下列常量由此扩展定义，且仅在此扩展编译入 PHP 或在运行时动态载入时可用。
GMP_ROUND_ZERO
(int)
GMP_ROUND_PLUSINF
(int)
GMP_ROUND_MINUSINF
(int)
GMP_MSW_FIRST
(int)
GMP_LSW_FIRST
(int)
GMP_LITTLE_ENDIAN
(int)
GMP_BIG_ENDIAN
(int)
GMP_NATIVE_ENDIAN
(int)
GMP_VERSION
(string)