linux内核算法---hex_to_bin分享

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#define  tolower(c)  __tolower(c)
#define  toupper(c)  __toupper(c)

static  inline unsigned char __tolower(unsigned char c)
{
//判断字符c是否为大写英文字母 说明：当参数c为大写英文字母(A-Z)时，返回非零值，否则返回零。
if(isupper(c))
c -= 'A' - 'a' ;
return c ;
}

static inline unsigned char __toupper(unsigned char c )
{
//判断字符c是否为小写英文字母 说明：当参数c为小写英文字母(a-z)时，返回非零值，否则返回零。
if(islower(c))
c-= 'a' - 'A' ;
return c ;
}

int hex_to_bin(char ch)
{
if((ch > '0') && (ch <= '9'))
return ch - '0' ;
ch = tolower(ch) ;
if((ch >= 'a') && (ch <= 'f'))
return ch - 'a' + 10 ;
return -1 ;
}
int main(void)
{
printf("%d\n",hex_to_bin('1'));
printf("%d\n",hex_to_bin('f'));
printf("%d\n",hex_to_bin('a'));
printf("%d\n",hex_to_bin('9'));

printf("%p\n",hex_to_bin('1'));
printf("%p\n",hex_to_bin('f'));
printf("%p\n",hex_to_bin('a'));
printf("%p\n",hex_to_bin('9'));
return 0 ;
}