Add bitops module

Currently only bit.band is needed.

For LuaJIT: use builtin bit.band
For Lua 5.1, 5.2: use bit.band from luabitop if available
For Lua 5.3, 5.4: use builtin & operator

Author: rolandlo

lua-vips-1.1-10.rockspec

@@ -24,6 +24,7 @@ build = {
    type = "builtin",
    modules = {
        vips = "src/vips.lua",
+       ["vips.bitops"] = "src/vips/bitops.lua",
        ["vips.cdefs"] = "src/vips/cdefs.lua",
        ["vips.verror"] = "src/vips/verror.lua",
        ["vips.version"] = "src/vips/version.lua",

src/vips/bitops.lua

@@ -0,0 +1,21 @@
+local hasbit, bit = pcall(require, "bit")
+local bitops = {}
+
+if hasbit then -- Lua 5.1, 5.2 with luabitop or LuaJIT
+    bitops.band = bit.band
+elseif (_VERSION == "Lua 5.1" or _VERSION == "Lua 5.2") then
+    error("Bit operations missing. Please install 'luabitop'")
+else -- Lua >= 5.3
+    local band, err = load("return function(a, b) return a & b end")
+    if band then
+        local ok
+        ok, bitops.band = pcall(band)
+        if not ok then
+            error("Execution error")
+        end
+    else
+        error("Compilation error" .. err)
+    end
+end
+
+return bitops

src/vips/voperation.lua

@@ -2,16 +2,16 @@
 -- lookup and call operations
 
 local ffi = require "ffi"
-local bit = require "bit"
 
+local bitops = require "vips.bitops"
 local verror = require "vips.verror"
 local version = require "vips.version"
 local log = require "vips.log"
 local gvalue = require "vips.gvalue"
 local vobject = require "vips.vobject"
 local Image = require "vips.Image"
 
-local band = bit.band
+local band = bitops.band
 local type = type
 local error = error
 local pairs = pairs