add FITPACK Fortran library

start developing of FITPACK C++ bindings
mount_server.cpp: fix compilation error with GCC15

cxx/fitpack/fpdisc.f

@@ -0,0 +1,44 @@
+      recursive subroutine fpdisc(t,n,k2,b,nest)
+      implicit none
+c  subroutine fpdisc calculates the discontinuity jumps of the kth
+c  derivative of the b-splines of degree k at the knots t(k+2)..t(n-k-1)
+c  ..scalar arguments..
+      integer n,k2,nest
+c  ..array arguments..
+      real*8 t(n),b(nest,k2)
+c  ..local scalars..
+      real*8 an,fac,prod
+      integer i,ik,j,jk,k,k1,l,lj,lk,lmk,lp,nk1,nrint
+c  ..local array..
+      real*8 h(12)
+c  ..
+      k1 = k2-1
+      k = k1-1
+      nk1 = n-k1
+      nrint = nk1-k
+      an = nrint
+      fac = an/(t(nk1+1)-t(k1))
+      do 40 l=k2,nk1
+        lmk = l-k1
+        do 10 j=1,k1
+          ik = j+k1
+          lj = l+j
+          lk = lj-k2
+          h(j) = t(l)-t(lk)
+          h(ik) = t(l)-t(lj)
+  10    continue
+        lp = lmk
+        do 30 j=1,k2
+          jk = j
+          prod = h(j)
+          do 20 i=1,k
+            jk = jk+1
+            prod = prod*h(jk)*fac
+  20      continue
+          lk = lp+k1
+          b(lmk,j) = (t(lk)-t(lp))/prod
+          lp = lp+1
+  30    continue
+  40  continue
+      return
+      end