From 6dd5f05525d7a983e27e4db6ed125c1e63eb5c5a Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Thu, 16 Oct 2025 17:50:03 +0900
Subject: [PATCH] mruby-random: split 64-bit state into two 32-bit values on
 32-bit platforms

on 32-bit systems, the rand_state struct with uint64_t state (8 bytes,
8-byte aligned) followed by uint32_t seed_value (4 bytes) resulted in
16 bytes due to padding, exceeding the 12-byte ISTRUCT_DATA_SIZE limit.
this caused the static_assert at line 540 to fail.

split the state field into state_lo and state_hi on MRB_32BIT platforms
to achieve perfect 12-byte alignment (4+4+4) without padding. add
GET_STATE/SET_STATE macros to provide uniform access across platforms.

Co-authored-by: Claude <noreply@anthropic.com>
---
 mrbgems/mruby-random/src/random.c | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/mrbgems/mruby-random/src/random.c b/mrbgems/mruby-random/src/random.c
index f7fe32319..31765996d 100644
--- a/mrbgems/mruby-random/src/random.c
+++ b/mrbgems/mruby-random/src/random.c
@@ -38,14 +38,33 @@
 #define PCG_INCREMENT 1442695040888963407ULL
 
 typedef struct rand_state {
+#ifdef MRB_32BIT
+  /* On 32-bit platforms, split state to avoid alignment padding */
+  uint32_t state_lo;
+  uint32_t state_hi;
+#else
   uint64_t state;
+#endif
   uint32_t seed_value;  /* Track last seed for srand compatibility */
 } rand_state;
 
+/* Helper macros for 64-bit state access */
+#ifdef MRB_32BIT
+# define GET_STATE(t) (((uint64_t)(t)->state_hi << 32) | (t)->state_lo)
+# define SET_STATE(t, val) do { \
+    uint64_t v_ = (val); \
+    (t)->state_lo = (uint32_t)v_; \
+    (t)->state_hi = (uint32_t)(v_ >> 32); \
+  } while (0)
+#else
+# define GET_STATE(t) ((t)->state)
+# define SET_STATE(t, val) ((t)->state = (val))
+#endif
+
 static void
 rand_init(rand_state *t)
 {
-  t->state = 0x853c49e6748fea9bULL;
+  SET_STATE(t, 0x853c49e6748fea9bULL);
   t->seed_value = 521288629;
 }
 
@@ -57,9 +76,9 @@ rand_seed(rand_state *t, uint32_t seed)
   uint32_t old_seed = t->seed_value;
 
   /* PCG initialization: state=0, step, add seed, step, then mix */
-  t->state = 0;
+  SET_STATE(t, 0);
   rand_uint32(t);
-  t->state += seed;
+  SET_STATE(t, GET_STATE(t) + seed);
   for (int i = 0; i < 10; i++) {
     rand_uint32(t);
   }
@@ -72,10 +91,10 @@ static uint32_t
 rand_uint32(rand_state *rng)
 {
   /* PCG-XSH-RR: XorShift High (xorshift), then Random Rotate */
-  uint64_t oldstate = rng->state;
+  uint64_t oldstate = GET_STATE(rng);
 
   /* LCG step: advance internal state */
-  rng->state = oldstate * PCG_MULTIPLIER + PCG_INCREMENT;
+  SET_STATE(rng, oldstate * PCG_MULTIPLIER + PCG_INCREMENT);
 
   /* Output function: xorshift, then rotate by top bits */
   uint32_t xorshifted = (uint32_t)(((oldstate >> 18u) ^ oldstate) >> 27u);