From 3434faf84addb98ab8d5539c2a38e08fb8ab608a Mon Sep 17 00:00:00 2001
From: Joe Taylor <joe@princeton.edu>
Date: Wed, 31 Jan 2024 14:02:33 -0500
Subject: [PATCH] Check for hard symbol errors.

---
 lib/superfox/hard_symbols.f90 | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 lib/superfox/hard_symbols.f90

diff --git a/lib/superfox/hard_symbols.f90 b/lib/superfox/hard_symbols.f90
new file mode 100644
index 000000000..e97e635dc
--- /dev/null
+++ b/lib/superfox/hard_symbols.f90
@@ -0,0 +1,32 @@
+subroutine hard_symbols(crcvd,f,t,jdat)
+
+  include "sfox_params.f90"
+  complex crcvd(NMAX)                    !Signal as received
+  complex c(0:NSPS-1)                    !Work array, one symbol long
+  real s(0:NSPS-1)                       !Power spectrum
+  integer*1 jdat(ND)                     !Recovered hard-decision symbols
+  integer ipk(1)
+
+  i0=nint(12000.0*t)
+  df=12000.0/NSPS
+  j0=nint(f/df)-128
+  do n=1,ND                             !Loop over all symbols
+     ib=n*NSPS + i0
+     if(n.gt.ND1) ib=(NS+n)*NSPS + i0
+     ia=ib-NSPS+1
+     c=crcvd(ia:ib)
+     call four2a(c,NSPS,1,-1,1)          !Compute symbol spectrum
+     do i=0,NSPS-1
+        s(i)=real(c(i))**2 + aimag(c(i))**2
+     enddo
+     ipk=maxloc(s)
+     ipk(1)=ipk(1)-j0
+     if(ipk(1).ge.64) then
+        jdat(n)=ipk(1)-64
+     else
+        jdat(n)=ipk(1)+256-64
+     endif
+  enddo
+
+  return
+end subroutine hard_symbols