mruby-numeric-ext (int_sqrt): support bigint

include/mruby/internal.h

@@ -248,6 +248,7 @@ void mrb_gc_free_bint(mrb_state *mrb, struct RBasic *x);
 void mrb_bint_copy(mrb_state *mrb, mrb_value x, mrb_value y);
 size_t mrb_bint_memsize(mrb_value x);
 mrb_value mrb_bint_hash(mrb_state *mrb, mrb_value x);
+mrb_value mrb_bint_sqrt(mrb_state *mrb, mrb_value x);
 #endif
 
 #endif  /* MRUBY_INTERNAL_H */

mrbgems/mruby-bigint/core/bigint.c

@@ -1246,6 +1246,63 @@ mpz_gcd(mrb_state *mrb, mpz_t *gg, mpz_t *aa, mpz_t *bb)
 }
 #endif
 
+static size_t
+mpz_bit_length(const mpz_t *x)
+{
+  if (x->sz == 0 || x->sn == 0) return 0;
+
+  // 最上位 limb を取得（リトルエンディアン: 末尾）
+  size_t i = x->sz - 1;
+  mp_limb high = x->p[i];
+
+  // high の中で最上位のビットを探す
+  size_t bits = 0;
+  while (high != 0) {
+    high >>= 1;
+    bits++;
+  }
+
+  return i * (sizeof(mp_limb) * 8) + bits;
+}
+
+static void
+mpz_sqrt(mrb_state *mrb, mpz_t *z, mpz_t *x)
+{
+  mrb_assert(x->sn >= 0);
+
+  if (x->sz == 0) {
+    // sqrt(0) = 0
+    z->sn = 0;
+    z->sz = 0;
+    return;
+  }
+
+  // 初期値の設定: bit-length の半分の位置に 1 を立てる
+  size_t xbits = mpz_bit_length(x);
+  size_t sbit = (xbits + 1) / 2;
+  mpz_t s, t;
+  mpz_init_set_int(mrb, &s, 1);
+  mpz_mul_2exp(mrb, &s, &s, sbit);
+
+  mpz_init(mrb, &t);
+
+  // ループ: s = (s + x / s) / 2
+  for (;;) {
+    mpz_mdiv(mrb, &t, x, &s);     // t = x / s
+    mpz_add(mrb, &t, &t, &s);     // t = s + x/s
+    mpz_div_2exp(mrb, &t, &t, 1); // t = (s + x/s) / 2
+
+    if (mpz_cmp(mrb, &t, &s) >= 0) {
+      break; // 収束
+    }
+
+    mpz_set(mrb, &s, &t);
+  }
+
+  mpz_move(mrb, z, &s);
+  mpz_clear(mrb, &t);
+}
+
 /* --- mruby functions --- */
 /* initialize mpz_t from RBigint (not need to clear) */
 static void
@@ -2014,6 +2071,23 @@ mrb_bint_memsize(mrb_value x)
   return z.sz * sizeof(mp_limb);
 }
 
+mrb_value
+mrb_bint_sqrt(mrb_state *mrb, mrb_value x)
+{
+  mpz_t a;
+
+  bint_as_mpz(RBIGINT(x), &a);
+  if (a.sn < 0) {
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "square root of negative number");
+  }
+
+  mpz_t z;
+  mpz_init(mrb, &z);
+  mpz_sqrt(mrb, &z, &a);
+
+  return bint_norm(mrb, bint_new(mrb, &z));
+}
+
 mrb_value
 mrb_bint_hash(mrb_state *mrb, mrb_value x)
 {

mrbgems/mruby-numeric-ext/src/numeric_ext.c

@@ -283,14 +283,23 @@ isqrt(mrb_int n)
 static mrb_value
 int_sqrt(mrb_state *mrb, mrb_value self)
 {
-  mrb_int n;
-  mrb_get_args(mrb, "i", &n);
-  if (n < 0) {
-    mrb_raise(mrb, E_ARGUMENT_ERROR, "non-negative integer required");
-  }
+  mrb_value arg = mrb_get_arg1(mrb);
 
-  mrb_int result = isqrt(n);
-  return mrb_int_value(mrb, result);
+  if (mrb_integer_p(arg)) {
+    mrb_int n = mrb_integer(arg);
+    if (n < 0) {
+      mrb_raise(mrb, E_ARGUMENT_ERROR, "non-negative integer required");
+    }
+    return mrb_int_value(mrb, isqrt(n));
+  }
+#ifdef MRB_USE_BIGINT
+  else if (mrb_bigint_p(arg)) {
+    return mrb_bint_sqrt(mrb, arg);
+  }
+#endif
+  else {
+    mrb_raise(mrb, E_TYPE_ERROR, "expected Integer");
+  }
 }
 
 void