這個函數原理和調用？？？？C的高手看看！！！
static const char sel[] = {
'B','C','D','F','G',
'H','J','K','M','P',
'Q','R','T','V','W',
'X','Y','2','3','4',
'6','7','8','9', '\0'};
char *b24e(char *buf, unsigned char *byst, size_t sizeOfBytes)
{
int i = 0;
unsigned char *p = byst;
while ((size_t)(i = (p-byst)) < sizeOfBytes) {
buf[2*i] = sel[((*p) >> 4)];
buf[(2*i)+1] = sel[23 - ((*p) & 0x0f)];
p++;
}
buf[(2*i)+1] = '\0';
return buf;
}
unsigned char *b24d(unsigned char *buf, char *str, size_t countOfChars)
{
size_t i;
char *p = str;
char *loc[2];
unsigned char n[2];
if (countOfChars % 2)
return NULL;
for (i = 0; i < (countOfChars>>1); i++) {
loc[0] = strchr( sel, str[2*i] );
loc[1] = strchr( sel, str[ ( 2*i ) + 1 ] );
if (loc[0] == NULL || loc[1] == NULL)
return NULL;
n[0] = (unsigned char)( loc[0] - sel );
n[1] = 23 - (unsigned char)( loc[1] - sel );
buf = (unsigned char)((n[0] << 4) | n[1]);
}
return buf;
}
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