ulong())>::max() &&
+        std::numeric_limits<T>::min() >=
+          std::numeric_limits<decltype(mpi.to_ulong())>::min(),
+      "Numeric cast only works for types smaller than unsigned long long");
+    if(mpi <= std::numeric_limits<T>::max() && mpi >= 0)
+      return {static_cast<T>(mpi.to_ulong())};
+    else
+      return {};
+  }
+};
+
+template <typename T>
+optionalt<T> numeric_cast(const mp_integer &mpi)
+{
+  return numeric_castt<T>::numeric_cast(mpi);
+}
+
 #endif // CPROVER_UTIL_MP_ARITH_H