Normalize gmp_remroot() behavior to GMP 5.1

Author: nikic

ext/gmp/gmp.c

@@ -238,6 +238,9 @@ typedef struct _gmp_temp {
 #define GMP_42_OR_NEWER \
 	((__GNU_MP_VERSION >= 5) || (__GNU_MP_VERSION >= 4 && __GNU_MP_VERSION_MINOR >= 2))
 
+#define GMP_51_OR_NEWER \
+	((__GNU_MP_VERSION >= 6) || (__GNU_MP_VERSION >= 5 && __GNU_MP_VERSION_MINOR >= 1))
+
 /* The maximum base for input and output conversions is 62 from GMP 4.2
  * onwards. */
 #if GMP_42_OR_NEWER
@@ -1607,13 +1610,14 @@ ZEND_FUNCTION(gmp_rootrem)
 	add_index_zval(return_value, 0, gmp_create(&gmpnum_result1 TSRMLS_CC));
 	add_index_zval(return_value, 1, gmp_create(&gmpnum_result2 TSRMLS_CC));
 
-#if GMP_42_OR_NEWER
+#if GMP_51_OR_NEWER
+	/* mpz_rootrem() is supported since GMP 4.2, but buggy wrt odd roots
+	 * of negative numbers */
 	mpz_rootrem(gmpnum_result1, gmpnum_result2, gmpnum_a, (unsigned long) nth);
 #else
 	mpz_root(gmpnum_result1, gmpnum_a, (unsigned long) nth);
 	mpz_pow_ui(gmpnum_result2, gmpnum_result1, (unsigned long) nth);
 	mpz_sub(gmpnum_result2, gmpnum_a, gmpnum_result2);
-	mpz_abs(gmpnum_result2, gmpnum_result2);
 #endif
 
 	FREE_GMP_TEMP(temp_a);

ext/gmp/tests/gmp_remroot.phpt

@@ -56,7 +56,7 @@ array(2) {
   [1]=>
   object(GMP)#%d (1) {
     ["num"]=>
-    string(2) "36"
+    string(3) "-36"
   }
 }
 array(2) {