将两个字符转换为一个字节

/************************************************************
将两个字符转换为一个字节，由于基本类型范围的影响，
其中包含了一种巧合即当_2asc_to_1b这个函数在转换例子中的"e1"时，
能够转换成功，因为e0转换完是2e0,由于超出了unsigned char的范围，
2将被丢弃，正好是e0.
*************************************************************/

#include <stdio.h>

unsigned char _2asc_to_1b(unsigned char* buff)
{
unsigned char b2,b1;
b2 = *(buff);
if(b2<=0x39)
b1=(b2-0x30)<<4;
else
b1=(b2-0x41+10)<<4;
b2 = *(buff+1);
if(b2<=0x39) 
b1+=(b2-0x30);
else
b1+=(b2-0x41+10);
return b1;
}

unsigned char my_2asc_to_1b(unsigned char* buff)
{
unsigned char b2,b1;
b2 = *(buff);
if(b2<=0x39)
b1=(b2-0x30)<<4;
else
b1=(b2-0x61+10)<<4;
b2 = *(buff+1);
if(b2<=0x39) 
b1+=(b2-0x30);
else
b1+=(b2-0x61+10);
return b1;
}


int main(int argc, char *argv[])
{
char *str = "10e1";
char *str1 = "ed6a";
unsigned char tar1[4] = {0};
unsigned char tar2[4] = {0};
printf("str:%s str1:%s\n",str,str1);

tar1[0] = _2asc_to_1b(str);
tar1[1] = _2asc_to_1b(str+2);

tar1[2] = _2asc_to_1b(str1);
tar1[3] = _2asc_to_1b(str1+2);
printf("_2asc:%02x%02x %02x%02x\n",tar1[0],tar1[1],tar1[2],tar1[3]);

tar2[0] = my_2asc_to_1b(str);
tar2[1] = my_2asc_to_1b(str+2);

tar2[2] = my_2asc_to_1b(str1);
tar2[3] = my_2asc_to_1b(str1+2);
printf("my_sc:%02x%02x %02x%02x\n",tar2[0],tar2[1],tar2[2],tar2[3]);

}