Compact descriptor of a peptide instance held by the FragmentIndex.
Field semantics and how they relate to the braced initializer lists used in tests {a, b, {c, d}, e}:
- protein_idx .......... 'a' Index into the FASTA entries vector passed to build(); identifies the source protein.
- mod_bitmask_ ......... 'b' Bitmask encoding which variable modification slots are active. Each bit corresponds to a (position, mod_type) pair found by scanning the sequence left-to-right against the variable modification config. 0 = unmodified (or fixed-only). Supports up to 32 variable mod slots.
- sequence_ ............ '{c, d}' 0-based start offset and length (in residues) of the peptide subsequence within the protein. Note: length (d) is used like std::string::substr(start, length).
- precursor_mz_ ........ 'e' Mono-isotopic m/z at charge 1 (M+H)+; used for ordering/slicing in the index. Many tests use a dummy value here since only ordering invariants are asserted.