Use rb_big_and instead of rb_big_cmp

This logic has the following merits.
* rb_big_and is exported from Ruby 1.8.7.
* it can avoid to generate a bignum object on LP64 environment
  because `LL2NUM(LLONG_MAX>>1)` is Fixnum on LP64.

Author: nurse

ext/mysql2/extconf.rb

@@ -23,7 +23,6 @@ def asplode(lib)
 have_func('rb_wait_for_single_fd')
 have_func('rb_hash_dup')
 have_func('rb_intern3')
-have_func('rb_big_cmp')
 
 # borrowed from mysqlplus
 # http://github.com/oldmoe/mysqlplus/blob/master/ext/extconf.rb

ext/mysql2/statement.c

@@ -204,39 +204,27 @@ static void set_buffer_for_string(MYSQL_BIND* bind_buffer, unsigned long *length
     xfree(length_buffers);                                  \
   }
 
-#ifndef HAVE_RB_BIG_CMP
-/* both x and y must be Bignum though MRI's rb_big_cmp support more types */
-static VALUE rb_big_cmp(VALUE x, VALUE y)
-{
-    /* Ruby 1.8.7 has rb_big_minus */
-    VALUE r = rb_big_minus(x, y);
-    if (FIXNUM_P(r)) {
-        long l = FIX2LONG(r);
-        return l < 0 ? -1 : l == 0 ? 0 : 1;
-    }
-    else { /* must be normalized Bignum */
-        return RBIGNUM_POSITIVE_P(r) ? 1 : -1;
-    }
-}
-#endif
-
 /* return 0 if the given bignum can cast as LONG_LONG, otherwise 1 */
 static int my_big2ll(VALUE bignum, LONG_LONG *ptr)
 {
     unsigned LONG_LONG num;
+    size_t len;
+    int nlz_bits = 0;
 #ifdef HAVE_RB_ABSINT_SIZE
-    if (rb_absint_size(bignum, NULL) > 8) goto overflow;
+    len = rb_absint_size(bignum, &nlz_bits);
 #else
-    if (RBIGNUM_LEN(bignum)*SIZEOF_BDIGITS > 8) goto overflow;
+    len = RBIGNUM_LEN(bignum) * SIZEOF_BDIGITS;
 #endif
+    if (len > 8) goto overflow;
     if (RBIGNUM_POSITIVE_P(bignum)) {
         num = rb_big2ull(bignum);
         if (num > LLONG_MAX)
             goto overflow;
         *ptr = num;
     }
     else {
-        if (rb_big_cmp(bignum, LL2NUM(LLONG_MIN)) == INT2FIX(-1))
+        if (len == 8 && nlz_bits == 0 &&
+                rb_big_and(bignum, LL2NUM(LLONG_MAX>>1)) != INT2FIX(0))
             goto overflow;
         *ptr = rb_big2ll(bignum);
     }

spec/mysql2/statement_spec.rb

@@ -72,9 +72,16 @@
     int64_max1 = (1 << 63)
     int64_min1 = -(1 << 63) - 1
     result = stmt.execute(int64_max1, int64_min1)
-    expect(result.to_a).to eq(['max1' => "9223372036854775808", 'min1' => "-9223372036854775809"])
+    expect(result.to_a).to eq(['max1' => int64_max1.to_s, 'min1' => int64_min1.to_s])
   end
 
+  it "should handle bignum but beyond uint64_t" do
+    stmt = @client.prepare('SELECT ? AS max1, ? AS min1')
+    int65_max1 = (1 << 64) - 1
+    int65_min1 = -(1 << 64)+1
+    result = stmt.execute(int65_max1, int65_min1)
+    expect(result.to_a).to eq(['max1' => int65_max1.to_s, 'min1' => int65_min1.to_s])
+  end
   it "should keep its result after other query" do
     @client.query 'USE test'
     @client.query 'CREATE TABLE IF NOT EXISTS mysql2_stmt_q(a int)'