Minix中的字符判定ctype.c

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minix中关于如何判定一个字符的类型，如大写、小写、数字……
如果采用传统的方法，如判断一个字母大写的方法：

if(c>='A' && c<'Z')  return true;

但是如果判断一个字符是数字或是字母，则采用下面的代码：

if((c<'z' && c>'a') || (c<'Z' && c>'A') || (c>'0' && c<'9'))  return true

如果假设更多的局限，效率明显下降
minix的做法是定义一个256元素的unsigned char _ctypes[]数组，由于8位需要8种属性分别描述，如下：

#define _U0x01/* this bit is for upper-case letters [A-Z] */#define _L0x02/* this bit is for lower-case letters [a-z] */#define _N0x04/* this bit is for numbers [0-9] */#define _S0x08/* this bit is for white space \t \n \f etc */#define _P0x10/* this bit is for punctuation characters */#define _C0x20/* this bit is for control characters */#define _X0x40/* this bit is for hex digits [a-f] and [A-F]*/

#define_PROTOTYPE(function, params)function params

判断字符函数原型：

_PROTOTYPE( int isalnum, (int  _c)  );/* alphanumeric [a-z], [A-Z], [0-9] */_PROTOTYPE( int isalpha, (int  _c)  );/* alphabetic */_PROTOTYPE( int iscntrl, (int  _c)  );/* control characters */_PROTOTYPE( int isdigit, (int  _c)  );/* digit [0-9] */_PROTOTYPE( int isgraph, (int  _c)  );/* graphic character */_PROTOTYPE( int islower, (int  _c)  );/* lower-case letter [a-z] */_PROTOTYPE( int isprint, (int  _c)  );/* printable character */_PROTOTYPE( int ispunct, (int  _c)  );/* punctuation mark */_PROTOTYPE( int isspace, (int  _c)  );/* white space sp, \f, \n, \r, \t, \v*/_PROTOTYPE( int isupper, (int  _c)  );/* upper-case letter [A-Z] */_PROTOTYPE( int isxdigit,(int  _c)  );/* hex digit [0-9], [a-f], [A-F] */_PROTOTYPE( int tolower, (int  _c)  );/* convert to lower-case */_PROTOTYPE( int toupper, (int  _c)  );/* convert to upper-case */

以上函数都是通过宏定义：

#define isalnum(c)((__ctype+1)[c]&(_U|_L|_N))#define isalpha(c)((__ctype+1)[c]&(_U|_L))#define iscntrl(c)((__ctype+1)[c]&_C)#define isgraph(c)((__ctype+1)[c]&(_P|_U|_L|_N))#define ispunct(c)((__ctype+1)[c]&_P)#define isspace(c)((__ctype+1)[c]&_S)#define isxdigit(c)((__ctype+1)[c]&(_N|_X))#define isdigit(c)((unsigned) ((c)-'0') < 10)#define islower(c)((unsigned) ((c)-'a') < 26)#define isupper(c)((unsigned) ((c)-'A') < 26)#define isprint(c)((unsigned) ((c)-' ') < 95)#define isascii(c)((unsigned) (c) < 128)

minix将_ctype[]初始化为：

char __ctype[] = {0,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C|_S,_C|_S,_C|_S,_C|_S,_C|_S,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_C,_S,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_P,_N,_N,_N,_N,_N,_N,_N,_N,_N,_N,_P,_P,_P,_P,_P,_P,_P,_U|_X,_U|_X,_U|_X,_U|_X,_U|_X,_U|_X,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_U,_P,_P,_P,_P,_P,_P,_L|_X,_L|_X,_L|_X,_L|_X,_L|_X,_L|_X,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_P,_P,_P,_P,_C,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,};