--- -- Bit manipulation library. -- -- @author Patrick Donnelly -- @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 `a` arithmetically right-shifted by `b` -- 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 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