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
then
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
then
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
;
