`set_upkara', `set_uptkara', `set_upfft'
----------------------------------------

set_upkara([THRESHOLD])
set_uptkara([THRESHOLD])
set_upfft([THRESHOLD])
     :: 1 $BJQ?tB?9`<0$N@Q1i;;$K$*$1$k(B N^2 , Karatsuba, FFT
     $B%"%k%4%j%:%`$N@ZBX$($NogCM(B

RETURN
     $B@_Dj$5$l$F$$$kCM(B

THRESHOLD
     $BHsIi@0?t(B

   * $B$$$:$l$b(B, $B0lJQ?tB?9`<0$N@Q$N7W;;$K$*$1$k(B,
     $B%"%k%4%j%:%`@ZBX$($NogCM$r(B $B@_Dj$9$k(B.

   * $B0lJQ?tB?9`<0$N@Q$O(B, $B<!?t(B N $B$,>.$5$$HO0O$G$ODL>o$N(B N^2
     $B%"%k%4%j%:%`(B, $BCfDxEY(B $B$N>l9g(B Karatsuba $B%"%k%4%j%:%`(B, $BBg$-$$>l9g$K$O(B
     FFT $B%"%k%4%j%:%`$G7W;;(B $B$5$l$k(B. $B$3$N@ZBX$($N<!?t$r@_Dj$9$k(B.

   * $B>\:Y$O(B, $B$=$l$>$l$N@Q4X?t$N9`$r;2>H$N$3$H(B.

$B;2>H(B
     *Note `kmul ksquare ktmul': kmul ksquare ktmul, *Note `umul
     umul_ff usquare usquare_ff utmul utmul_ff': umul umul_ff usquare
     usquare_ff utmul utmul_ff.

