[lmi-commits] [lmi] master fe2e852 2/6: Assume that all integer types use two's complement representation

[Greg Chicares]

branch: master
commit fe2e852e49f4fc877ca9ed1c78ef5c7320f44886
Author: Vadim Zeitlin <address@hidden>
Commit: Gregory W. Chicares <address@hidden>

    Assume that all integer types use two's complement representation
    
    This is the case in practice for all the supported platforms and two's
    complement is the only supported one since C++20, see P1236R1
    (http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1236r1.html)
---
 bourn_cast.hpp      | 4 +---
 bourn_cast_test.cpp | 4 ----
 2 files changed, 1 insertion(+), 7 deletions(-)

diff --git a/bourn_cast.hpp b/bourn_cast.hpp
index 9fec5cc..7faabc2 100644
--- a/bourn_cast.hpp
+++ b/bourn_cast.hpp
@@ -176,15 +176,13 @@ constexpr inline To bourn_cast(From from, std::true_type, 
std::false_type)
 
     From const limit = std::ldexp(From(1), to_traits::digits);
 
-    constexpr bool is_twos_complement(~To(0) == -To(1));
-
     if(std::isnan(from))
         throw std::runtime_error("Cannot cast NaN to integral.");
     if(std::isinf(from))
         throw std::runtime_error("Cannot cast infinite to integral.");
     if(!to_traits::is_signed && from < 0)
         throw std::runtime_error("Cannot cast negative to unsigned.");
-    if(from < -limit || from == -limit && !is_twos_complement)
+    if(from < -limit)
         throw std::runtime_error("Cast would transgress lower limit.");
     if(limit <= from)
         throw std::runtime_error("Cast would transgress upper limit.");
diff --git a/bourn_cast_test.cpp b/bourn_cast_test.cpp
index 17caf9e..508a1d5 100644
--- a/bourn_cast_test.cpp
+++ b/bourn_cast_test.cpp
@@ -81,10 +81,6 @@ void test_same(char const* file, int line)
     // an 80-bit long double type whose 64-bit mantissa suffices to
     // test the limits of every integral type up to 64 digits exactly
     // because it can distinguish +/-(2^64) from +/-(2^64 - 1).
-    //
-    // The signed minimum given here assumes two's complement; it
-    // would be -(x - 1) for a ones' complement or sign-and-magnitude
-    // representation.
     if(traits::is_integer)
         {
         long double const x = std::scalbln(1.0l, traits::digits);