Re: IEEE-754 encode/decode

[KHMan <keinhong@...>]

Clark Snowdall wrote:
> Hello all,
>
> I'm a newbie here so be gentle ...
>
> I need to convert back and forth between a string of bytes (4 bytes, 32-bits), and IEEE-754 floating point.  Basically I need to read a byte stream from a network socket and convert those bytes to a number.
>
> For example I need to convert:
> x = string.char(0x42, 0x96, 0x00, 0x00)
>
> to:
> y = 74.0
>
> And vice versa. I understand the IEEE-754 standard and if pressed could probably muddle through writing something from scratch.  But as with any programmer, if someone's already done it or if it's already in the language somewhere, it would just be easier than reinventing the wheel.
>
> Any ideas folks?

From ChunkSpy, has been casually tested with a few numbers...

function convert(x)
  local sign = 1
  local mantissa = string.byte(x, 3) % 128
  for i = 2, 1, -1 do mantissa = mantissa * 256 + string.byte(x, 
i) end
  if string.byte(x, 4) > 127 then sign = -1 end
  local exponent = (string.byte(x, 4) % 128) * 2 +
                   math.floor(string.byte(x, 3) / 128)
  if exponent == 0 then return 0 end
  mantissa = (math.ldexp(mantissa, -23) + 1) * sign
  return math.ldexp(mantissa, exponent - 127)
end

To avoid any copyright ambiguity, I declare the above to be in 
public domain.

--
Cheers,
Kein-Hong Man (esq.)
Kuala Lumpur, Malaysia