<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> </head> <body> <div style="word-wrap:break-word"> <div class="x_BodyFragment"> <div class="x_PlainText"> Your bigint library has a bug when compiled on a mac using the -O2 flag with Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn). In particular, Line 115 of BigInteger::convertToSignedPrimitive() X x = -X(b); doesn’t behave as expected when compiled at the -O2 level. Compile the attached C++ sample on a mac using clang/llvm to see exactly what goes wrong. I fixed this bug and added 64-bit tests. You will find the fixes/improvements here: <a href="https://github.com/kurmasz/bigint">https://github.com/kurmasz/bigint</a> Zack Kurmas </div> </div> <div class="x_BodyFragment"> <div class="x_PlainText"> -- Zachary Kurmas Assistant Professor of Computer Science Grand Valley State University <a href="http://www.cis.gvsu.edu/~kurmasz">http://www.cis.gvsu.edu/~kurmasz</a> —— #include <iostream> template<class Out> Out negate(unsigned long in) { // This line casts an unsigned long to a signed long. // 2^63 as an unsigned long is 0x8000000000000000 // Casting 2^63 from unsigned long to signed long should // produce -2^63 (which is also 0x8000000000000000). // The twos complement of -2^63 just happens to be -2^63, // so, (long)(2^63) should always be -2^63, correct? // This code works as expected when compiled with gcc 4.4.7; but, // when compiled on a mac with -O2 using LLVM 5.1 / clang-503.0.40, // it produces the wrong answer. (The source of the problem is // clearly visible in the generated assembly code.) Out out = -Out(in); if (out > 0) { std::cout << "Oops!" << std::endl; } else { std::cout << "Correct." << std::endl; } return out; } int main() { unsigned long in = 9223372036854775808UL; std::cout << "Attempt 3: " << std::endl; negate<long>(in); } </div> </div> </div> <div style="word-wrap:break-word"></div> </body> </html>