Avoid calling gettimeofday every time through the benchmarking loop, by keeping
track of how long each loop takes and doubling the number of iterations done
between time checks when they take less than 1/16'th of the total elapsed time.

- ensure header namespaces and end comments are correct
- add missing header end comments
- ensure minimal formatting (add newlines etc.)

Zcash: left out change to src/policy/policy.h which we don't yet have.

Add benchmarks for the cryptographic hash algorithms:

- RIPEMD160
- SHA1
- SHA256
- SHA512

Continues work on #7883.

Previously the benchmark code used an integer division (%) with
 a non-constant in the inner-loop.  This is quite slow on many
 processors, especially ones like ARM that lack a hardware divide.

Even on fairly recent x86_64 like haswell an integer division can
 take something like 100 cycles-- making it comparable to the
 runtime of siphash.

This change avoids the division by using bitmasking instead. This
 was especially easy since the count was only increased by doubling.

This change also restarts the timing when the execution time was
 very low this avoids mintimes of zero in cases where one execution
 ends up below the timer resolution. It also reduces the impact of
 the overhead on the final result.

The formatting of the prints is changed to not use scientific
 notation make it more machine readable (in particular, gnuplot
 croaks on the non-fixedpoint, and it doesn't sort correctly).

This also hoists out all the floating point divisions out of the
 semi-hot path because it was easy to do so.

It might be prudent to break out the critical test into a macro
 just to guarantee that it gets inlined.  It might also make sense
 to just save out the intermediate counts and times and get the
 floating point completely out of the timing loop (because e.g.
 on hardware without a fast hardware FPU like some ARM it will
 still be slow enough to distort the results). I haven't done
 either of these in this commit.

There are only a few uses of `insecure_random` outside the tests.
This PR replaces uses of insecure_random (and its accompanying global
state) in the core code with an FastRandomContext that is automatically
seeded on creation.

This is meant to be used for inner loops. The FastRandomContext
can be in the outer scope, or the class itself, then rand32() is used
inside the loop. Useful e.g. for pushing addresses in CNode or the fee
rounding, or randomization for coin selection.

As a context is created per purpose, thus it gets rid of
cross-thread unprotected shared usage of a single set of globals, this
should also get rid of the potential race conditions.

- I'd say TxMempool::check is not called enough to warrant using a special
  fast random context, this is switched to GetRand() (open for
  discussion...)

- The use of `insecure_rand` in ConnectThroughProxy has been replaced by
  an atomic integer counter. The only goal here is to have a different
  credentials pair for each connection to go on a different Tor circuit,
  it does not need to be random nor unpredictable.

- To avoid having a FastRandomContext on every CNode, the context is
  passed into PushAddress as appropriate.

There remains an insecure_random for test usage in `test_random.h`.

Zcash: Resolved conflicts with the following files

	src/addrman.cpp
	src/main.cpp
	src/net.cpp
	src/net.h
	src/policy/fees.cpp
	src/policy/fees.h
	src/random.cpp
	src/test/merkle_tests.cpp
	src/test/net_tests.cpp
	src/test/prevector_tests.cpp
	src/test/sighash_tests.cpp
	src/test/skiplist_tests.cpp
	src/test/test_bitcoin.cpp
	src/test/versionbits_tests.cpp
	src/wallet/test/crypto_tests.cpp

Make sure that the count is a zero modulo the new mask before
scaling, otherwise the next time until a measure triggers
will take only 1/2 as long as accounted for. This caused
the 'min time' to be potentially off by as much as 100%.

This adds cycle min/max/avg to the statistics.

Supported on x86 and x86_64 (natively through rdtsc), as well as Linux
(perf syscall).

…ce files.

Zcash: Only apply changes to src/bench/bench.cpp

…c numbers, fixed scoping of vectors (and memory movement component of benchmark).

The initialization order of global data structures in different
implementation units is undefined. Making use of this is essentially
gambling on what the linker does, the so-called [Static initialization
order fiasco](https://isocpp.org/wiki/faq/ctors#static-init-order).

In this case it apparently worked on Linux but failed on OpenBSD and
FreeBSD.

To create it on first use, make the registration structure local to
a function.

Fixes #8910.

…lly unreachable

Zcash: Only applied changes to src/bench/

Avoid static analyzer warnings regarding "Function call argument
is a pointer to uninitialized value" in cases where we are
intentionally using such arguments.

This is achieved by using ...

`f(b.begin(), b.end())` (`std::array<char, N>`)

... instead of ...

`f(b, b + N)` (`char b[N]`)

Rationale:
* Reduce false positives by guiding static analyzers regarding our
  intentions.

Before this commit:

```
$ clang-tidy-3.5 -checks=* src/bench/base58.cpp
bench/base58.cpp:23:9: warning: Function call argument is a pointer to uninitialized value [clang-analyzer-core.CallAndMessage]
        EncodeBase58(b, b + 32);
        ^
$ clang-tidy-3.5 -checks=* src/bench/verify_script.cpp
bench/verify_script.cpp:59:5: warning: Function call argument is a pointer to uninitialized value [clang-analyzer-core.CallAndMessage]
    key.Set(vchKey, vchKey + 32, false);
    ^
$
```

After this commit:

```
$ clang-tidy-3.5 -checks=* src/bench/base58.cpp
$ clang-tidy-3.5 -checks=* src/bench/verify_script.cpp
$
```

Zcash: Only applied changes to src/bench/base58.cpp

…etprecision

We were saving a div by caching the inverse as a float, but this
ended up requiring a int -> float -> int conversion, which takes
almost as much time as the difference between float mul and div.

There are lots of other more pressing issues with the bench
framework which probably require simply removing the adaptive
iteration count stuff anyway.

std::chrono removes portability issues.

Rather than storing doubles, store the untouched time_points. Then
convert to nanoseconds for display. This allows for maximum precision, while
keeping results comparable between differing hardware/operating systems.

Also, display full nanosecond counts rather than sub-second floats.