od: incorrect file offsets after first 16 bytes

* I observed the file offsets incorrectly jumped from 0 to 17, instead of 0 to 16
* When debugging this I discovered the formatting routines were modifying the value of $data by appending pad bytes
* Fix offsets issue by not modifying the value of $data
* Using global $len in the format routines is also not correct since the input loop was previously changed and $len will always be 1
* Remove global variable $upformat and provide the unpack format directly to unpack()
* Remove unsupported -a flag from the SYNOPSIS

bin/od

@@ -26,7 +26,7 @@ use vars qw/ $opt_A $opt_b $opt_c $opt_d $opt_f $opt_i $opt_j $opt_l $opt_N
 $opt_o $opt_v $opt_x /;
 
 my ($offset1, $radix, $data, @arr, $len, $fh, $lim);
-my ($lastline, $upformat, $pffmt, $strfmt, $ml);
+my ($lastline, $pffmt, $strfmt, $ml);
 
 my %charescs = (
     0  => ' \0',
@@ -168,19 +168,17 @@ close $fh;
 exit EX_SUCCESS;
 
 sub octal1 {
-    $upformat = 'C*'; # for -b
     $pffmt = '%.3o ';
-    @arr = unpack($upformat,$data);
+    @arr = unpack 'C*', $data;
     $strfmt = $pffmt x (scalar @arr);
 }
 
 sub char1 {
-    $upformat = 'C*'; # for -c
     $pffmt = '%s';
     $strfmt = $pffmt;
 
     @arr = ();
-    my @arr1 = unpack($upformat,$data);
+    my @arr1 = unpack 'C*', $data;
     for my $val (@arr1) {
         if (exists $charescs{$val}) {
 	    $arr[0] .= $charescs{$val} . " ";
@@ -195,52 +193,72 @@ sub char1 {
 }
 
 sub udecimal {
-    $upformat = 'S*'; # for -d
-    $data .= "\0" if ($len & 1); # zero-fill 16 bit input
+    if (length($data) & 1) { # pad to 16 bit
+        @arr = unpack 'S*', $data . "\0";
+    }
+    else {
+        @arr = unpack 'S*', $data;
+    }
     $pffmt = '%5u ';
-    @arr = unpack($upformat,$data);
     $strfmt = $pffmt x (scalar @arr);
 }
 
 sub float {
-    $upformat = 'f*'; # for -f
-    my $remain = $len % 4;
-    $data .= "\0" x $remain if ($remain); # zero-fill 32 bit input
+    my $remain = length($data) % 4;
+    if ($remain) { # pad to 32 bit
+        my $pad = "\0" x $remain;
+        @arr = unpack 'f*', $data . $pad;
+    }
+    else {
+	@arr = unpack 'f*', $data;
+    }
     $pffmt = '%6.6e ';
-    @arr = unpack($upformat,$data);
     $strfmt = $pffmt x (scalar @arr);
 }
 
 sub decimal {
-    $upformat = 's*'; # for -i
-    $data .= "\0" if ($len & 1); # zero-fill 16 bit input
+    if (length($data) & 1) { # pad to 16 bit
+        @arr = unpack 's*', $data . "\0";
+    }
+    else {
+        @arr = unpack 's*', $data;
+    }
     $pffmt = '%5d ';
-    @arr = unpack($upformat,$data);
     $strfmt = $pffmt x (scalar @arr);
 }
 
 sub long {
-    $upformat = 'L*'; # for -l
-    my $remain = $len % 4;
-    $data .= "\0" x $remain if ($remain); # zero-fill 32 bit input
+    my $remain = length($data) % 4;
+    if ($remain) { # pad to 32 bit
+        my $pad = "\0" x $remain;
+        @arr = unpack 'L*', $data . $pad;
+    }
+    else {
+	@arr = unpack 'L*', $data;
+    }
     $pffmt = '%10ld ';
-    @arr = unpack($upformat,$data);
     $strfmt = $pffmt x (scalar @arr);
 }
 
 sub octal2 {
-    $upformat = 'S*'; # for -o
-    $data .= "\0" if ($len & 1); # zero-fill 16 bit input
+    if (length($data) & 1) { # pad to 16 bit
+        @arr = unpack 'S*', $data . "\0";
+    }
+    else {
+        @arr = unpack 'S*', $data;
+    }
     $pffmt = '%.6o ';
-    @arr = unpack($upformat,$data);
     $strfmt = $pffmt x (scalar @arr);
 }
 
 sub hex {
-    $upformat = 'S*'; # for -x
-    $data .= "\0" if ($len & 1); # zero-fill 16 bit input
+    if (length($data) & 1) { # pad to 16 bit
+        @arr = unpack 'S*', $data . "\0";
+    }
+    else {
+        @arr = unpack 'S*', $data;
+    }
     $pffmt = '%.4x ';
-    @arr = unpack($upformat,$data);
     $strfmt = $pffmt x (scalar @arr);
 }
 
@@ -261,7 +279,7 @@ od - dump files in octal and other formats
 
 =head1 SYNOPSIS
 
-B<od> [ I<-abcdfiloxv> ] [I<-j skip_n_bytes>] [I<-N read_n_bytes>] [ I<-A radix> ]  F<filename>
+B<od> [ I<-bcdfiloxv> ] [I<-j skip_n_bytes>] [I<-N read_n_bytes>] [ I<-A radix> ]  F<filename>
 
 =head1 DESCRIPTION