Hashing library — CRC32 / MD5 / SHA-256 (known-vector test app)

• Type: feature
• Status: done
• Owner: —
• Opened: 2026-06-19
• Closed: 2026-06-20
• Relation: demo-eligible-as-library from idea-demo-app-candidates (new catalog entry — strongest pure oracle). Sibling to feature-json-library et al. Exercises the bit-twiddling lane; pairs with the bit-packing work in feature-rtl-conversion-and-bitset-library. Own unit, FPC-ish naming, no port.

Goal

A Hashing unit providing checksum / digest functions over byte buffers and strings: CRC32, MD5, SHA256 (SHA-1 optional). Return raw digest bytes plus a hex-string helper.

Surface (sketch)

• function CRC32(const buf; len): LongWord;
• function MD5(const buf; len): TMD5Digest; / SHA256(...) : TSHA256Digest;
• string overloads + DigestToHex(d): AnsiString
• streaming context (Init/Update/Final) optional, second slice

Coverage

UInt32 / Int64 bit ops (rotate / shr / xor / and — rotate especially stresses codegen) · large static const tables (K-constants, CRC table) · byte arrays / buffer handling · careful width + endianness. No float, tiny, ESP32-perfect.

Acceptance / oracle

• Published test vectors: SHA256("") = e3b0c442..., MD5("abc") = 900150983..., known CRC32 values — exact, impossible to fake, no reference renderer needed.
• Byte-identical digests across all targets (real test of 32/64-bit bit codegen).
• Demo: examples/hashing/ prints digests of a fixed input set vs embedded expected values.

Notes

• These are integrity/checksum primitives. Not a password-storage or key-derivation recommendation — that is a separate concern if it ever arises.

Constraints

Own .pas unit; FPC-ish naming (cf. FPC md5 / sha1 units) but our own impl; no port; no self-host / cross regression.

Log

• 2026-06-19 — Opened from the demo/library organization pass.
• 2026-06-20 — Landed lib/rtl/hashing.pas with CRC32* (streaming + chunk) and Adler32 (commit 1bd5c47). Used by the new zlib and png units. Wired into lib-test / library-suite-green via test/lib_zlib.pas and test/lib_png.pas.