From 53bbf4bf23877fcf56281bdd706b4cc7ed0413ce Mon Sep 17 00:00:00 2001
From: Joe Taylor <joe@princeton.edu>
Date: Mon, 2 Jan 2023 13:21:42 -0500
Subject: [PATCH] Protect against possible bounds error in q65_sync.f90.

---
 q65w/libq65/q65_sync.f90 | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/q65w/libq65/q65_sync.f90 b/q65w/libq65/q65_sync.f90
index 6fb5b3e03..06caffd74 100644
--- a/q65w/libq65/q65_sync.f90
+++ b/q65w/libq65/q65_sync.f90
@@ -25,12 +25,14 @@ subroutine q65_sync(ss,i0,nts_q65,sync_ok,snr,xdt)
   endif
 
   m=nts_q65/2
+  i1=max(1,i0-m)
+  i2=min(NFFT,i0+m)
   ccf=0.
   do lag=0,LAGMAX                     !Search over range of DT
      do j=1,22                        !Test for Q65 sync
         k=isync(j) + lag
-        ccf(lag)=ccf(lag) + sum(ss(k,i0-m:i0+m)) + sum(ss(k+1,i0-m:i0+m)) &
-             + sum(ss(k+2,i0-m:i0+m))
+        ccf(lag)=ccf(lag) + sum(ss(k,i1:i2)) + sum(ss(k+1,i1:i2)) &
+             + sum(ss(k+2,i1:i2))
 ! Q: Should we use weighted sums, perhaps a Lorentzian peak?
      enddo
   enddo