It's a set of routines for arithmetic on real numbers. The microprocessor here (the 6502, as used in the Apple I and II) could only operate on bytes, that, is whole numbers between 0 and 255. Even worse, it could only add and subtract them. But with this library you could compute 1.2627 - 1099.56, or even the square root of pi. Amazingly, Wozniac fit the basic functions (add, subtract, multiply and divide) into 239 bytes, using just 127 instructions total.That's some pretty impressive coding, and having read through it a few times, it's ingenious. For example both the multiply and divide routines loop 23 times, once for each bit in the result. Does Woz waste two bytes by writing the constant 23 in both places? Of course not! He loads the constant 23 in a prefix routine that both share:As another example, the algorithms need to take the absolute value of M1 and M2. You might write