FFI: Add 64 bit integer arithmetic.

src/lj_cdata.c

@@ -230,4 +230,44 @@ void lj_cdata_set(CTState *cts, CType *d, uint8_t *dp, TValue *o, CTInfo qual)
   lj_cconv_ct_tv(cts, d, dp, o, 0);
 }
 
+/* -- 64 bit integer arithmetic helpers ----------------------------------- */
+
+/* 64 bit integer x^k. */
+uint64_t lj_cdata_powi64(uint64_t x, uint64_t k, int isunsigned)
+{
+  uint64_t y = 0;
+  int sign = 0;
+  if (k == 0)
+    return 1;
+  if (!isunsigned) {
+    if ((int64_t)k < 0) {
+      if (x == 0)
+	return U64x(7fffffff,ffffffff);
+      else if (x == 1)
+	return 1;
+      else if ((int64_t)x == -1)
+	return (k & 1) ? -1 : 1;
+      else
+	return 0;
+    }
+    if ((int64_t)x < 0) {
+      x = -x;
+      sign = (k & 1);
+    }
+  }
+  for (; (k & 1) == 0; k >>= 1) x *= x;
+  y = x;
+  if ((k >>= 1) != 0) {
+    for (;;) {
+      x *= x;
+      if (k == 1) break;
+      if (k & 1) y *= x;
+      k >>= 1;
+    }
+    y *= x;
+  }
+  if (sign) y = (uint64_t)-(int64_t)y;
+  return y;
+}
+
 #endif