#! perl -slw
use strict;
use Digest::MD5 qw[ md5 ];

sub crc64 {
    my $data = shift;
    my $crc = "";
    my $len = length( $$data );
    my $pos = 0;
    while ( $pos < $len ) {
        $crc = $crc ^ substr( $$data, $pos, 8 );
        $pos += 8;
    }
    return ( $crc );
}

our $C //= 16;

my $text = join '', map chr( rand 256 ), 1 .. 16;
my $md5text = md5( $text );
my $crctext = crc64( \$text );
my $copy = $text;

my $md5changes = 0;
my $crcchanges = 0;
for my $bit ( 0 .. 16*8 -1 ) {
    vec( $copy, $bit, 1 ) ^= 1; ## toggle this bit

    my $md5copy = md5( $copy );
    my $md5changed = unpack '%32B*', $md5text ^ $md5copy;
    $md5changes += $md5changed;

    my $crccopy = crc64( \$copy );
    my $crcchanged = unpack '%32B*', $crctext ^ $crccopy;
    $crcchanges += $crcchanged;

    print "Toggling bit:$bit produced MD5[$md5changed] CRC[$crcchanged] changes";

    vec( $copy, $bit, 1 ) ^= 1; ## toggle it back
}

printf "Average MD5[changes: %.3f bits] CRC[changes: %.3f bits] per input bit changed\n",
    $md5changes / ( 16*8 ), $crcchanges / ( 16*8 );

__END__
C:\test>t-md5rand -C=4
Toggling bit:0 produced MD5[68] CRC[1] changes
Toggling bit:1 produced MD5[52] CRC[1] changes
Toggling bit:2 produced MD5[66] CRC[1] changes
Toggling bit:3 produced MD5[75] CRC[1] changes
Toggling bit:4 produced MD5[64] CRC[1] changes
Toggling bit:5 produced MD5[61] CRC[1] changes
Toggling bit:6 produced MD5[65] CRC[1] changes
Toggling bit:7 produced MD5[64] CRC[1] changes
Toggling bit:8 produced MD5[54] CRC[1] changes
Toggling bit:9 produced MD5[58] CRC[1] changes
Toggling bit:10 produced MD5[66] CRC[1] changes
Toggling bit:11 produced MD5[74] CRC[1] changes
Toggling bit:12 produced MD5[67] CRC[1] changes
Toggling bit:13 produced MD5[76] CRC[1] changes
Toggling bit:14 produced MD5[66] CRC[1] changes
Toggling bit:15 produced MD5[57] CRC[1] changes
Toggling bit:16 produced MD5[73] CRC[1] changes
Toggling bit:17 produced MD5[56] CRC[1] changes
Toggling bit:18 produced MD5[71] CRC[1] changes
Toggling bit:19 produced MD5[61] CRC[1] changes
Toggling bit:20 produced MD5[63] CRC[1] changes
Toggling bit:21 produced MD5[64] CRC[1] changes
Toggling bit:22 produced MD5[66] CRC[1] changes
Toggling bit:23 produced MD5[60] CRC[1] changes
Toggling bit:24 produced MD5[53] CRC[1] changes
Toggling bit:25 produced MD5[64] CRC[1] changes
Toggling bit:26 produced MD5[72] CRC[1] changes
Toggling bit:27 produced MD5[72] CRC[1] changes
Toggling bit:28 produced MD5[65] CRC[1] changes
Toggling bit:29 produced MD5[68] CRC[1] changes
Toggling bit:30 produced MD5[48] CRC[1] changes
Toggling bit:31 produced MD5[61] CRC[1] changes
Toggling bit:32 produced MD5[65] CRC[1] changes
Toggling bit:33 produced MD5[57] CRC[1] changes
Toggling bit:34 produced MD5[60] CRC[1] changes
Toggling bit:35 produced MD5[65] CRC[1] changes
Toggling bit:36 produced MD5[64] CRC[1] changes
Toggling bit:37 produced MD5[58] CRC[1] changes
Toggling bit:38 produced MD5[69] CRC[1] changes
Toggling bit:39 produced MD5[64] CRC[1] changes
Toggling bit:40 produced MD5[62] CRC[1] changes
Toggling bit:41 produced MD5[64] CRC[1] changes
Toggling bit:42 produced MD5[71] CRC[1] changes
Toggling bit:43 produced MD5[61] CRC[1] changes
Toggling bit:44 produced MD5[64] CRC[1] changes
Toggling bit:45 produced MD5[61] CRC[1] changes
Toggling bit:46 produced MD5[71] CRC[1] changes
Toggling bit:47 produced MD5[73] CRC[1] changes
Toggling bit:48 produced MD5[65] CRC[1] changes
Toggling bit:49 produced MD5[56] CRC[1] changes
Toggling bit:50 produced MD5[58] CRC[1] changes
Toggling bit:51 produced MD5[61] CRC[1] changes
Toggling bit:52 produced MD5[66] CRC[1] changes
Toggling bit:53 produced MD5[60] CRC[1] changes
Toggling bit:54 produced MD5[66] CRC[1] changes
Toggling bit:55 produced MD5[63] CRC[1] changes
Toggling bit:56 produced MD5[64] CRC[1] changes
Toggling bit:57 produced MD5[63] CRC[1] changes
Toggling bit:58 produced MD5[57] CRC[1] changes
Toggling bit:59 produced MD5[66] CRC[1] changes
Toggling bit:60 produced MD5[66] CRC[1] changes
Toggling bit:61 produced MD5[59] CRC[1] changes
Toggling bit:62 produced MD5[63] CRC[1] changes
Toggling bit:63 produced MD5[72] CRC[1] changes
Toggling bit:64 produced MD5[59] CRC[1] changes
Toggling bit:65 produced MD5[64] CRC[1] changes
Toggling bit:66 produced MD5[65] CRC[1] changes
Toggling bit:67 produced MD5[64] CRC[1] changes
Toggling bit:68 produced MD5[68] CRC[1] changes
Toggling bit:69 produced MD5[68] CRC[1] changes
Toggling bit:70 produced MD5[67] CRC[1] changes
Toggling bit:71 produced MD5[61] CRC[1] changes
Toggling bit:72 produced MD5[64] CRC[1] changes
Toggling bit:73 produced MD5[69] CRC[1] changes
Toggling bit:74 produced MD5[73] CRC[1] changes
Toggling bit:75 produced MD5[68] CRC[1] changes
Toggling bit:76 produced MD5[57] CRC[1] changes
Toggling bit:77 produced MD5[53] CRC[1] changes
Toggling bit:78 produced MD5[59] CRC[1] changes
Toggling bit:79 produced MD5[63] CRC[1] changes
Toggling bit:80 produced MD5[74] CRC[1] changes
Toggling bit:81 produced MD5[65] CRC[1] changes
Toggling bit:82 produced MD5[73] CRC[1] changes
Toggling bit:83 produced MD5[66] CRC[1] changes
Toggling bit:84 produced MD5[62] CRC[1] changes
Toggling bit:85 produced MD5[53] CRC[1] changes
Toggling bit:86 produced MD5[55] CRC[1] changes
Toggling bit:87 produced MD5[60] CRC[1] changes
Toggling bit:88 produced MD5[61] CRC[1] changes
Toggling bit:89 produced MD5[68] CRC[1] changes
Toggling bit:90 produced MD5[69] CRC[1] changes
Toggling bit:91 produced MD5[64] CRC[1] changes
Toggling bit:92 produced MD5[66] CRC[1] changes
Toggling bit:93 produced MD5[65] CRC[1] changes
Toggling bit:94 produced MD5[66] CRC[1] changes
Toggling bit:95 produced MD5[64] CRC[1] changes
Toggling bit:96 produced MD5[50] CRC[1] changes
Toggling bit:97 produced MD5[68] CRC[1] changes
Toggling bit:98 produced MD5[59] CRC[1] changes
Toggling bit:99 produced MD5[60] CRC[1] changes
Toggling bit:100 produced MD5[65] CRC[1] changes
Toggling bit:101 produced MD5[64] CRC[1] changes
Toggling bit:102 produced MD5[48] CRC[1] changes
Toggling bit:103 produced MD5[62] CRC[1] changes
Toggling bit:104 produced MD5[66] CRC[1] changes
Toggling bit:105 produced MD5[61] CRC[1] changes
Toggling bit:106 produced MD5[63] CRC[1] changes
Toggling bit:107 produced MD5[68] CRC[1] changes
Toggling bit:108 produced MD5[70] CRC[1] changes
Toggling bit:109 produced MD5[62] CRC[1] changes
Toggling bit:110 produced MD5[57] CRC[1] changes
Toggling bit:111 produced MD5[60] CRC[1] changes
Toggling bit:112 produced MD5[68] CRC[1] changes
Toggling bit:113 produced MD5[68] CRC[1] changes
Toggling bit:114 produced MD5[49] CRC[1] changes
Toggling bit:115 produced MD5[64] CRC[1] changes
Toggling bit:116 produced MD5[55] CRC[1] changes
Toggling bit:117 produced MD5[57] CRC[1] changes
Toggling bit:118 produced MD5[57] CRC[1] changes
Toggling bit:119 produced MD5[71] CRC[1] changes
Toggling bit:120 produced MD5[70] CRC[1] changes
Toggling bit:121 produced MD5[62] CRC[1] changes
Toggling bit:122 produced MD5[70] CRC[1] changes
Toggling bit:123 produced MD5[67] CRC[1] changes
Toggling bit:124 produced MD5[52] CRC[1] changes
Toggling bit:125 produced MD5[70] CRC[1] changes
Toggling bit:126 produced MD5[73] CRC[1] changes
Toggling bit:127 produced MD5[59] CRC[1] changes
Average MD5[changes: 63.531 bits] CRC[changes: 1.000 bits] per input bit changed