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So you can have a constexpr (compile-time) code fragment that, say, casts a float to an unsigned int and extracts the mantissa.

Mostly though, this is fairly unimportant and tedious spec-manship, filling in some obvious gaps.

We had a version of this in chromium a few years ago. This is a proposal just picking that up from what I can tell.

Bitcast, including the specific nomenclature, comes from LLVM, which had the concept more than 10 years ago.

The concept of bitcasting is as old as programming. In the context of C++, I'm also pretty sure that the bitcast template, in one form of another, is also much older than LLVM itself.

It can be used with constexpr (http://en.cppreference.com/w/cpp/language/constexpr) to precompute values at compile time.

Here are some videos on the topic: https://www.youtube.com/watch?v=PJwd4JLYJJY https://www.youtube.com/watch?v=rpn_5Mrrxf8

I suppose to be used in constexpr functions.