Here's a short program that does this with byte-at-a-time arithmetic. You can make it do word-at-a-time with a little playing, which should be faster. 
#!/usr/bin/perl -w

use strict;

use constant WORDBYTES => 1;
use constant WORDBITS => WORDBYTES*8;
use constant WORDNYBBLES => WORDBYTES*2;
use constant WORDMASK => (2**WORDBITS)-1;

sub left_shift_hex_string
{
  my($bits,$str,$add)=@_;
  my $val = hex(substr($str,0,WORDNYBBLES));
  my $carryout = $val >> (2**WORDBYTES-$bits);

  if (length($str) > WORDNYBBLES)
  {
    my($carryin,$res)=left_shift_hex_string($bits,substr($str,WORDNYBB
+LES),$add);
    return ($carryout,sprintf "%x%s", ($val<<$bits | $carryin) & WORDM
+ASK, $res);
  }
  else
  {
    warn "val=$val, bits=$bits, add=$add\n";
    return($carryout,sprintf "%x", ($val<<$bits|$add)&WORDMASK);
  }
}


my($co,$val)=left_shift_hex_string(1,"00ffffff",0);

print "val=$val\n";

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In reply to Re: Bit by a Hex String by sgifford
in thread Bit by a Hex String by abitkin

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