Experiment: replace lua´s string hash with luajits ARX hash

the string hashing was the most hit and most spent in part of the whole game in alot of cases
replacing it with luajits algo absolutely massively improves lua performance (10-15fps in my bench timedemos!)
however idk how all this stuff exactly works so this needs alot of testing to make sure nothing breaks
ive rewritten the unaligned ptr access slightly to use memcpy for safety with some platforms that require stricter alignment

src/blua/lstring.c

@@ -72,13 +72,63 @@ static TString *newlstr (lua_State *L, const char *str, size_t l,
 }
 
 
-TString *luaS_newlstr (lua_State *L, const char *str, size_t l) {
-  GCObject *o;
+// string hash taken from luaJIT
+
+/* Unaligned load of uint32_t. */
+static inline __attribute__((always_inline)) uint32_t getu32(const void* ptr)
+{
+  uint32_t result;
+  memcpy(&result, ptr, 4);
+  return result;
+}
+
+// smol macro to look a little less messy lul
+#define getu8(p) *cast(const uint8_t *, p)
+
+/* Keyed sparse ARX string hash. Constant time. */
+static unsigned hash_sparse(const char *str, size_t len)
+{
+  /* Constants taken from lookup3 hash by Bob Jenkins. */
+  unsigned int a, b, h = cast(unsigned int, len);
+#define rol(x, n) (((x)<<(n)) | ((x)>>(-cast(int, n)&(8*sizeof(x)-1))))
+  if (len >= 4) {  /* Caveat: unaligned access! */
+    a  = getu32(str);
+    h ^= getu32(str+len-4);
+    b  = getu32(str+(len>>1)-2);
+    h ^= b; h -= rol(b, 14);
+    b += getu32(str+(len>>2)-1);
+  } else {
+    a  = getu8(str);
+    h ^= getu8(str+len-1);
+    b  = getu8(str+(len>>1));
+    h ^= b; h -= rol(b, 14);
+  }
+  a ^= h; a -= rol(h, 11);
+  b ^= a; b -= rol(a, 25);
+  h ^= b; h -= rol(b, 16);
+#undef rol
+  return h;
+}
+
+#undef getu8
+
+
+static inline __attribute__((always_inline)) unsigned luaS_hash (const char *str, size_t l) {
+#if 0
   unsigned int h = cast(unsigned int, l);  /* seed */
   size_t step = (l>>5)+1;  /* if string is too long, don't hash all its chars */
   size_t l1;
   for (l1=l; l1>=step; l1-=step)  /* compute hash */
     h = h ^ ((h<<5)+(h>>2)+cast(unsigned char, str[l1-1]));
+  return h;
+#else
+  return hash_sparse(str, l);
+#endif
+}
+
+TString *luaS_newlstr (lua_State *L, const char *str, size_t l) {
+  GCObject *o;
+  unsigned int h = luaS_hash(str, l);
   for (o = G(L)->strt.hash[lmod(h, G(L)->strt.size)];
        o != NULL;
        o = o->gch.next) {