The phased compression driver was computing the schedule/round
*index* per iteration and then shifting it left by 2 to get the
byte offset (`schedule_one(i << 2)`, `round_one(r << 2)`). The
shift compiles to two ASLs per iteration — cheap, but pure dead
work since the byte offset is just the previous one + 4.
Track the byte offset as the loop counter and bump it by 4 each
iteration. The schedule and round APIs already wanted byte
offsets, so the call sites also get a touch shorter (no more
intermediate `var i: u8 = first_idx + step`).
Strict cycle savings are tiny — a handful per iteration — so
this is more about not leaving obviously redundant work in the
inner loop than a meaningful perf win. Hash output unchanged
(still AE9145DB…4E0D for "NES"); no other examples affected;
emulator harness 34/34.
https://claude.ai/code/session_01FRmSBruVWCufm3LsUVMs8v
An end-to-end FIPS 180-4 SHA-256 hasher running entirely on the NES.
The player types up to 16 ASCII characters on a 5x8 on-screen
keyboard, presses Enter, and the program computes and displays the
64-character hex digest.
Layout (`examples/sha256/*.ne`):
constants.ne layout + K[64] / H_INIT[8] tables
(declared as `var` with init_array because the
v0.1 compiler treats `const u8[N] = [...]` as
a no-op — noted in the file)
assets.ne 44-tile Tileset (A..Z, 0..9, punctuation,
special keys, cursor) shared between BG and
sprite layers
background.ne static nametable (title, labels, keyboard
grid) painted at reset
state.ne globals
sha_core.ne 32-bit byte primitives (copy, xor, and, add,
not, rotr, shr) in inline asm + sigma/Sigma
mixers + schedule/round steps + fold
render.ne OAM helpers for cursor, input buffer, and
64-nibble digest
keyboard.ne key dispatch table
entering_state.ne cursor navigation + typing + auto-demo
computing_state.ne phased driver (48 schedule steps + 64 rounds
+ fold across ~30 frames at 4 iterations each)
showing_state.ne renders the 256-bit digest as 8 rows of 8
sprite glyphs
Implementation notes:
- All 32-bit words live as 4 little-endian bytes in `wk[64]`,
`w[256]`, `h_state[32]` so every primitive walks four bytes with
`LDA {arr},X`/`STA {arr},X` chains and, for adds, a carry chain.
- Every primitive reads its parameters straight out of the
transport slots `$04`/`$05` rather than `{dst}`/`{src}`
substitutions: the inline-asm resolver looks parameters up in
the analyzer's allocation table but the codegen spills them to a
different per-function RAM slot, so `{dst}` would resolve to a
ZP slot nothing ever writes to. Bypassing the substitution
entirely sidesteps the issue without a compiler change.
- Rotate-right by any amount is a byte-rotate loop plus a bit-
rotate loop so the 10 SHA amounts (2, 6, 7, 11, 13, 17, 18, 19,
22, 25) all compile to a handful of chained `ROR`s.
- The headless jsnes golden auto-types "NES" after 1 s of idle and
captures its SHA-256 digest
AE9145DB5CABC41FE34B54E34AF8881F462362EA20FD8F861B26532FFBB84E0D
— byte-identical to `shasum` / `hashlib.sha256(b"NES")`.
Build: `cargo run --release -- build examples/sha256.ne`
https://claude.ai/code/session_01FRmSBruVWCufm3LsUVMs8v
