From 344b9c11f325c4bf73c038008163d90484c780d9 Mon Sep 17 00:00:00 2001
From: Joe Taylor <joe@princeton.edu>
Date: Tue, 23 Jun 2020 15:08:56 -0400
Subject: [PATCH] Speed up gen_fst280wave() by nearly x10 for longest FST280
 transmissions.

---
 lib/fst280/gen_fst280wave.f90 | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/lib/fst280/gen_fst280wave.f90 b/lib/fst280/gen_fst280wave.f90
index 9245af406..8485b99d8 100644
--- a/lib/fst280/gen_fst280wave.f90
+++ b/lib/fst280/gen_fst280wave.f90
@@ -1,21 +1,31 @@
 subroutine gen_fst280wave(itone,nsym,nsps,nwave,fsample,hmod,f0,    &
      icmplx,cwave,wave)
 
+  parameter(NTAB=65536)
   real wave(nwave)
-  complex cwave(nwave)
+  complex cwave(nwave),ctab(0:NTAB-1)
   real, allocatable, save :: pulse(:)
   real, allocatable :: dphi(:)
   integer hmod
   integer itone(nsym)
+!  integer*8 count0,count1,clkfreq
   logical first
   data first/.true./
   data nsps0/-99/
-  save first,twopi,dt,tsym,nsps0
+  save first,twopi,dt,tsym,nsps0,ctab
+
+!  call system_clock(count0,clkfreq)
+  if(first) then
+     twopi=8.0*atan(1.0)
+     do i=0,NTAB-1
+        phi=i*twopi/NTAB
+        ctab(i)=cmplx(cos(phi),sin(phi))
+     enddo
+  endif
 
   if(first.or.nsps.ne.nsps0) then
      if(allocated(pulse)) deallocate(pulse)
      allocate(pulse(1:3*nsps))
-     twopi=8.0*atan(1.0)
      dt=1.0/fsample
      tsym=nsps/fsample
 ! Compute the smoothed frequency-deviation pulse
@@ -46,12 +56,15 @@ subroutine gen_fst280wave(itone,nsym,nsps,nwave,fsample,hmod,f0,    &
   k=0
   do j=0,(nsym+2)*nsps-1
      k=k+1
+     i=phi*float(NTAB)/twopi
+     i=iand(i,NTAB-1)
      if(icmplx.eq.0) then
-        wave(k)=sin(phi)
+        wave(k)=real(ctab(i))
      else
-        cwave(k)=cmplx(cos(phi),sin(phi))
+        cwave(k)=ctab(i)
      endif
-     phi=mod(phi+dphi(j),twopi)
+     phi=phi+dphi(j)
+     if(phi.gt.twopi) phi=phi-twopi
   enddo
 
 ! Compute the ramp-up and ramp-down symbols
@@ -73,5 +86,10 @@ subroutine gen_fst280wave(itone,nsym,nsps,nwave,fsample,hmod,f0,    &
           (1.0+cos(twopi*(/(i,i=0,nsps/2-1)/)/real(nsps)))/2.0
   endif
 
+!  call system_clock(count1,clkfreq)
+!  tt=float(count1-count0)/float(clkfreq)
+!  write(*,3001) tt
+!3001 format('Tgen:',f8.3)
+  
   return
 end subroutine gen_fst280wave