#! perl -slw
use strict;
use Benchmark qw[cmpthese];

our $n = "\xf0\x0f";

print unpack 'hhhh', $n;                            #! Gives >> 0 f
print unpack 'h h h h', $n;                         #! Gives >> 0 f
print unpack 'h2 h2', $n;                           #! Gives >> 0f f0 
+# two 2-byte strings
print unpack 'h4', $n;                              #! Gives >> 0ff0 #
+ a single 4 char string

print map{hex} (split'', unpack 'h4', $n)[2,3,0,1];                 #!
+ Gives >> 15 0 0 15
print map{ ( ord($_) & 0xf0 ) >> 4, ord($_) & 0x0f } split//, $n;   #!
+ Gives >> 15 0 0 15
print map{ vec $n, $_, 4 } 0 .. 3;                                  #!
+ Gives >> 0 15 15 0
print +(map{ vec $n, $_, 4 } 0 .. 3)[2,3,0,1];                      #!
+ Gives >> 15 0 0 15
print map{ ( unpack( 'n' , $n ) >> ( 4 * $_ ) ) & 0xf } 0 .. 3;     #!
+ Gives >> 15 0 0 15
$n = unpack 'n', $n; print map{ ($n >>( 4 * $_ )) & 0xf } 0 .. 3;   #!
+ Gives >> 15 0 0 15

our @nybbles = ();
cmpthese( -1, {
    #! 1 map, 4 hexes (Just my luck!), a split, an unpack, a list and 
+a slice.
    map_hex_split_unpack
    => q[ @nybbles = map{hex} (split'', unpack 'h4', $n)[2,3,0,1]; ],

    #! 1 map, 2 ords, 2 ands, shift right 4, 1 split and a partridge i
+n a pair tree!
    map_ord_and_shift_split
    => q[ @nybbles = map{ ( ord($_) & 0xf0 ) >> 4, ord($_) & 0x0f } sp
+lit//, $n; ],

    #! 1 map, 4 vecs, two lists, one splice. Phew!
    map_vec_lists_splice
    => q[ @nybbles = map{ ( unpack( 'n' , $n ) >> ( 4 * $_ ) ) & 0xf }
+ 0 .. 3; ],

    #! 1map, 4 X ( unpack, shift, mult, & ), a list
    #! and enough brackets to keep a LISP afficianardo happy for days.
    map_unpack_shift_mult_and_list
    => q[ @nybbles = map{ ( unpack( 'n' , $n ) >> ( 4 * $_ ) ) & 0xf }
+ 0 .. 3; ],

    #! Factor out the unpack. Slightly better.
    unpack_map_shift_and_list
    => q[ $n = unpack 'n', $n; @nybbles = map{ ( $n >> ( 4 * $_ ) ) & 
+0xf } 0 .. 3; ],
});

__DATA__
C:\test>test

map_hex_split_unpack:            1 wallclock secs  @ 10317.66/s (n=107
+51)
map_ord_and_shift_split:         1 wallclock secs  @  7324.69/s (n= 76
+25)
map_unpack_shift_mult_and_list:  2 wallclock secs  @ 12869.53/s (n=146
+97)
map_vec_lists_splice:            1 wallclock secs  @ 12954.41/s (n=133
+56)
unpack_map_shift_and_list:       1 wallclock secs  @ 15328.34/s (n=153
+59)

                                  Rate  MOASP   MHSU MUSMUL   MVLS    
+UMSL
map_ord_and_shift_split         7325/s    --    -29%  -43%    -43%    
+-52%
map_hex_split_unpack           10318/s    41%    --   -20%     20%    
+-33%
map_unpack_shift_mult_and_list 12870/s    76%    25%   --      -1%    
+-16%
map_vec_lists_splice           12954/s    77%    26%    1%     --     
+-15%
unpack_map_shift_and_list      15328/s   109%    49%   19%     18%    
+ --

C:\test>
[download]