corwin/card-game.el
1
0
Fork 0
Code Issues Pull requests Projects Releases 1 Packages Wiki Activity Actions

cg-core: make cg-shuffle optionally seeded and reproducible

Browse source 
cg-shuffle gains an optional SEED and a `cg-shuffle-seed' dynamic var.
With a seed the order is deterministic and identical on every platform,
so a deal can be replayed, shared between players, or pinned in a test;
the index comes from secure-hash (spec-defined output everywhere, 7 hex
digits stay a fixnum even on 32-bit Emacs), so no bignum/overflow
behaviour can vary it.  With no seed the shuffle is the byte-for-byte
old system-random path -- normal play is unchanged.

Test cgt-shuffle-seeded pins determinism, permutation, override and a
cross-platform golden prefix; fails on the prior one-arg cg-shuffle.
Suite 159/159.
This commit is contained in:
Corwin Brust 2026-08-03 22:18:02 -05:00
parent 1a59003b13
commit 6379127e17
8 changed files with 180 additions and 15 deletions
Download patch file Download diff file Expand all files Collapse all files

20
test/card-games-tests.el
View file

@ -262,6 +262,26 @@ known :type built from plain data; anything else never reaches
(setcdr (cdr cyc) cyc)
(should-not (cg-net--valid-p (list :type 'move :move cyc) '(hello move)))))
;;;; Seeded shuffle
(ert-deftest cgt-shuffle-seeded ()
"A seeded shuffle is deterministic, portable, and a true permutation;
the unseeded shuffle keeps its system-random behaviour. Opening #4."
(let ((deck (number-sequence 0 51)))
;; same seed -> identical order (FAILS on HEAD: cg-shuffle takes 1 arg)
(should (equal (cg-shuffle deck 12345) (cg-shuffle deck 12345)))
;; still a permutation of the input, nothing dropped or duplicated
(should (equal (sort (copy-sequence (cg-shuffle deck 12345)) #'<) deck))
;; different seeds -> different order (almost surely)
(should-not (equal (cg-shuffle deck 1) (cg-shuffle deck 2)))
;; the dynamic variable seeds it too, and an explicit seed overrides it
(should (equal (let ((cg-shuffle-seed "deal-A")) (cg-shuffle deck))
(let ((cg-shuffle-seed "deal-A")) (cg-shuffle deck))))
(should (equal (cg-shuffle deck 7)
(let ((cg-shuffle-seed "ignored")) (cg-shuffle deck 7))))
;; portability pin: this exact prefix must hold on every platform
(should (equal (seq-take (cg-shuffle deck "GOLDEN") 6) '(15 20 35 24 31 23)))))
;;;; Gaps
(ert-deftest cgt-gaps-deal ()