On this website each file has .txt added to its name (spsin.ts.txt is spsin.ts) so it opens as plain text.

# Apollo 11 SPSIN / SPCOS: modernisation and equivalence test

Evidence behind the blog post "ProductSphere and the Apollo 11 Code: A Modernisation Case Study".
Run on 22 October 2026.

## What was done

1. **Source.** `chrislgarry/Apollo-11` (commit 911e5c0). 175 `.agc` files: 85 in Comanche055, 90 in Luminary099.
2. **Assembly.** The full Luminary099 program assembled with Virtual AGC's `yaYUL` (virtualagc commit faca381) with
   0 fatal errors. The repository's `MAIN.agc` names two files differently from the files on disk
   (`LAMBERT_AIMPOINT_GUIDANCE.agc`, `TRIM_GIMBAL_CNTROL_SYSTEM.agc`); copies under those names were added in a work directory only.
3. **Binary check.** The assembled rope was compared word for word with Virtual AGC's proofread
   `Luminary099.binsource` (and `AP11ROPE.binsource`, which is identical to it). 4 words differ, all in banks 21 and 33.
   Bank 02, which holds SPSIN and SPCOS (05032–05071) and their constants, is identical. The test runs the proofread rope.
4. **Original run.** `run_sp.c` drives Virtual AGC's CPU core (`yaAGC/agc_engine.c`) through SPSIN (05033) and SPCOS (05032)
   for all 32,768 15-bit inputs, interrupts off, watchdogs reset before each call.
5. **Rewrite.** `spsin.ts`: the same polynomial, flight constants and AGC rounding rules, in TypeScript.
6. **Test.** `equivalence.test.ts` compares each rewrite with every original result.

## Results

| Rewrite | Calls | Mismatches |
|---|---|---|
| `Math.sin` / `Math.cos`, rounded | 65,536 | 43,250 (sin 21,666, cos 21,584), worst 4 LSB |
| `spsin.ts` (from intent) | 65,536 | **0** |

Planted bugs, each caught: doubling after truncation (32,488 calls), mirror point 32767 (20,850), rounding multiplies (22,976).

Facts about the original: it never returns negative zero or overflows; its worst error against true sine is 4.17 LSB (1 LSB = 1/16,384).

## Other source checks used in the post

- NOVAC is defined in both `Comanche055/EXECUTIVE.agc:37` and `Luminary099/EXECUTIVE.agc:37`.
- KILLTASK is defined only in Luminary099 and called from 11 places (BURN_BABY_BURN 630, 797; P20-P25 952, 997, 1187, 1215, 2706, 3207, 4301, 4379, 4386).
- SPSIN/SPCOS are called from 10 places: GPMATRIX (T4RUPT_PROGRAM), QUICTRIG (POWERED_FLIGHT_SUBROUTINES), GOTANGLS (P20-P25).
- "TEMPORARY, I HOPE HOPE HOPE": `Luminary099/LUNAR_LANDING_GUIDANCE_EQUATIONS.agc:179`.

## Re-running

```sh
git clone https://github.com/chrislgarry/Apollo-11
git clone https://github.com/virtualagc/virtualagc        # yaYUL, yaAGC, Tools/oct2bin, Luminary099/*.binsource
make -C virtualagc/yaYUL cc=cc
cc -O2 '-DNVER="local"' -o oct2bin virtualagc/Tools/oct2bin.c virtualagc/Tools/utils.c
./oct2bin < virtualagc/Luminary099/Luminary099.binsource && mv oct2bin.bin lum099.bin
cc -O2 -w -Ivirtualagc/yaAGC -o run_sp run_sp.c stubs.c virtualagc/yaAGC/agc_engine.c virtualagc/yaAGC/agc_engine_init.c virtualagc/yaAGC/NullAPI.c
./run_sp lum099.bin 5033 5032 > sp_original.txt
node equivalence.test.ts sp_original.txt
```