From: Jacob Lifshay <programmerjake@gmail.com>
Date: Tue, 18 Jan 2022 04:57:03 +0000 (-0800)
Subject: add log2 pseudo-code helper
X-Git-Tag: sv_maxu_works-initial~553
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=4386dd8bb2d41db227263a947bface79d5acaf0c;p=openpower-isa.git

add log2 pseudo-code helper
---

diff --git a/src/openpower/decoder/helpers.py b/src/openpower/decoder/helpers.py
index e37d4777..3dba5567 100644
--- a/src/openpower/decoder/helpers.py
+++ b/src/openpower/decoder/helpers.py
@@ -360,6 +360,15 @@ def bitrev(val, VL):
     return result
 
 
+def log2(val):
+    """return the base-2 logarithm of `val`. Only works for powers of 2."""
+    if isinstance(val, SelectableInt):
+        val = val.value
+    retval = val.bit_length() - 1
+    assert val == 2 ** retval, "value is not a power of 2"
+    return retval
+
+
 # For these tests I tried to find power instructions that would let me
 # isolate each of these helper operations. So for instance, when I was
 # testing the MASK() function, I chose rlwinm and rldicl because if I