diff --git a/array.c b/array.c
index a19e7bb..0c0e3fb 100755
--- a/array.c
+++ b/array.c
@@ -4766,6 +4766,51 @@ rb_ary_shuffle(int argc, VALUE *argv, VALUE ary)
 }
 
 
+struct sample_with_memo_arg {
+    VALUE randgen, ary;
+    long len, n;
+    st_table *memo;
+    VALUE result;
+};
+
+static VALUE
+sample_with_memo(VALUE a)
+{
+    struct sample_with_memo_arg *arg = (void *)a;
+    VALUE randgen = arg->randgen;
+    long i, j, i2, j2, len;
+    st_data_t value;
+    RARRAY_PTR_USE(arg->result, ptr_result, {
+	for (i=0; i<arg->n; i++) {
+	    ptr_result[i] = RAND_UPTO(arg->len-i) + i;
+	}
+	len = RARRAY_LEN(arg->ary);
+	if (len < arg->len) {
+	    for (i=0; i<arg->n; i++) {
+		if ((long)ptr_result[i] >= len) arg->n = 0;
+	    }
+	    if (arg->n > len) arg->n = len;
+	}
+	for (i=0; i<arg->n; i++) {
+	    j2 = j = ptr_result[i];
+	    i2 = i;
+	    if (st_lookup(arg->memo, (st_data_t)i, &value)) i2 = (long)value;
+	    if (st_lookup(arg->memo, (st_data_t)j, &value)) j2 = (long)value;
+	    st_insert(arg->memo, (st_data_t)j, (st_data_t)i2);
+	    ptr_result[i] = rb_ary_elt(arg->ary, j2);
+	}
+    });
+    return Qnil;
+}
+
+static VALUE
+ensure_sample_with_memo(VALUE arg)
+{
+    st_free_table((st_table*)arg);
+    return Qnil;
+}
+
+
 /*
  *  call-seq:
  *     ary.sample                  -> obj
@@ -4875,6 +4920,13 @@ rb_ary_sample(int argc, VALUE *argv, VALUE ary)
 	    }
 	});
     }
+    else if (n <= (len<2560 ? len/128 : len<5120 ? len/64 : len<10240 ? len/32 : len/16)) {
+	struct sample_with_memo_arg arg = { randgen, ary, len, n };
+	arg.memo = st_init_numtable_with_size(n);
+	result = arg.result = rb_ary_new_capa(n);
+	rb_ensure(sample_with_memo, (VALUE)&arg, ensure_sample_with_memo, (VALUE)arg.memo);
+	n = arg.n;
+    }
     else {
 	result = rb_ary_dup(ary);
 	RBASIC_CLEAR_CLASS(result);