I looked at this and decided to do -5 * -4 in binary.

[Evan]

I messed up.
http://fourier.eng.hmc.edu/e85_old/lectures/arithmetic_html/node9.html


I messed up again.

I think it is:
111011
111100
_______
     000000
    000000
   111011
  111011
111011
111011
_______

Code Select Expand

1111 0111100100


I read my code
left to right
first I count the ones
second I count the zeros
third I count the ones' segments
forth I count the zeros' segments

.

Please let me know why I am wrong.

My programmer calculator says -5 * -4 is -1. Weird.


Due to my calculator I think I need to take 15864 - (my code) to correct the result.

[gelatine1]

Do 4*5 instead and then take 2's complement. The thing marked in yellow should be your result. EDIT: don't take 2's complement...
For binary multiplications I.
would suggest this algorithm http://en.wikipedia.org/wiki/Multiplication_algorithm#Peasant_or_binary_multiplication
In fact it is just the same as long multiplication though.

[Evan]

Do 4*5 instead and then take 2's complement. The thing marked in yellow should be your result. EDIT: don't take 2's complement...
For binary multiplications I.
would suggest this algorithm http://en.wikipedia.org/wiki/Multiplication_algorithm#Peasant_or_binary_multiplication
In fact it is just the same as long multiplication though.

In my system's calculator the number I found for -20 doesn't matter after many ghost errors. What you showed me I do not understand.

[Evan]

Should we explain long multiplication to each other on smaller number scales?
Should we use the decimal point in our long multiplication?


Please move this to the romper.