Processing Time of Multiplicatoin and Addition

We know that the processing of a multiplication is by far greater than that of addition.

I did this test.

For testing the requeired clock cycles for an addition I wrote the following program.

clc

clear

N = 10^8;

tic for i=1:N j=i+i; end processing_time = toc;

av_time = processing_time/N;

clk_period = 1/(3.4*10^9); % computer clock period time = 1/f where f = 3.4 GHz

av_time2clk_period = av_time/clk_period

Then I changed j= i+i ; to j = i*i to see how many cycles a multiplication takes time. Amazingly both addition and multiplication result in the same processing time. Why?

Answer 1

[Bill Winter]

There's a really good explanation of this over at stackoverflow:

http://stackoverflow.com/questions/1146455/whats-the-relative-speed-of-floating-point-add-vs-floating-point-multiply