14, 11

14
    x11
   _____
     14
    14
  ______
    154

-7, 20

-7
    x20
   _____
     00
    14
   _____
   -140

($x,$y)=<>=~/[-d]+/g;printf"%7s
",$_ for$x,x.$y,"-"x7,(map{abs($x*$_).$"x$i++}reverse$y=~/d/g),"-"x7,$x*$y

sub P{sprintf"%*d",@_}
($x,$y)=<>=~/[^,]+/g;$,=$/;
print P(7,$x),"  x".P(4,$y),"-"x7,(map{P 7-$i++,abs$_*$x}reverse$y=~/d/g),
"-"x7,P 7,$x*$y

a_~g~b_ :=
With[{e = IntegerDigits@b}, Column[Flatten@{a, UnderBar["x " <> IntegerString[b]],
Table[Row @@ {PadRight[{a Reverse[e][[i]]}, i, " "]}, {i, Length@e}], OverBar[a b]},
Alignment -> Right]]

g[845, 921]

a,b=input();r,s=str(a),str(b);h=len(r+s)*'-';print'n'.join(["%9sn%9sn%9s"%(r,'x'+s,h)]+["%%%ii"%(9-i)%(int(d)%10*a)for i,d in enumerate(s[::-1])]+["%9sn%9i"%(h,a*b)])

1234
    x5678
 --------
     9872
    8638
   7404
  6170
 --------
  7006652

a,b=input();h=6*'-';print'n'.join(["%6inx%5in%s"%(a,b,h)]+["%%%ii"%(6-i)%(int(d)%10*a)for i,d in enumerate(str(b)[::-1])]+["%sn%6i"%(h,a*b)])

999
x  999
------
  8991
 8991
8991
------
998001

($x,$y)=<>=~/[-d]+/g;map{$z=~s/z/ z/g;$z=(abs$x*$_)."z$z"}split//,abs$y;map{printf"%6s
",$_}$x,"x$y",$b="-"x6,(split/z/,$z),$b,$x*$y

>echo "-123, 456" | perl mult.pl
   -123
   x456
-------
    738
   615
  492
-------
 -56088