From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Wed, 23 Jun 2021 15:23:56 +0000 (+0100)
Subject: add bitrev function to be used in LD-ST-bitrev FFT/DCT
X-Git-Tag: xlen-bcd~412
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=e84559bed6550abc8b336969882a6312ba971368;p=openpower-isa.git

add bitrev function to be used in LD-ST-bitrev FFT/DCT
---

diff --git a/src/openpower/decoder/helpers.py b/src/openpower/decoder/helpers.py
index 6b270a96..ed8679d6 100644
--- a/src/openpower/decoder/helpers.py
+++ b/src/openpower/decoder/helpers.py
@@ -364,6 +364,19 @@ def FPDIV64(FRA, FRB, sign=1):
     return cvt
 
 
+
+def bitrev(val, VL):
+    """Returns the integer whose value is the reverse of the lowest
+    'width' bits of the integer 'val'
+    """
+	result = 0
+    width = VL.bit_length()
+	for _ in range(width):
+		result = (result << 1) | (val & 1)
+		val >>= 1
+	return result
+
+
 # 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