OpenEuphoria

Re: Pointers

• Posted by "Arthur Adamson (by way of Arthur Adamson <euclid at isoc.net>)" Jan 17, 1999
• 819 views

--        With all the talk of pointers, the following may save someone some
--trouble. Bottom line, in a numerical sequence, the storage space is
--somewhar unpredictable...so forget about pointer arithmetic.
--        A small demo prog follows showing the bytes per term may change
--unexpectdly as the data varies from float to float auto converted to
--integer whae possible.


--Demo for size of a numeric sequence.

--include bytes.e

--This handy bytes.e came from Rob Craig. It estimates the # of bytes needed
--by an object. I have found it useful.

--Bytes.e

global function bytes(object x)
-- estimates the number of bytes of storage needed for any
-- Euphoria 2.0 data object (atom or sequence).
    integer space

    if integer(x) then
       return 4
    elsif atom(x) then
       return 16
    else
       -- sequence
       space = 24 -- overhead
       for i = 1 to length(x) do
           space = space + bytes(x[i])
       end for
       return space
    end if
end function

-->integer int
-->int = 1
--? bytes_needed(1)                    -- 4
--? bytes_needed(1.5)                  -- 16
--? bytes_needed({1,2,3})              -- 36
--? bytes_needed({{1.5,2.5}, {1,2}})   -- 112
--? bytes_needed({{1,2},{}, {},  {1,2}})   -- 88 , 112, 136
--? bytes_needed(int)


--END bytes.e


--Make a seq of floats with howMany elements
sequence seq1
integer howMany

howMany = 10

seq1 = repeat(1.1, howMany)

--Set values all different
for i = 1 to howMany  by 1 do
  seq1[i] = seq1[i] * i
end for

? bytes(howMany)          --IE, an integer uses  4 bytes
? bytes(1.1)              --IE, a  float   uses 16 bytes
? bytes(seq1)             --A seq uses 24 + 4 per integer + 16 per float
? seq1                    --Note, autoconversion to integer for term 10
? (bytes(seq1) - 24) / howMany  --IE, a numerical seq length is not predictable

--just a check
? integer(seq1[9])
? integer(seq1[10])

--Pointer arithmetic for a numeric sequence not a good idea.

--Arthur P. Adamson, The Engine Man, euclid at isoc.net