UCS-4 → UTF-1

 sub u4code2u1code ($) {
   my $U = shift;
   return ($U) if $U <= 0x9F;
   return (0xA0, $U) if $U <= 0xFF;
   return (0xA1 + ( $U - 0x100 ) / 0xBE,
           T(     ( $U - 0x100 ) % 0xBE)) if $U <= 0x4015;
   return (0xF6 + ( $U - 0x4016 ) / ( 0xBE**2 ),
           T(     ( $U - 0x4016 ) / 0xBE % 0xBE),
           T(     ( $U - 0x4016 ) % 0xBE      )) if $U <= 0x38E2D;
   return (0xFC + ( $U - 0x38E2E ) / ( 0xBE**4 ),
           T(     ( $U - 0x38E2E ) / ( 0xBE**3 ) % 0xBE),
           T(     ( $U - 0x38E2E ) / ( 0xBE**2 ) % 0xBE),
           T(     ( $U - 0x38E2E ) /   0xBE      % 0xBE),
           T(     ( $U - 0x38E2E ) %   0xBE      ));
 }

 sub utf1code2ucs4code (@) {
   my ($x, $y, $z, $v, $w) = @_;
   return $x if @_ == 1 && $x <= 0x9F;
   return $y if $x == 0xA0;
   return ($x - 0xA1) * 0xBE + U($y) + 0x100
     if 0xA1 <= $x && $x <= 0xF5;
   return ($x - 0xF6) * ( 0xBE**2 ) + U($y) * 0xBE + U($z) + 0x4016
     if 0xF6 <= $x && $x <= 0xFB;
   return ($x - 0xFC) * ( 0xBE**4 ) + U($y) * ( 0xBE**3 )
              + U($z) * ( 0xBE**2 ) + U($v) * 0xBE
              + U($w) + 0x38E2E;
 }

 sub T ($) {
   my $z = shift;
   return $z + 0x21 if $z <= 0x5D;
   return $z + 0x42 if $z <= 0xBD;
   return $z - 0xBE if $z <= 0xDE;
   return $z - 0x60;
 }

 ## T(z) の逆関数
 sub U ($) {
   my $z = shift;
   return $z + 0xBE if $z <= 0x20;
   return $z - 0x21 if $z <= 0x7E;
   return $z + 0x60 if $z <= 0x9F;
   return $z - 0x42;
 }

[15] perl 5.8 とかの、 Encode module が動く perl でないと駄目です。

[14] Encode::Unicode::UTF1 https://suika.suikawiki.org/gate/cvs/perl/lib/Encode/Unicode/UTF1.pm