From 967c97bb59dfa37d4423684c7357e660ad1e3bbf Mon Sep 17 00:00:00 2001
From: Maria Matejka <mq@ucw.cz>
Date: Tue, 12 Mar 2024 21:08:29 +0100
Subject: [PATCH] Bitops: bitflip function

to flip order of bits in 32b numbers
---
 lib/bitops.c      | 18 ++++++++++++++++++
 lib/bitops.h      |  2 ++
 lib/bitops_test.c | 26 ++++++++++++++++++++++++++
 3 files changed, 46 insertions(+)

diff --git a/lib/bitops.c b/lib/bitops.c
index efb8710e..4b6fee4a 100644
--- a/lib/bitops.c
+++ b/lib/bitops.c
@@ -68,3 +68,21 @@ u32_log2(u32 v)
   return r;
 }
 
+
+/**
+ * u32_bitflip - flips bits in number.
+ * @n: number
+ *
+ * This function flips bits in the given number such that MSB becomes LSB and vice versa.
+ */
+
+u32
+u32_bitflip(u32 n)
+{
+  n = ((n & 0xffff0000) >> 16) | ((n & 0x0000ffff) << 16);
+  n = ((n & 0xff00ff00) >> 8) | ((n & 0x00ff00ff) << 8);
+  n = ((n & 0xf0f0f0f0) >> 4) | ((n & 0x0f0f0f0f) << 4);
+  n = ((n & 0xcccccccc) >> 2) | ((n & 0x33333333) << 2);
+  n = ((n & 0xaaaaaaaa) >> 1) | ((n & 0x55555555) << 1);
+  return n;
+}
diff --git a/lib/bitops.h b/lib/bitops.h
index 0beda2a3..1db89f0b 100644
--- a/lib/bitops.h
+++ b/lib/bitops.h
@@ -25,6 +25,8 @@ uint u32_masklen(u32 x);
 
 u32 u32_log2(u32 v);
 
+u32 u32_bitflip(u32 n);
+
 static inline u32 u32_hash(u32 v) { return v * 2902958171u; }
 
 static inline u8 u32_popcount(u32 v) { return __builtin_popcount(v); }
diff --git a/lib/bitops_test.c b/lib/bitops_test.c
index f816b9d1..db2bdc03 100644
--- a/lib/bitops_test.c
+++ b/lib/bitops_test.c
@@ -110,6 +110,31 @@ t_log2(void)
   return 1;
 }
 
+static void
+check_bitflip(u32 n)
+{
+  u32 rot = u32_bitflip(n);
+  for (int i = 0; i < 16; i++)
+  {
+    bt_assert(!((n >> i) & 1) == !((rot << i) & 0x80000000));
+    bt_assert(!((rot >> i) & 1) == !((n << i) & 0x80000000));
+  }
+}
+
+static int
+t_bitflip(void)
+{
+  u32 i;
+
+  for (i = 0; i < MAX_NUM; i++)
+  {
+    check_bitflip(i);
+    check_bitflip((u32) bt_random());
+  }
+
+  return 1;
+}
+
 int
 main(int argc, char *argv[])
 {
@@ -118,6 +143,7 @@ main(int argc, char *argv[])
   bt_test_suite(t_mkmask, "u32_mkmask()");
   bt_test_suite(t_masklen, "u32_masklen()");
   bt_test_suite(t_log2, "u32_log2()");
+  bt_test_suite(t_bitflip, "u32_bitflip()");
 
   return bt_exit_value();
 }