stillwater-sc / universal / 25811972750

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github

Committed by web-flow

Commit Message

feat(zfpblock): full constexpr promotion of zfparray multi-block container (#831)

Completes the array layer constexpr work tracked under issue #745.
Building on the codec promotion in PR #830 (#815), zfparray<Real, Dim>
is now usable in constant-evaluated contexts -- enabling compile-time
generation of compressed scientific-data tables.

Container changes (zfparray_impl.hpp):

* All member functions annotated constexpr.  No std::is_constant_evaluated
  branching is required: every helper the container calls (encode_block,
  decode_block, zfp_bitstream, ...) is already constexpr after #815.
* _store (the std::vector<uint8_t> compressed buffer) is now mutable.
  This eliminates every const_cast<zfparray*>(this) in the const lazy-
  cache-load methods (operator(), decompress, clear_cache, load_block).
  The cache is an internal implementation detail; const methods are
  entitled to flush it.  flush() and write_back_cache() become const
  members.  Strictly safer and a const-correctness improvement.
* In-class initializers for _n, _rate, _cache, _cached_block, _dirty
  let the default constructor default to `= default` and drop the
  std::memset(_cache, 0, sizeof(_cache)) call that previously needed
  it.  All other constructors drop their memsets too.
* std::memset / std::memcpy replaced with element-wise loops throughout
  (cache copy, store copy, padded-block init).  Mechanical and reads
  identically at runtime; constexpr-safe.

Test additions (static/block/zfpblock/array/array_constexpr.cpp, NEW):

* Default-construct accessors: size, num_blocks, compressed_bytes,
  compression_ratio all constexpr-deterministic at zero state.
* Sized-rate construction: zfparray(8, 16.0) sets up 2 blocks of 4
  with 8 bytes per block -- verified via static_assert.
* Construct-from-source roundtrip: zfparray(8, 32.0, src) + decompress
  recovers powers of two within 2^-20 relative tolerance.  Exercises
  the full per-block codec at compile time through the container.
... (continued)

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