The optomiser eliminates any differences. Yours (c_luhn3 below) can be slightly faster one run and slightly slower on the next; but the difference is less that 0.5% either way:
#! perl -slw
use strict;
use Inline C => Config => BUILD_NOISY => 1;
use Inline C => <<'END_C', NAME => '_luhn', CLEAN_AFTER_BUILD =>0;
int c_luhn( char *s ) {
int i, total = 0;
for( i=0; i < 15; ++i ) {
int d = s[ i ] - '0';
if( !( i & 1 ) ) {
d *= 2;
if( d > 9 ) d -= 9;
}
total += d;
}
total *= 9;
return total % 10;
}
int l[] = { 0, 2, 4, 6, 8, 1, 3, 5, 7, 9 };
int c_luhn2( char *s ) {
int total = 0;
total += l[ s[ 0] - '0' ];
total += s[ 1] - '0';
total += l[ s[ 2] - '0' ];
total += s[ 3] - '0';
total += l[ s[ 4] - '0' ];
total += s[ 5] - '0';
total += l[ s[ 6] - '0' ];
total += s[ 7] - '0';
total += l[ s[ 8] - '0' ];
total += s[ 9] - '0';
total += l[ s[10] - '0' ];
total += s[11] - '0';
total += l[ s[12] - '0' ];
total += s[13] - '0';
total += l[ s[14] - '0' ];
total *= 9;
return total % 10;
}
int ll[] = {
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 2, 4, 6, 8, 1, 3, 5, 7, 9 };
int
c_luhn3( char *s ) {
return ((
ll[ (int)s[ 0] ]
+ s[ 1]
+ ll[ (int)s[ 2] ]
+ s[ 3]
+ ll[ (int)s[ 4] ]
+ s[ 5]
+ ll[ (int)s[ 6] ]
+ s[ 7]
+ ll[ (int)s[ 8] ]
+ s[ 9]
+ ll[ (int)s[10] ]
+ s[11]
+ ll[ (int)s[12] ]
+ s[13]
+ ll[ (int)s[14] ] - 7 * '0' ) * 9) % 10;
}
END_C
use Time::HiRes qw[ time ];
my @samples = qw[
4011350000000008
4011350000000016
4011350000000024
4011350000000032
4011350000000040
4011350000000057
4011350000000065
4011350000000073
4011350000000081
4011350000000099
];
sub luhn {
use integer;
my $s = $_[ 0 ];
my $total = 0;
for my $i ( 0 .. 14 ) {
my $d = substr( $s, $i, 1 );
unless( $i & 1 ) {
$d *= 2;
$d -= 9 if $d > 9;
}
$total += $d;
}
$total *= 9;
return chop $total;
}
for ( @samples ) {
print "$_: ", luhn( substr $_, 0, 15 );
}
my $start = time;
#for ( 401135000000000..401135000999999 ) {
# my $chk = luhn( $_ );
#}
#printf "Took %.9f seconds.\n", time() - $start;
#for ( @samples ) {
# print "$_: ", c_luhn( $_ );
#}
$start = time;
for ( 401135000000000..401135000999999 ) {
my $chk = c_luhn( $_ );
}
printf "Took %.9f seconds.\n", time() - $start;
for ( @samples ) {
print "$_: ", c_luhn2( $_ );
}
$start = time;
for ( 401135000000000..401135000999999 ) {
my $chk = c_luhn2( $_ );
}
printf "Took %.9f seconds.\n", time() - $start;
for ( @samples ) {
print "$_: ", c_luhn3( $_ );
}
$start = time;
for ( 401135000000000..401135000999999 ) {
my $chk = c_luhn3( $_ );
}
printf "Took %.9f seconds.\n", time() - $start;
C:\test>luhn
4011350000000008: 8
4011350000000016: 6
4011350000000024: 4
4011350000000032: 2
4011350000000040: 0
4011350000000057: 7
4011350000000065: 5
4011350000000073: 3
4011350000000081: 1
4011350000000099: 9
Took 0.751899958 seconds.
4011350000000008: 8
4011350000000016: 6
4011350000000024: 4
4011350000000032: 2
4011350000000040: 0
4011350000000057: 7
4011350000000065: 5
4011350000000073: 3
4011350000000081: 1
4011350000000099: 9
Took 0.695394039 seconds.
4011350000000008: 8
4011350000000016: 6
4011350000000024: 4
4011350000000032: 2
4011350000000040: 0
4011350000000057: 7
4011350000000065: 5
4011350000000073: 3
4011350000000081: 1
4011350000000099: 9
Took 0.693738222 seconds.
C:\test>luhn
4011350000000008: 8
4011350000000016: 6
4011350000000024: 4
4011350000000032: 2
4011350000000040: 0
4011350000000057: 7
4011350000000065: 5
4011350000000073: 3
4011350000000081: 1
4011350000000099: 9
Took 0.751657963 seconds.
4011350000000008: 8
4011350000000016: 6
4011350000000024: 4
4011350000000032: 2
4011350000000040: 0
4011350000000057: 7
4011350000000065: 5
4011350000000073: 3
4011350000000081: 1
4011350000000099: 9
Took 0.694734097 seconds.
4011350000000008: 8
4011350000000016: 6
4011350000000024: 4
4011350000000032: 2
4011350000000040: 0
4011350000000057: 7
4011350000000065: 5
4011350000000073: 3
4011350000000081: 1
4011350000000099: 9
Took 0.697062969 seconds.
With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
In the absence of evidence, opinion is indistinguishable from prejudice.
Suck that fhit
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