Re: Speed over beauty - vstruct vs struct

[Xavier Wang <weasley.wx@...>]

If you want a C implement, you can try my lbuffer[1], it's a mutable
string implement of Lua. it has a pack/unpack interface.

some examples (from README.rst):

-- read *.mo file
function read_mofile(b)
    local info = b:unpack [[ {
        magic = i,
        revision = i,
        nstrings = i,
        orig_tab_offset = i,
        trans_tab_offset = i,
        hash_tab_size = i,
        hash_tab_offset = i,
    } ]]

    local trans = {}
    for i = 0, info.nstrings-1 do
        local o_len, o_offset = b:unpack(info.orig_tab_offset+8*i+1, "<ii")
        local t_len, t_offset = b:unpack(info.trans_tab_offset+8*i+1, "<ii")
        local os = b:unpack(o_offset+1, "s")
        local ts = b:unpack(t_offset+1, "s")
        trans[os] = ts
    end
    return info, trans
end


[1]: https://github.com/starwing/lbuffer

2014-07-23 20:21 GMT+08:00 David Crayford <dcrayford@gmail.com>:
> I've recently been investigating Lua structure packing libraries. vstruct is
> a thing of beauty as it allows me to layout a format string that looks like
> a structure,
> and it supports names, tables etc. The downside is that compared to struct
> it's very slow. struct is orders of magnitude faster but it's interface is
> not so nice. It brings
> me to tears to choose a library for speed over beauty but performance is
> important to my project.
>
> How easy would it be to rewrite certain parts of vstruct in C or maybe even
> front end struct with the same semantics as vstruct? The format string below
> is what
> I've knocked up for vstruct.
>
> local fmtstr =
> [[
>   request:  s4
>   key:{
>     department: s1
>     employee_no: s5
>   }
>   name: s20
>   addr1: s20
>   addr2: s20
>   addr3: s20
>   phone_no: s8
>   timestamp: s8
>   salary: s8
>   start_date: s8
>   remarks: s32
>   msg: s60
>   upd_ind: {
>     name: s1
>     addr1: s1
>     addr2: s1
>     addr3: s1
>     phone_no: s1
>     salary: s1
>     start_date: s1
>     remarks: s1
>   }
>   browseeq: s8
>   update_ind: s1
>   delete_ind: s1
>   add_ind: s1
>   error_ind: s1
>   browse_ind: s1
>   dept_ind: s1
>   count: s2
>   total: s2
>   item_no: s2
>   sbtot: s2
>   sbnum: s2
>   lineout: { 10 * {
>     filler1: s6
>     employee_no: s5
>     filler2: s3
>     employee_name: s20
>     filler3: s3
>     employee_phone: s8
>     filler4: s34
>   }}
> ]]
>
>
>
>



-- 
regards,
Xavier Wang.