Unified Digest::CRC#update

[dearblue]

The generic Digest::CRC#update method is provided, eliminating the need to define separate #updates for many CRCs.
However, the Digest::CRC::REFLECT_INPUT constant must be overridden by true or false.

To speed things up a bit, the following is made:

• Use local variables instead of instance variables inside loops.
• Suppress generation of multi-precision integers.

---

I'm not particular about the name of REFLECT_INPUT, so if anyone has any suggestions, I'll change it.

[dearblue]

For reference, I am attaching the benchmark results measured on my PC.

• Please note that there are a number of background processes running, which may affect the results to some degree.
• The "real" benchmark output is taken out.
• The binary package ruby 3.2 provided by the FreeBSD project has YJIT disabled, so ruby 3.1 is used instead.
• | ruby32 -v | ruby 3.2.2 (2023-03-30 revision e51014f9c0) [amd64-freebsd13]
  | ruby31 -v | ruby 3.1.4p223 (2023-03-30 revision 957bb7cb81) [amd64-freebsd13]
  | jruby -v | jruby 9.2.17.0 (2.5.8) 2021-03-29 84d363da97 OpenJDK 64-Bit Server VM 25.372-b07 on 1.8.0_372-b07 +jit [freebsd-x86_64]

	ruby32		ruby31 --yjit		jruby
	main	this PR	main	this PR	main	this PR
Digest::CRC1#update	0.413156	0.450639	0.400173	0.392028	0.312848	0.344441
Digest::CRC5#update	1.471989	0.701404	0.682974	0.467105	0.639566	0.378853
Digest::CRC8#update	1.426721	1.002237	0.701005	0.535166	0.656496	0.438962
Digest::CRC8_1Wire#update	1.435443	0.979240	0.785536	0.530573	0.658349	0.377159
Digest::CRC15#update	1.751928	1.721342	0.779405	0.666303	0.700163	0.700162
Digest::CRC16#update	1.402283	1.339391	0.733769	0.564226	0.710644	0.406121
Digest::CRC16CCITT#update	1.740074	1.661728	0.691878	0.707596	0.740250	0.789879
Digest::CRC16DNP#update	1.341073	1.264648	0.681094	0.566660	0.512899	0.392202
Digest::CRC16Genibus#update	1.822862	1.677790	0.734139	0.706260	0.730047	0.660704
Digest::CRC16Modbus#update	1.388758	1.325434	0.712974	0.587603	0.568764	0.383336
Digest::CRC16QT#update	1.409243	1.268288	0.697429	0.566340	0.512600	0.437730
Digest::CRC16USB#update	1.394310	1.283062	0.790167	0.569061	0.552077	0.384195
Digest::CRC16X25#update	1.397066	1.323211	0.734347	0.566696	0.510791	0.417712
Digest::CRC16XModem#update	1.776022	1.782290	0.731255	0.709042	0.720106	0.665169
Digest::CRC16ZModem#update	1.810085	1.664810	0.732177	0.696851	0.673232	0.607033
Digest::CRC24#update	1.783538	1.689062	0.730286	0.667194	0.760796	0.672397
Digest::CRC32#update	1.386887	1.287927	0.723988	0.628428	0.615478	0.432369
Digest::CRC32BZip2#update	1.761105	1.711941	0.737906	0.725438	0.660596	0.661087
Digest::CRC32c#update	1.375790	1.347202	0.742967	0.597620	0.598534	0.418801
Digest::CRC32Jam#update	1.377057	1.298975	0.689968	0.575938	0.654536	0.424091
Digest::CRC32MPEG#update	1.769699	1.696188	0.761883	0.665675	0.627799	0.660462
Digest::CRC32POSIX#update	1.728269	1.660507	0.759890	0.660590	0.690486	0.688585
Digest::CRC32XFER#update	1.754600	1.678388	0.750021	0.701695	0.649378	0.688124
Digest::CRC64#update	3.504403	2.392109	2.272752	2.050897	2.108015	1.356082
Digest::CRC64Jones#update	3.461163	2.438005	2.322609	2.079037	2.145611	1.186643
Digest::CRC64XZ#update	3.447103	2.464268	2.344339	2.113575	2.077718	1.155891

[dearblue]

If we trust each element of @table, we can make just one more speed improvement:

-      crc = @crc
+      crc = @crc & ~(-1 << @width)

       if self.class::REFLECT_INPUT
         if @width > 8
           data.each_byte do |b|
-            crc = table[b ^ (0xff & crc)] ^ (crc >> 8)
+            crc = table[b ^ crc] ^ (crc >> 8)

[dearblue]

Sorry, my earlier comment is wrong.
0xff & ... can be removed in three places except above.

[postmodern]

Minor changes requested. Need a @raise YARD tag explaining when NotImplementedError will be raised. Also some specs for that logic. Also some questions about variable naming.

[postmodern]

I also noticed your using self.class::CONST. Should we replace self.class.const_get(:CONST) with self.class::CONST?

[postmodern]

I also thought about recommending code styling changes:

• Vertically align =
• Add an extra newline between assignments and data.each_byte statement.

[dearblue]

Thank you for review. I will fix it.