Now that we've flipped the C++20 switch, let's start making use of
the nice new <bit> header.
I'm planning on handling this move away from BitUtils.h incrementally
in a series of PRs. There may be a few functions remaining in
BitUtils.h by the end that C++20 doesn't have any equivalents for.
SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.
These are bit manipulation functions, so they belong within BitUtils.
This also gets rid of duplicated code and avoids relying on compiler
reserved names existing or not existing to determine whether or not we
define a set of functions.
Optimizers are smart enough in GCC and clang to transform the code to a
ROR or ROL instruction in the respective functions.
In a particular hashing heavy scene in Crazy Taxi the Murmur3 hash used 3.11% CPU time.
The new CRC32 hash in the same scene used 1.86%
This was tested on a Nvidia SHIELD Android TV with Cortex-A57s.
This will be a bit slower on the Nexus 9, the Denver CPU core is a bit slower with CRC32 texture hashing than Murmur3 texture hashing.
If we are compiling in the CRC32 hash, clang has an issue with casting a s32 to a u64.
Change our lens argument to a unsigned integer to fix the issue.
Our defines were never clear between what meant 64bit or x86_64
This makes a clear cut between bitness and architecture.
This commit also has the side effect of bringing up aarch64 compiling support.
