There are plenty of possible hashing algorithms in use. Some are forced
by standards, some are faster on hardware, some on 64-bit CPUs, some are
relatively new. So there is no single algorithm that will satisfy you in
every situation. That is why, Metalink4 files can contain many choices
of the hashes.

Various utilities, various versions, various OS distributions have
different set of available/better options. That is why meta4ra-create
and meta4ra-check utilities have -hashes option, where you specify set
of supported algorithms and command line to run for their calculation.
-hashes is comma-separated list of colon-separated "name:cmdline" pairs.
    -hashes "skein-512:skein512,sha512:libressl dgst -sha512"
option tells, that for calculation of Skein-512 you have to run skein512
command, and for SHA2-512 "libressl ..." one. They are invoked under
"/bin/sh -e -c" command, so pipelines are also allowable there. Data is
fed to their stdout and they are expected to print hash value in
hexadecimal form as a first (or single) column to stdout. First found
common algorithm is used by default for file verification in
meta4ra-check utility, so order in -hashes is important.

meta4ra-hashes-detect utility conveniently checks various predefined
known commands and outputs -hashes-compatible string for your system.

If you use "builtin" word as a command, then builtin implementation of
the hash will be used. By default, meta4ra does not require any
non-standard library dependencies, so it includes only SHA2-256 and
SHA2-512. Optionally you can run build-with-thirdparty script to enable
building with third-party libraries, including much more other hashes.

Only a few hashes are standardised:
https://www.iana.org/assignments/hash-function-text-names/hash-function-text-names.xhtml
But meta4ra uses more of advanced and performant ones. They are listed
below in order of preference.

* blake3-256
  Ultimately fast hash, still considered cryptographically secure.
  Out-of-box Merkle-tree gives ability to indefinitely parallelise for
  >1KiB blocks. It runs faster than either MD5 or hardware-accelerated
  SHA2-256. Runs several times faster with AVX512. It is reduced round
  BLAKE2s.
* blake2b-512, blake2b-256
  Very fast hash, pretty widespread as a SHA2 replacement.
  Both of its 512/256-bit variants are often met.
  It is reduced round BLAKE, that was among SHA3 finalists.
* skein-512
  Skein is fastest software hash among all SHA3 finalists, with huge
  security margin.
* shake128, shake256
  SHAKE is the officially recommended SHA3 mode of operation for general
  usage. SHAKE256 as fast as software SHA2-512 with the comparable
  security level. Can be very fast on specialised hardware.
* sha-512, sha-256
  SHA2 is rather slow, but has widespread availability. 512-bit version
  version runs faster on 64-bit CPUs. However modern CPUs have hardware
  accelerated SHA2-256, making it slower only than BLAKE3
* streebog-512, streebog-256
  Russian Federation's government standard for hashing. Both versions
  have identical speed, so 512-bit is preferred.
* xxh3-128
  XXH3 is not a cryptographically secure hash (that is why it is at the
  very end of the list), but 128-bit output with the speed of RAM makes
  it also useful for integrity checking