From efc946018bf3a368d82500c36407a7f4cce7c37b Mon Sep 17 00:00:00 2001
From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Sun, 13 Mar 2022 15:26:14 +0000
Subject: [PATCH] add grevlut.py demo code

---
 openpower/sv/grevlut.py | 71 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)
 create mode 100644 openpower/sv/grevlut.py

diff --git a/openpower/sv/grevlut.py b/openpower/sv/grevlut.py
new file mode 100644
index 000000000..3c4cd9279
--- /dev/null
+++ b/openpower/sv/grevlut.py
@@ -0,0 +1,71 @@
+def lut2(imm, a, b):
+    idx = b << 1 | a
+    return (imm>>idx) & 1
+
+def dorow(imm8, step_i, chunk_size):
+    step_o = 0
+    for j in range(64):
+        if (j&chunk_size) == 0:
+           imm = (imm8 & 0b1111)
+        else:
+           imm = (imm8>>4)
+        a = (step_i>>j)&1
+        b = (step_i>>(j ^ chunk_size))&1
+        res = lut2(imm, a, b)
+        #print(j, bin(imm), a, b, res)
+        step_o |= (res<<j)
+    #print ("  ", chunk_size, bin(step_o))
+    return step_o
+
+def grevlut64(RA, RB, imm, iv):
+    x = RA
+    if (iv): x = ~x;
+    shamt = RB & 63;
+    #print (bin(shamt), bin(63))
+    for i in range(6):
+        step = 1<<i
+        if (shamt & step):
+            x = dorow(imm, x, step)
+    return x & ((1<<64)-1)
+
+
+if __name__ == '__main__':
+    # answer: 8888888...
+    RA = 0x5555555555555555
+    RB = 0b0010
+    imm = 0b11000110
+    x = grevlut64(RA, RB, imm, 1)
+    print ("grevlut", hex(RA), bin(RB), bin(imm), hex(x), "\n", bin(x))
+
+    # answer: 80808080...
+    RB = 0b00110
+    imm = 0b11000110
+    x = grevlut64(RA, RB, imm, 1)
+    print ("grevlut", hex(RA), bin(RB), bin(imm), hex(x), "\n", bin(x))
+
+    # answer: 80008000...
+    RB = 0b01110
+    imm = 0b11000110
+    x = grevlut64(RA, RB, imm, 1)
+    print ("grevlut", hex(RA), bin(RB), bin(imm), hex(x), "\n", bin(x))
+    print()
+
+    # answer: 01010101...
+    RB = 0b00110
+    imm = 0b01101100
+    x = grevlut64(RA, RB, imm, 0)
+    print ("grevlut", hex(RA), bin(RB), bin(imm), hex(x), "\n", bin(x))
+
+    # answer: 00010001...
+    RB = 0b01110
+    imm = 0b01101100
+    x = grevlut64(RA, RB, imm, 0)
+    print ("grevlut", hex(RA), bin(RB), bin(imm), hex(x), "\n", bin(x))
+    print()
+
+    for RB in range(64):
+        RA = 0x5555555555555555
+        imm = 0b11000110
+        x = grevlut64(RA, RB, imm, 1)
+        print ("grevlut", hex(RA), bin(RB), bin(imm), hex(x), "\n", bin(x))
+        # answer: 8888888...
-- 
2.30.2