if not modules then modules = { } end modules ['util-sac'] = {
    version   = 1.001,
    comment   = "companion to luat-lib.mkiv",
    author    = "Hans Hagen, PRAGMA-ADE, Hasselt NL",
    copyright = "PRAGMA ADE / ConTeXt Development Team",
    license   = "see context related readme files"
}

-- experimental string access (some 3 times faster than file access when messing
-- with bytes)

local byte, sub = string.byte, string.sub
local extract = bit32 and bit32.extract

utilities         = utilities or { }
local streams     = { }
utilities.streams = streams

function streams.open(filename,zerobased)
    local f = io.loaddata(filename)
    return { f, 1, #f, zerobased or false }
end

function streams.close()
    -- dummy
end

function streams.size(f)
    return f and f[3] or 0
end

function streams.setposition(f,i)
    if f[4] then
        -- zerobased
        if i <= 0 then
            f[2] = 1
        else
            f[2] = i + 1
        end
    else
        if i <= 1 then
            f[2] = 1
        else
            f[2] = i
        end
    end
end

function streams.getposition(f)
    if f[4] then
        -- zerobased
        return f[2] - 1
    else
        return f[2]
    end
end

function streams.look(f,n,chars)
    local b = f[2]
    local e = b + n - 1
    if chars then
        return sub(f[1],b,e)
    else
        return byte(f[1],b,e)
    end
end

function streams.skip(f,n)
    f[2] = f[2] + n
end

function streams.readbyte(f)
    local i = f[2]
    f[2] = i + 1
    return byte(f[1],i)
end

function streams.readbytes(f,n)
    local i = f[2]
    local j = i + n
    f[2] = j
    return byte(f[1],i,j-1)
end

function streams.readbytetable(f,n)
    local i = f[2]
    local j = i + n
    f[2] = j
    return { byte(f[1],i,j-1) }
end

function streams.skipbytes(f,n)
    f[2] = f[2] + n
end

function streams.readchar(f)
    local i = f[2]
    f[2] = i + 1
    return sub(f[1],i,i)
end

function streams.readstring(f,n)
    local i = f[2]
    local j = i + n
    f[2] = j
    return sub(f[1],i,j-1)
end

function streams.readinteger1(f)  -- one byte
    local i = f[2]
    f[2] = i + 1
    local n = byte(f[1],i)
    if n  >= 0x80 then
        return n - 0x100
    else
        return n
    end
end

streams.readcardinal1 = streams.readbyte  -- one byte
streams.readcardinal  = streams.readcardinal1
streams.readinteger   = streams.readinteger1

function streams.readcardinal2(f)
    local i = f[2]
    local j = i + 1
    f[2] = j + 1
    local a, b = byte(f[1],i,j)
    return 0x100 * a + b
end

function streams.readcardinal2LE(f)
    local i = f[2]
    local j = i + 1
    f[2] = j + 1
    local b, a = byte(f[1],i,j)
    return 0x100 * a + b
end

function streams.readinteger2(f)
    local i = f[2]
    local j = i + 1
    f[2] = j + 1
    local a, b = byte(f[1],i,j)
    if a >= 0x80 then
        return 0x100 * a + b - 0x10000
    else
        return 0x100 * a + b
    end
end

function streams.readinteger2le(f)
    local i = f[2]
    local j = i + 1
    f[2] = j + 1
    local b, a = byte(f[1],i,j)
    if a >= 0x80 then
        return 0x100 * a + b - 0x10000
    else
        return 0x100 * a + b
    end
end

function streams.readcardinal3(f)
    local i = f[2]
    local j = i + 2
    f[2] = j + 1
    local a, b, c = byte(f[1],i,j)
    return 0x10000 * a + 0x100 * b + c
end

function streams.readcardinal3le(f)
    local i = f[2]
    local j = i + 2
    f[2] = j + 1
    local c, b, a = byte(f[1],i,j)
    return 0x10000 * a + 0x100 * b + c
end

function streams.readinteger3(f)
    local i = f[2]
    local j = i + 3
    f[2] = j + 1
    local a, b, c = byte(f[1],i,j)
    if a >= 0x80 then
        return 0x10000 * a + 0x100 * b + c - 0x1000000
    else
        return 0x10000 * a + 0x100 * b + c
    end
end

function streams.readinteger3le(f)
    local i = f[2]
    local j = i + 3
    f[2] = j + 1
    local c, b, a = byte(f[1],i,j)
    if a >= 0x80 then
        return 0x10000 * a + 0x100 * b + c - 0x1000000
    else
        return 0x10000 * a + 0x100 * b + c
    end
end

function streams.readcardinal4(f)
    local i = f[2]
    local j = i + 3
    f[2] = j + 1
    local a, b, c, d = byte(f[1],i,j)
    return 0x1000000 * a + 0x10000 * b + 0x100 * c + d
end

function streams.readinteger4(f)
    local i = f[2]
    local j = i + 3
    f[2] = j + 1
    local a, b, c, d = byte(f[1],i,j)
    if a >= 0x80 then
        return 0x1000000 * a + 0x10000 * b + 0x100 * c + d - 0x100000000
    else
        return 0x1000000 * a + 0x10000 * b + 0x100 * c + d
    end
end

function streams.readinteger4le(f)
    local i = f[2]
    local j = i + 3
    f[2] = j + 1
    local d, c, b, a = byte(f[1],i,j)
    if a >= 0x80 then
        return 0x1000000 * a + 0x10000 * b + 0x100 * c + d - 0x100000000
    else
        return 0x1000000 * a + 0x10000 * b + 0x100 * c + d
    end
end

function streams.readfixed4(f)
    local i = f[2]
    local j = i + 3
    f[2] = j + 1
    local a, b, c, d = byte(f[1],i,j)
    if a >= 0x80 then
        return (0x100 * a + b - 0x10000) + (0x100 * c + d)/0x10000
    else
        return (0x100 * a + b          ) + (0x100 * c + d)/0x10000
    end
end

function streams.readfixed2(f)
    local i = f[2]
    local j = i + 1
    f[2] = j + 1
    local a, b = byte(f[1],i,j)
    if a >= 0x80 then
        return (a - 0x100) + b/0x100
    else
        return (a        ) + b/0x100
    end
end

if extract then

    local extract = bit32.extract
    local band    = bit32.band

    function streams.read2dot14(f)
        local i = f[2]
        local j = i + 1
        f[2] = j + 1
        local a, b = byte(f[1],i,j)
        if a >= 0x80 then
            local n = -(0x100 * a + b)
            return - (extract(n,14,2) + (band(n,0x3FFF) / 16384.0))
        else
            local n =   0x100 * a + b
            return   (extract(n,14,2) + (band(n,0x3FFF) / 16384.0))
        end
    end

end

function streams.skipshort(f,n)
    f[2] = f[2] + 2*(n or 1)
end

function streams.skiplong(f,n)
    f[2] = f[2] + 4*(n or 1)
end

if sio and sio.readcardinal2 then

    local readcardinal1  = sio.readcardinal1
    local readcardinal2  = sio.readcardinal2
    local readcardinal3  = sio.readcardinal3
    local readcardinal4  = sio.readcardinal4
    local readinteger1   = sio.readinteger1
    local readinteger2   = sio.readinteger2
    local readinteger3   = sio.readinteger3
    local readinteger4   = sio.readinteger4
    local readfixed2     = sio.readfixed2
    local readfixed4     = sio.readfixed4
    local read2dot14     = sio.read2dot14
    local readbytes      = sio.readbytes
    local readbytetable  = sio.readbytetable

    function streams.readcardinal1(f)
        local i = f[2]
        f[2] = i + 1
        return readcardinal1(f[1],i)
    end
    function streams.readcardinal2(f)
        local i = f[2]
        f[2] = i + 2
        return readcardinal2(f[1],i)
    end
    function streams.readcardinal3(f)
        local i = f[2]
        f[2] = i + 3
        return readcardinal3(f[1],i)
    end
    function streams.readcardinal4(f)
        local i = f[2]
        f[2] = i + 4
        return readcardinal4(f[1],i)
    end
    function streams.readinteger1(f)
        local i = f[2]
        f[2] = i + 1
        return readinteger1(f[1],i)
    end
    function streams.readinteger2(f)
        local i = f[2]
        f[2] = i + 2
        return readinteger2(f[1],i)
    end
    function streams.readinteger3(f)
        local i = f[2]
        f[2] = i + 3
        return readinteger3(f[1],i)
    end
    function streams.readinteger4(f)
        local i = f[2]
        f[2] = i + 4
        return readinteger4(f[1],i)
    end
 -- function streams.readfixed2(f) -- needs recent luatex
 --     local i = f[2]
 --     f[2] = i + 2
 --     return readfixed2(f[1],i)
 -- end
 -- function streams.readfixed4(f) -- needs recent luatex
 --     local i = f[2]
 --     f[2] = i + 4
 --     return readfixed4(f[1],i)
 -- end
    function streams.read2dot4(f)
        local i = f[2]
        f[2] = i + 2
        return read2dot4(f[1],i)
    end
    function streams.readbytes(f,n)
        local i = f[2]
        local s = f[3]
        local p = i + n
        if p > s then
            f[2] = s + 1
        else
            f[2] = p
        end
        return readbytes(f[1],i,n)
    end
    function streams.readbytetable(f,n)
        local i = f[2]
        local s = f[3]
        local p = i + n
        if p > s then
            f[2] = s + 1
        else
            f[2] = p
        end
        return readbytetable(f[1],i,n)
    end

    streams.readbyte       = streams.readcardinal1
    streams.readsignedbyte = streams.readinteger1
    streams.readcardinal   = streams.readcardinal1
    streams.readinteger    = streams.readinteger1

end