[metapost] a "randomseed" workaround

[Larry Siebenmann]

Hello all,

Since,  in many mp implementations, the automatic
"uniformdeviate" and "normaldeviate" seeding mechanism of
mp is not sufficiently responsive to the passage of time,
I offer the following simple workaround -- that usefully
softens Taco's verdict (Mon, 28 Feb 2005):

 > Setting seeds is system-dependant (because all portable
 > solutions depend on the current time)

     It took me quite a while to locate the conversion
from string to numeric by "scantokens" (see below).
Nothing about it in mp documentation; its not a syntax one
easily infers from other languages.  It would be helpful
to add to mp documentation a fairly complete table of
primitives that are common to mf and mp.

     I've updated "ProfileBezier.mp" at

     http://topo.math.u-psud.fr/~lcs/mp/ProfileBezier/

since it benefits noticeably.

     It took me quite a while to locate the conversion
from string to numeric by "scantokens" (see below).
Nothing about it in mp documentation; its not a syntax one
easily infers from other languages.  It would be helpful
to add to mp documentation a fairly complete table of
primitives that are common to mf and mp.  Seems only 
the differences are systematically listed.

Cheers

Laurent S.


%%% Patch for a mp file that uses
%%% uniformdeviate or normaldeviate
%%% and can be expected to run more often than
%%% "randomseed" is updated.
%%% Belongs in header.
string str;
numeric seed_adjuvant;
%
str:=readfrom "SeedBank";
%show str;
if str = EOF: 
  write "1" to "SeedBank";
  write EOF to "SeedBank";
  seed_adjuvant:=0
else:
  seed_adjuvant:= scantokens(str);
  seed_adjuvant:= (seed_adjuvant+1) mod 3600;
  write (decimal seed_adjuvant) to "SeedBank";
  write EOF to "SeedBank";
fi;
%
randomseed:= day + (time + seed_adjuvant)*epsilon;
%
%% Default for metafont is (in effect) 
%% randomseed:= day + time*epsilon
%%% End of patch.