LN(natural log)

[anj]

I rewrote the "by calc" section from the following site
http://www.emesys.com/BS2math3.htm
into a subroutine and ended up with the following
Result is the log value multiplied by 1000
Accuracy should be good enough for what you are doing.
If you want to know HOW it works, you need to read the text, i just rewrote it and it worked so i was happy.

LogNo  VAR WORD     ' Number to get log of

k      VAR byte     'loop var
X      Var WORD     'temp for processing
X1     var word     'temp for squaring
LgX    var word     'lg ( base 2 ) of y the mantissa
cc     var byte     'characteristic of log

Lg     var word     'log base 2
Log    var word     'log base 10
Ln     var word     'log base e
'---------------------------------------------------
etc
etc
Logno = varX  'ie no to get result
gosub getlog
' now ref to Lg, Ln or Log as reqd

GetLog:
  cc = NCD LogNo - 1
  X = LogNo << ( 15 - cc )
  LgX = 0
  for k = 14 to 0 step -1
    X1 = X**X
    if X1.bit15 then
      lgx = lgx | ( dcd k )   'set the bit
      X = X1
    else
      X = ( X1 << 1 ) + 1    'shift er over
    endif  
  next k  
  lg  = cc*1000 + ( lgx**20000/10 )
  log = ( lg ** 19728 )
  ln  = ( lg ** 45426 )
return  
---------------------

Andrew