1 files changed, 79 insertions, 0 deletions
diff --git a/nselib/bits.lua b/nselib/bits.lua
new file mode 100644
index 0000000..b620168
--- /dev/null
+++ b/nselib/bits.lua
@@ -0,0 +1,79 @@
+---
+-- Bit manipulation library.
+--
+-- @author Patrick Donnelly <batrick@batbytes.com>
+-- @copyright Same as Nmap -- see https://nmap.org/book/man-legal.html
+-- @see https://www.lua.org/manual/5.3/manual.html#3.4.2
+--
+-- @class module
+-- @name bits
+
+local assert = assert
+local error = error
+local unittest = require "unittest"
+
+local _ENV = {}
+
+--- Reverses bits in integer.
+--
+-- @param n The integer.
+-- @param size The bit width of the integer (default: 8).
+-- @return The reversed integer.
+function reverse (n, size)
+    if not size or size == 8 then
+        n = n & 0xff
+        n = (n & 0xf0) >> 4 | (n & 0x0f) << 4
+        n = (n & 0xcc) >> 2 | (n & 0x33) << 2
+        n = (n & 0xaa) >> 1 | (n & 0x55) << 1
+        n = n & 0xff
+    elseif size == 32 then
+        n = n & 0xffffffff
+        n = ((n >> 1) & 0x55555555) | ((n & 0x55555555) << 1);
+        n = ((n >> 2) & 0x33333333) | ((n & 0x33333333) << 2);
+        n = ((n >> 4) & 0x0F0F0F0F) | ((n & 0x0F0F0F0F) << 4);
+        n = ((n >> 8) & 0x00FF00FF) | ((n & 0x00FF00FF) << 8);
+        n = ( n >> 16             ) | ( n               << 16);
+        n = n & 0xffffffff
+    else
+        error("invalid size: "..size)
+    end
+    return n
+end
+
+--- Returns <code>a</code> arithmetically right-shifted by <code>b</code>
+-- places.
+-- @param a Number to perform the shift on.
+-- @param b Number of shifts.
+function arshift(a, b)
+    if a < 0 then
+        if a % 2 == 0 then -- even?
+            return a // (1<<b)
+        else
+            return a // (1<<b) + 1
+        end
+    else
+        return a >> b
+    end
+end
+
+if not unittest.testing() then
+  return _ENV
+end
+
+local equal = unittest.equal
+
+test_suite = unittest.TestSuite:new()
+test_suite:add_test(equal(reverse(0x00, 8), 0x00), "reverse 8-bit number")
+test_suite:add_test(equal(reverse(0x01, 8), 0x80), "reverse 8-bit number")
+test_suite:add_test(equal(reverse(0x80, 8), 0x01), "reverse 8-bit number")
+test_suite:add_test(equal(reverse(0xff, 8), 0xff), "reverse 8-bit number")
+test_suite:add_test(equal(reverse(0x88, 8), 0x11), "reverse 8-bit number")
+test_suite:add_test(equal(reverse(0x5c, 8), 0x3a), "reverse 8-bit number")
+
+test_suite:add_test(equal(reverse(0x00000000, 32), 0x00000000), "reverse 32-bit number")
+test_suite:add_test(equal(reverse(0x00000001, 32), 0x80000000), "reverse 32-bit number")
+test_suite:add_test(equal(reverse(0x80000000, 32), 0x00000001), "reverse 32-bit number")
+test_suite:add_test(equal(reverse(0xffffffff, 32), 0xffffffff), "reverse 32-bit number")
+test_suite:add_test(equal(reverse(0x22221234, 32), 0x2c484444), "reverse 32-bit number")
+
+return _ENV