From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Mon, 7 Mar 2022 22:11:09 +0000 (+0000)
Subject: code-comments
X-Git-Tag: opf_rfc_ls005_v1~3125
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=c4b1cd5cc5d321d7c918ae42de085081984ef088;p=libreriscv.git

code-comments
---

diff --git a/openpower/sv/gf2.py b/openpower/sv/gf2.py
index a07ebf6e1..6798cd1f6 100644
--- a/openpower/sv/gf2.py
+++ b/openpower/sv/gf2.py
@@ -83,21 +83,22 @@ def gf_invert(a) :
     j = 0
 
     for i in range(1, 2*degree+1):
-        if r & mask1:
-            if s & mask1:
+        # could use count-trailing-1s here to skip ahead
+        if r & mask1:          # test MSB of r
+            if s & mask1:      # test MSB of s
                 s ^= r
                 v ^= u
-            s <<= 1 # shift left 1
+            s <<= 1            # shift left 1
             if j == 0:
-                r, s = s, r # swap r,s
+                r, s = s, r    # swap r,s
                 u, v = v<<1, u # shift v and swap
                 j = 1
             else:
-                u >>= 1 # right shift left
+                u >>= 1        # right shift left
                 j -= 1
         else:
-            r <<= 1 # shift left 1
-            u <<= 1 # shift left 1
+            r <<= 1            # shift left 1
+            u <<= 1            # shift left 1
             j += 1
 
     return u