#include <stdlib.h>
long a64l(const char *s);
These functions maintain numbers stored in base64 ASCII characters that define a notation by which long integers can be represented by up to six characters. Each character represents a "digit" in a radix64 notation.
The characters used to represent "digits" are as follows:

The a64l() function takes a pointer to a nullterminated base64 representation and returns a corresponding long value. If the string pointed to by s contains more than six characters, a64l() uses the first six.
The a64l() function scans the character string from left to right with the least significant digit on the left, decoding each character as a 6bit radix64 number.
The l64a() function takes a long argument and returns a pointer to the corresponding base64 representation. If the argument is 0, l64a() returns a pointer to a null string.
The value returned by l64a() is a pointer into a static buffer, the contents of which are overwritten by each call. In the case of multithreaded applications, the return value is a pointer to thread specific data.
See attributes(5) for descriptions of the following attributes:
ATTRIBUTE TYPE  ATTRIBUTE VALUE 
Interface Stability  Standard 
MTLevel  MTSafe 
attributes(5), standards(5)