Multiplication by Halving and Doubling in AARCH64 Assembly

While multiplication is defined in the context of repeated addition, implementing it that way algorithmically is not nearly as efficient as some other approaches. One algorithm for multiplication that is an order of magnitude faster is to halve one number while doubling the other. I gave myself the challenge of implementing this algorithm in AARCH64 Assembly, and it was not too hard.

Continue reading

Understanding the MIXAL insertion sort.

A debugger is a wonderful tool for understanding what actually happens in a piece of code. Donald Knuth’s coding in TAOCP is archaic enough that I do not understand it just by reading through. This is due to a combination of my unfamiliarity with MIXAL, as well as some of the coding conventions he’s chosen. So, I’m going to step through the MIXAL code in mixvm, and annotate what I find.

Continue reading

A Horrible Conversion from Binary to Decimal in (ARM64) Assembly

This is not my finest code. It is the worst case of “just make it work” I’ve produced all week.

But it runs.

What does it do? It takes the first binary number in an array, and converts it to decimal. It assumes that the number is no more than 3 digits long.

It divides that number by 100 to get the 100s digit. Then it multiples that number by 100, assuming that it has gotten truncated. It subtracts that value from the original number to chop off the 100s digit, and divides the result by 10 to get the 10s digit.

Continue reading