Linux 内核 0.0.1 vs 2.6.36, "ctype.h"，有什么区别？

Question

linux kernel 2.6.36从0.0.1开始效率如何

0.0.1:

1. 我明白了，在这个版本中，Linus 赋值了 c(函数的输入变量)到临时变量并对其进行操作 函数内的临时变量并返回临时变量。

2. 这发生在 tolower/toupper 函数中。

2.6.36:

1. 在 tolower/toupper 中他改变了它。
2. ctype 是常量。
3. 编写了新函数 ismask。

我想知道什么？:

为什么要进行这些更改？它带来了什么好处？

我分别列出了0.0.1和2.6.36内核版本的ctype.h文件。

 **** ctype.h, linux-0.01 *****

    #ifndef _CTYPE_H
    #define _CTYPE_H

    #define _U      0x01    /* upper */
    #define _L      0x02    /* lower */
    #define _D      0x04    /* digit */
    #define _C      0x08    /* cntrl */
    #define _P      0x10    /* punct */
    #define _S      0x20    /* white space (space/lf/tab) */
    #define _X      0x40    /* hex digit */
    #define _SP     0x80    /* hard space (0x20) */

    extern unsigned char _ctype[];
    extern char _ctmp;

    #define isalnum(c) ((_ctype+1)[c]&(_U|_L|_D))
    #define isalpha(c) ((_ctype+1)[c]&(_U|_L))
    #define iscntrl(c) ((_ctype+1)[c]&(_C))
    #define isdigit(c) ((_ctype+1)[c]&(_D))
    #define isgraph(c) ((_ctype+1)[c]&(_P|_U|_L|_D))
    #define islower(c) ((_ctype+1)[c]&(_L))
    #define isprint(c) ((_ctype+1)[c]&(_P|_U|_L|_D|_SP))
    #define ispunct(c) ((_ctype+1)[c]&(_P))
    #define isspace(c) ((_ctype+1)[c]&(_S))
    #define isupper(c) ((_ctype+1)[c]&(_U))
    #define isxdigit(c) ((_ctype+1)[c]&(_D|_X))

    #define isascii(c) (((unsigned) c)<=0x7f)
    #define toascii(c) (((unsigned) c)&0x7f)   

    #define tolower(c) (_ctmp=c,isupper(_ctmp)?_ctmp+('a'+'A'):_ctmp)
    #define toupper(c) (_ctmp=c,islower(_ctmp)?_ctmp+('A'-'a'):_ctmp)


    #endif

#

****** ctype.h, linux-2.6.36 *******

#ifndef _LINUX_CTYPE_H
#define _LINUX_CTYPE_H

/*
* NOTE! This ctype does not handle EOF like the standard C
* library is required to.
*/

#define _U      0x01    /* upper */
#define _L      0x02    /* lower */
#define _D      0x04    /* digit */
#define _C      0x08    /* cntrl */
#define _P      0x10    /* punct */
#define _S      0x20    /* white space (space/lf/tab) */
#define _X      0x40    /* hex digit */
#define _SP     0x80    /* hard space (0x20) */

extern const unsigned char _ctype[];

#define __ismask(x) (_ctype[(int)(unsigned char)(x)])

#define isalnum(c)      ((__ismask(c)&(_U|_L|_D)) != 0)
#define isalpha(c)      ((__ismask(c)&(_U|_L)) != 0)
#define iscntrl(c)      ((__ismask(c)&(_C)) != 0)
#define isdigit(c)      ((__ismask(c)&(_D)) != 0)
#define isgraph(c)      ((__ismask(c)&(_P|_U|_L|_D)) != 0)
#define islower(c)      ((__ismask(c)&(_L)) != 0)
#define isprint(c)      ((__ismask(c)&(_P|_U|_L|_D|_SP)) != 0)
#define ispunct(c)      ((__ismask(c)&(_P)) != 0)
/* Note: isspace() must return false for %NUL-terminator */
#define isspace(c)      ((__ismask(c)&(_S)) != 0)
#define isupper(c)      ((__ismask(c)&(_U)) != 0)
#define isxdigit(c)     ((__ismask(c)&(_D|_X)) != 0)

#define isascii(c) (((unsigned char)(c))<=0x7f)
#define toascii(c) (((unsigned char)(c))&0x7f)

static inline unsigned char __tolower(unsigned char c)
{
       if (isupper(c))
               c -= 'A'-'a';
       return c;
}

static inline unsigned char __toupper(unsigned char c)
{
       if (islower(c))
               c -= 'a'-'A';
       return c;
}

#define tolower(c) __tolower(c)
#define toupper(c) __toupper(c)

#endif

Answer 1

Why these changes has been made?, what good it brought home?

首先，您不必再在调用 isupper 的代码中定义 ctemp 变量，从而减少了代码行数。它还显然避免了泄露实现细节。