The other thread mentioned Marsaglia’s xorshf generator, but no one posted the code. static unsigned long x=123456789, y=362436069, z=521288629; unsigned long xorshf96(void) { //period 2^96-1 unsigned long t; x ^= x << 16; x ^= x >> 5; x ^= x << 1; t = x; x = y; y = z; z = t …
As I understand it, the purpose of signaling NaN is to initialize data structures, but, of course runtime initialization in C runs the risk of having the NaN loaded into a float register as part of initialization, thereby triggering the signal because the the compiler isn’t aware that this float value needs to be copied …
Update: Thanks to Faisal Vali and Richard Smith, this bug has been corrected in Clang ToT; see the test file introduced by the commit. According to ยง8.5.1 [dcl.init.aggr] it appears that Clang is wrong: 11/ Braces can be elided in an initializer-list as follows. If the initializer-list begins with a left brace, then the succeeding …
UPDATE: Following the discussion in the comments, I added some more evidence at the end of this answer. Disclaimer: I admit this answer is rather speculative. The current formulation of the C++11 Standard, on the other hand, does not seem to allow for a more formal answer. In the context of this Q&A, it has …
Why the current attempts fail std::tie(a, b) produces a std::tuple<int&, string&>. This type is not related to std::tuple<int, string> etc. std::tuple<T…>s have several assignment-operators: A default assignment-operator, that takes a std::tuple<T…> A tuple-converting assignment-operator template with a type parameter pack U…, that takes a std::tuple<U…> A pair-converting assignment-operator template with two type parameters U1, U2, …
Well, there is one obvious reason: because it wouldn’t do everything that bit_cast does. Even in the C++20 world where we can allocate memory at compile time, reinterpret_cast is forbidden in constexpr functions. One of the explicit goals of bit_cast is to be able to do these sorts of things at compile-time: Furthermore, it is …
It turned out that this approach does not entirely work when compiling a debuggable library. The release library is compiled with -O2 which optimizes out some infelicities, but the debug library is done with -O0 which reveals some additional problems. Furthermore, I wasn’t too happy about having to edit the boost files. So with some …
This is CWG active issue 2118: Defining a friend function in a template, then referencing that function later provides a means of capturing and retrieving metaprogramming state. This technique is arcane and should be made ill-formed. Notes from the May, 2015 meeting: CWG agreed that such techniques should be ill-formed, although the mechanism for prohibiting …
Given the most simple working example I can think of: 2 classes, a and b, where a depends on b . . a.h #ifndef A_H #define A_H class aclass { public: int method(int x, int y); }; #endif a.cpp #include “a.h” #include “b.h” int aclass::method(int x, int y) { bclass b; return x * b.method(x,y); …
There is no X object, living or otherwise, so pretending that there is one results in undefined behavior. [intro.object]/1 spells out exhaustively when objects are created: An object is created by a definition ([basic.def]), by a new-expression ([expr.new]), when implicitly changing the active member of a union ([class.union]), or when a temporary object is created …