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comparison spec/util_strbitop_spec.lua @ 13429:6cdc6923d65a

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util.strbitop: Add common_prefix_bits() method This returns the number of bits that two strings have in common. It is significantly more efficient than similar calculations in Lua.
author Matthew Wild <mwild1@gmail.com>
date Fri, 23 Feb 2024 12:08:37 +0000
parents 9677df320992
children 1a5e3cf037f6
comparison
equal deleted inserted replaced
13428:dc1ad5f3f597 13429:6cdc6923d65a
36 end); 36 end);
37 it("returns initial string if key is empty", function () 37 it("returns initial string if key is empty", function ()
38 assert.equal("hello", strbitop.sxor("hello", "")); 38 assert.equal("hello", strbitop.sxor("hello", ""));
39 end); 39 end);
40 end); 40 end);
41
42 describe("common_prefix_bits()", function ()
43 local function B(s)
44 assert(#s%8==0, "Invalid test input: B(s): s should be a multiple of 8 bits in length");
45 local byte = 0;
46 local out_str = {};
47 for i = 1, #s do
48 local bit_ascii = s:byte(i);
49 if bit_ascii == 49 then -- '1'
50 byte = byte + 2^((7-(i-1))%8);
51 elseif bit_ascii ~= 48 then
52 error("Invalid test input: B(s): s should contain only '0' or '1' characters");
53 end
54 if (i-1)%8 == 7 then
55 table.insert(out_str, string.char(byte));
56 byte = 0;
57 end
58 end
59 return table.concat(out_str);
60 end
61
62 local _cpb = strbitop.common_prefix_bits;
63 local function test(a, b)
64 local Ba, Bb = B(a), B(b);
65 local ret1 = _cpb(Ba, Bb);
66 local ret2 = _cpb(Bb, Ba);
67 assert(ret1 == ret2, ("parameter order should not make a difference to the result (%s, %s) = %d, reversed = %d"):format(a, b, ret1, ret2));
68 return ret1;
69 end
70 local hex = require "util.hex";
71 it("works on single bytes", function ()
72 assert.equal(0, test("00000000", "11111111"));
73 assert.equal(1, test("10000000", "11111111"));
74 assert.equal(0, test("01000000", "11111111"));
75 assert.equal(0, test("01000000", "11111111"));
76 assert.equal(8, test("11111111", "11111111"));
77 end);
78
79 it("works on multiple bytes", function ()
80 for i = 0, 16 do
81 assert.equal(i, test(string.rep("1", i)..string.rep("0", 16-i), "1111111111111111"));
82 end
83 end);
84 end);
41 end); 85 end);