That's the correct formula for adjusting film speed, but use the following to adjust exposure time:
corrected exposure time in seconds = (t+1)^(1/p)-1
where t is the metered exposure time in seconds and p is the Schwarzschild exponent. I should probably also state clearly that the metered exposure time in this formula is at the declared film speed 'd', not at the relative film speed from your Schwarzschild formula.
the equation is correct,but how do you know the value for p?
use this table for tmax100,and note that measured 4 min turn into 40 minutes!
I've answered in a .pdf format to preserve the table.
Hope this helps.
Also included a chart for metered times up to 120 seconds, which is of course extrapolating from Fuji's data.
I believe all the math to be correct, but can't vouch for the accuracy of Fuji's data, and I haven't included the density of the filtration Fuji suggests. As always, test for your own conditions and adjust.