hi all: the codes of functions is: 51 <http://lxr.oss.org.cn/source/include/asm-sh/posix_types.h?v=2.6.16#L51> #undef __FD_SET <http://lxr.oss.org.cn/ident?v=2.6.16;i=__FD_SET> 52 <http://lxr.oss.org.cn/source/include/asm-sh/posix_types.h?v=2.6.16#L52> static __inline__ void __FD_SET <http://lxr.oss.org.cn/ident?v=2.6.16;i=__FD_SET>(unsigned long __fd, __kernel_fd_set <http://lxr.oss.org.cn/ident?v=2.6.16;i=__kernel_fd_set> *__fdsetp) 53 <http://lxr.oss.org.cn/source/include/asm-sh/posix_types.h?v=2.6.16#L53> { 54 <http://lxr.oss.org.cn/source/include/asm-sh/posix_types.h?v=2.6.16#L54> unsigned long __tmp = __fd / __NFDBITS <http://lxr.oss.org.cn/ident?v=2.6.16;i=__NFDBITS>; 55 <http://lxr.oss.org.cn/source/include/asm-sh/posix_types.h?v=2.6.16#L55> unsigned long __rem = __fd % __NFDBITS <http://lxr.oss.org.cn/ident?v=2.6.16;i=__NFDBITS>; 56 <http://lxr.oss.org.cn/source/include/asm-sh/posix_types.h?v=2.6.16#L56> __fdsetp->fds_bits[__tmp] |= (1UL<<__rem); 57 <http://lxr.oss.org.cn/source/include/asm-sh/posix_types.h?v=2.6.16#L57> } I can't understand the usage of __rem,How to understand it? thank you. PS: 21 <http://lxr.oss.org.cn/source/include/linux/posix_types.h?v=2.6.16#L21> #undef __NFDBITS <http://lxr.oss.org.cn/ident?v=2.6.16;i=__NFDBITS> 22 <http://lxr.oss.org.cn/source/include/linux/posix_types.h?v=2.6.16#L22> #define __NFDBITS <http://lxr.oss.org.cn/ident?v=2.6.16;i=__NFDBITS> (8 * sizeof(unsigned long))