From 9e90e215abb213cc74a4d12c0e9374478e9b82c7 Mon Sep 17 00:00:00 2001
From: JC-000 <3798556+JC-000@users.noreply.github.com>
Date: Wed, 20 May 2026 15:34:47 -0500
Subject: [PATCH] fix(crypto/shared): mul_tables.s stub size .res 256 -> .res
 512
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Each quarter-square multiply table is 512 bytes (n in 0..510 -> 511
entries, padded to 512), not 256. Every in-the-wild implementation
across sibling libs uses 512 B per table — including this repo's own
src/data.s:136 — but the Phase C.0 stub at .res 256 would silently
truncate at n >= 256 the moment any sibling redirected its init here.

Fixes the stub before that redirect lands. No segment changes, no
API changes, no runtime change in Phase C.0 (CANONICAL_SQTAB is
not defined; the labels here stay dormant). Build verified with
default profile (BACKEND=ip65).

Refs c64-lib-contract issue #5 (size bug confirmed in audit there)
and c64-ChaCha20-Poly1305 issue #34 (the originating
sibling-ingestion thread).
---
 src/crypto/shared/mul_tables.s | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/crypto/shared/mul_tables.s b/src/crypto/shared/mul_tables.s
index 71a444f..803db77 100644
--- a/src/crypto/shared/mul_tables.s
+++ b/src/crypto/shared/mul_tables.s
@@ -15,9 +15,18 @@
 ; Public API:
 ;   mul_tables_init   - build the 256x256 quarter-square tables
 ;                       (currently: stub; returns immediately).
-;   sqtab_lo, sqtab_hi - 256-byte tables, page-aligned, in TABLES_BSS
+;   sqtab_lo, sqtab_hi - 512-byte tables each (1 KB total), page-aligned,
+;                       in TABLES_BSS. Layout `sqtab_hi = sqtab_lo + $0200`;
+;                       semantics `(sqtab_hi[n] << 8) | sqtab_lo[n] =
+;                       floor(n^2 / 4)` for n in 0..510.
 ;                       (currently: defined by src/data.s; re-homed here
-;                        under CANONICAL_SQTAB in a later phase).
+;                        under CANONICAL_SQTAB in a later phase.)
+;
+; Size note: each table is 512 bytes, not 256. The earlier stub used
+; `.res 256` which would silently truncate at n >= 256 once any sibling
+; lib redirected its init here — every in-the-wild implementation uses
+; 512 B per table (see `src/data.s:136` here, and the audit in
+; `c64-lib-contract` issue #5). Fixed before any redirect lands.
 ; =============================================================================
 
         .export mul_tables_init
@@ -41,6 +50,6 @@ mul_tables_init:
         .export sqtab_hi
 
 .segment "TABLES_BSS"
-sqtab_lo:       .res 256
-sqtab_hi:       .res 256
+sqtab_lo:       .res 512
+sqtab_hi:       .res 512
 .endif