Make the SHA-256 digest path allocation-free (foundation heap-discipline):
- final() and sha256_hex() now return the 64-char lowercase hex digest as
a [64]u8 by value on the stack; the cstring(64) heap allocation is gone.
- sha256_file() streams the file in fixed 64KB stack chunks via open_file/
File.read/File.close (defer-closed on every path) instead of slurping it
with read_file; peak memory is O(chunk), not O(filesize).
Tests (compare via a zero-copy string view over the [64]u8):
- 0710 updated to the by-value API (output unchanged).
- 0711 known-answer vectors: "", "abc", NIST-56/112, padding boundaries
{0,55,56,57,63,64,65,119,120}, and 1000 / 1,000,000 'a' repeats, each
pinned to its published digest (cross-checked with shasum -a 256).
- 0712 streaming equivalence (one-shot == byte-at-a-time == split-mid-block
== split-on-boundary) plus sha256_file(temp) == in-memory digest.
src/ untouched. zig build && zig build test && tests/run_examples.sh green.
Add a pure-sx streaming SHA-256 (FIPS 180-4) stdlib module, importable
as `#import "modules/std/hash.sx";`. All 32-bit word arithmetic is done
in s64 and masked back with `& MASK32`, so digests are deterministic and
platform-independent — no shelling out, no native crypto.
API:
- init() -> Sha256 (by-value *self pattern)
- update(*Sha256, string) (multi-block + partial-block buffering)
- final(*Sha256) -> string (32-byte digest as lowercase hex)
- sha256_hex(string) -> string (one-shot)
- sha256_file([:0]u8) -> ?string (digest of a file via fs.read_file)
Verified against FIPS/NIST known-answer vectors and `shasum -a 256`:
"" , "abc", the 56- and 112-byte multi-block vectors, 1000×'a', and the
64/65-byte block boundaries; chunked update() matches the one-shot call.
examples/0710-modules-sha256.sx pins the KAT vectors + the streaming
invariant; gate green (zig build, zig build test, run_examples 370/0/0/0).
