2.2 a64l, l64a—convert between radix-64 ASCII string and long

Synopsis

#include <stdlib.h>
long a64l(const char *input);
char *l64a(long input);

Description
Conversion is performed between long and radix-64 characters. The l64a routine transforms up to 32 bits of input value starting from least significant bits to the most significant bits. The input value is split up into a maximum of 5 groups of 6 bits and possibly one group of 2 bits (bits 31 and 30).

Each group of 6 bits forms a value from 0–63 which is translated into a character as follows:

• 0 = ’.’
• 1 = ’/’
• 2–11 = ’0’ to ’9’
• 12–37 = ’A’ to ’Z’
• 38–63 = ’a’ to ’z’

When the remaining bits are zero or all bits have been translated, a null terminator is appended to the string. An input value of 0 results in the empty string.

The a64l function performs the reverse translation. Each character is used to generate a 6-bit value for up to 30 bits and then a 2-bit value to complete a 32-bit result. The null terminator means that the remaining digits are 0. An empty input string or NULL string results in 0L. An invalid string results in undefined behavior. If the size of a long is greater than 32 bits, the result is sign-extended.

Returns
l64a returns a null-terminated string of 0 to 6 characters. a64l returns the 32-bit translated value from the input character string.

Portability
l64a and a64l are non-ANSI and are defined by the Single Unix Specification.

Supporting OS subroutines required: None.