0 votes
by David N. Williams (120 points)

Thanks for adding F~ to VfxForthOsx64.  I'm running this:

 VFX Forth 64 for Mac OS X x64

 © MicroProcessor Engineering Ltd, 1998-2020 

 Version: 5.11 Beta 2 [build 0310]

 Build date: 27 September 2020

Is this the appropriate place for a bug report?

My tests reveal a bug in F~ when called as 0e F~, which turns out to be

due to a failure to take into account that FSIGN does not consume its

argument.  The F~ doc comment also has a typo in the f3 positive case,

is missing the case f3 = zero, and needs to replace abs[f3*abs[f1+f2]]

by abs[f3*[abs[f1]+abs[f2]]] in the f3 negative case.

The following fix in FPSSE64S.fth passes all of my fprox tests.

: f~            \ F: f1 f2 f3 -- ; -- flag

\ *G Approximation function. If f3 is positive, flag is true if abs[f1-f2]

\ ** less than f3. IF f3 is zero, flag is true if f1 and f2 encodings are

\ ** the same. If f3 is negative, flag is true if abs[f1-f2] less than

\ ** abs[f3*[abs[f1]+abs[f2]]].

  fdup f0> if                           \ if f3 > 0

    frot frot  f- fabs \ -- f3 |f1-f2|

    f>  exit                            \ -- t/f ; SFP007


  fdup f0= if \ if f3 = 0

\   fdrop  fdup fsign >r

\   fover fsign >r

    fdrop fsign >r

    fswap fsign >r

    f= r> r> xor 0= and  exit


  frot frot  fover fover \ -- f3 f1 f2 f1 f2

  f- fabs \ -- f3 f1 f2 |f1-f2|

  frot frot \ -- f3 |f1-f2| f1 f2

  fabs fswap fabs \ -- f3 |f1-f2| |f1| |f2|

  f+ frot fabs f* \ -- |f1-f2| |f3|*(|f1|+|f2|)

  f< \ -- t/f


1 Answer

0 votes
by Stephen Pelc (4.1k points)
Thanks for that. The new code will be available in Beta 3, due sometime this week providing that no supplier screws up our systems again.