From e554b4e06814101b6a68ca39b93b324c9fd55491 Mon Sep 17 00:00:00 2001
From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Tue, 21 Jun 2022 11:34:38 +0100
Subject: [PATCH] reduce without MVs

---
 openpower/sv/preduce.py | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/openpower/sv/preduce.py b/openpower/sv/preduce.py
index 242b3ab6b..815def6b7 100644
--- a/openpower/sv/preduce.py
+++ b/openpower/sv/preduce.py
@@ -1,8 +1,10 @@
 from copy import copy
 
 def preduce(vl, vec, pred):
+    vec = copy(vec) # must not damage predicate
     pred = copy(pred) # must not damage predicate
     step = 1
+    print(" start", step, pred, vec)
     while step < vl:
         step *= 2
         for i in range(0, vl, step):
@@ -14,12 +16,35 @@ def preduce(vl, vec, pred):
                 vec[i] = vec[other]
             pred[i] |= other_pred
         print("   row", step, pred, vec)
+    return vec
+
+def preducei(vl, vec, pred):
+    pred = copy(pred) # must not damage predicate
+    step = 1
+    ix = list(range(vl))
+    print(" start", step, pred, vec)
+    while step < vl:
+        step *= 2
+        for i in range(0, vl, step):
+            other = i + step // 2
+            ci = ix[i]
+            oi = ix[other] if other < vl else None
+            other_pred = other < vl and pred[oi]
+            if pred[ci] and other_pred:
+                vec[ci] += vec[oi]
+            elif other_pred:
+                ix[i] = oi
+            pred[ci] |= other_pred
+        print("   row", step, pred, vec, ix)
 
 if __name__ == '__main__':
     vec = [1, 2, 3, 4, 9, 5, 6]
-    prd = [1, 1, 1, 1, 0, 1, 1]
+    prd = [0, 1, 1, 1, 0, 0, 1]
     print (vec)
-    preduce(len(vec), vec, prd)
+    res = preduce(len(vec), vec, prd)
+    print (res)
+    preducei(len(vec), vec, prd)
     print (vec)
     print ()
+    assert vec == res
 
-- 
2.30.2