Find Fortran file used in R package

While trying to figure out how the Leaps package works, I came across this command:

qrleaps <- .Fortran("makeqr", np = as.integer(np), nn = as.integer(nn), 
wt = as.double(wt), tx = t(xx), y = as.double(y), d = numeric(np), 
rbar = numeric(nrbar), thetab = numeric(np), sserr = numeric(1), 
ier = as.integer(0), PACKAGE = "leaps")

I understand that it uses a Fortran subroutine called makeqr. I would like to locate this file and read its source code. Any ideas?

>Solution :

My approach is as follows:

1. Google "leaps CRAN GitHub" to find the GitHub source clone
2. the src/ directory: https://github.com/cran/leaps/tree/master/src
3. Ctrl+f there or use the repo search feature in GitHub. or in extreme cases, clone the repo and use command-line grep to find the code I need.