From d217a6b9f1d897aef2375e3cfb9ef7fbc780733b Mon Sep 17 00:00:00 2001
From: Anthony Scemama <scemama@irsamc.ups-tlse.fr>
Date: Fri, 26 Mar 2021 00:26:31 +0100
Subject: [PATCH] Optimized get_all_spin_singles

---
 src/determinants/spindeterminants.irp.f | 46 +++++++++----------------
 1 file changed, 16 insertions(+), 30 deletions(-)

diff --git a/src/determinants/spindeterminants.irp.f b/src/determinants/spindeterminants.irp.f
index 8ba405e0..765ee394 100644
--- a/src/determinants/spindeterminants.irp.f
+++ b/src/determinants/spindeterminants.irp.f
@@ -1193,16 +1193,10 @@ subroutine get_all_spin_singles_and_doubles_$N_int(buffer, idx, spindet, size_bu
       xorvec(k) = xor( spindet(k), buffer(k,i) )
     enddo
 
-    if (xorvec(1) /= 0_8) then
-      degree = popcnt(xorvec(1))
-    else
-      degree = 0
-    endif
+    degree = 0
 
-    do k=2,$N_int
-      if ( (degree <= 4).and.(xorvec(k) /= 0_8) ) then
+    do k=1,$N_int
         degree = degree + popcnt(xorvec(k))
-      endif
     enddo
 
     if ( degree == 4 ) then
@@ -1247,23 +1241,19 @@ subroutine get_all_spin_singles_$N_int(buffer, idx, spindet, size_buffer, single
       xorvec(k) = xor( spindet(k), buffer(k,i) )
     enddo
 
-    if (xorvec(1) /= 0_8) then
-      degree = popcnt(xorvec(1))
-    else
-      degree = 0
-    endif
+    degree = 0
 
-    do k=2,$N_int
-      if ( (degree <= 2).and.(xorvec(k) /= 0_8) ) then
+    do k=1,$N_int
         degree = degree + popcnt(xorvec(k))
-      endif
     enddo
 
-    if ( degree == 2 ) then
-      singles(n_singles) = idx(i)
-      n_singles = n_singles+1
+    if ( degree /= 2 ) then
+      cycle
     endif
 
+    singles(n_singles) = idx(i)
+    n_singles = n_singles+1
+
   enddo
   n_singles = n_singles-1
 
@@ -1296,23 +1286,19 @@ subroutine get_all_spin_doubles_$N_int(buffer, idx, spindet, size_buffer, double
       xorvec(k) = xor( spindet(k), buffer(k,i) )
     enddo
 
-    if (xorvec(1) /= 0_8) then
-      degree = popcnt(xorvec(1))
-    else
-      degree = 0
-    endif
+    degree = 0
 
-    do k=2,$N_int
-      if ( (degree <= 4).and.(xorvec(k) /= 0_8) ) then
+    do k=1,$N_int
         degree = degree + popcnt(xorvec(k))
-      endif
     enddo
 
-    if ( degree == 4 ) then
-      doubles(n_doubles) = idx(i)
-      n_doubles = n_doubles+1
+    if ( degree /= 4 ) then
+      cycle
     endif
 
+    doubles(n_doubles) = idx(i)
+    n_doubles = n_doubles+1
+
   enddo
 
   n_doubles = n_doubles-1