Doing low-level unsigned arithmetic can be awkward in perl.

yupo

ok so i developed an overly debugged version of mix and the revised mix4 and ran it on the 32 bit box

# this is inside a 'use integer;' block 
sub mix4 ($$$) {
# per http://www.perlmonks.org/?node_id=1203705 this is a revised 32bi
+t under 'use integer'; 
    $_[A] -= $_[B]; $_[A] -= $_[C]; { no integer; $_[A] ^= ($_[C]>>13)
+; }
    $_[B] -= $_[C]; $_[B] -= $_[A]; { no integer; $_[B] ^= ($_[A]<< 8)
+; } 
    $_[C] -= $_[A]; $_[C] -= $_[B]; { no integer; $_[C] ^= ($_[B]>>13)
+; } 
    $_[A] -= $_[B]; $_[A] -= $_[C]; { no integer; $_[A] ^= ($_[C]>>12)
+; } 
    $_[B] -= $_[C]; $_[B] -= $_[A]; { no integer; $_[B] ^= ($_[A]<<16)
+; } 
    $_[C] -= $_[A]; $_[C] -= $_[B]; { no integer; $_[C] ^= ($_[B]>> 5)
+; } 
    $_[A] -= $_[B]; $_[A] -= $_[C]; { no integer; $_[A] ^= ($_[C]>> 3)
+; } 
    $_[B] -= $_[C]; $_[B] -= $_[A]; { no integer; $_[B] ^= ($_[A]<<10)
+; } 
    $_[C] -= $_[A]; $_[C] -= $_[B]; { no integer; $_[C] ^= ($_[B]>>15)
+; }
}
[download]

This is mix

# there is no 'use integer;' here; 
sub mix ($$$) {
    $_[A] -= $_[B]; $_[A] -= $_[C]; $_[A] ^= ($_[C]>>13);
    $_[B] -= $_[C]; $_[B] -= $_[A]; $_[B] ^= ($_[A]<< 8);
    $_[C] -= $_[A]; $_[C] -= $_[B]; $_[C] ^= ($_[B]>>13);
    $_[A] -= $_[B]; $_[A] -= $_[C]; $_[A] ^= ($_[C]>>12);
    $_[B] -= $_[C]; $_[B] -= $_[A]; $_[B] ^= ($_[A]<<16);
    $_[C] -= $_[A]; $_[C] -= $_[B]; $_[C] ^= ($_[B]>> 5);
    $_[A] -= $_[B]; $_[A] -= $_[C]; $_[A] ^= ($_[C]>> 3);
    $_[B] -= $_[C]; $_[B] -= $_[A]; $_[B] ^= ($_[A]<<10);
    $_[C] -= $_[A]; $_[C] -= $_[B]; $_[C] ^= ($_[B]>>15);
}
[download]

and the results are very interesting

during the first modification of C mix4exp shows (it is best to look at the following using download version without wrap)

     a1-x c>13  : A   :            59743          0000e95f
     b1-x a< 8  :  B  :                                    -      -162
+9499560          9edfcf58
     c1-a       :   C :                                    -          
+                          -           -59741          ffff16a3
SV = IV(0xc5f738) at 0xc5f73c
  REFCNT = 1
  FLAGS = (PADMY,IOK,pIOK)
  IV = -59741
     c1-b       :   C :                                    -          
+                          -       1629439819          611f474b
SV = IV(0xc5f738) at 0xc5f73c
  REFCNT = 1
  FLAGS = (PADMY,IOK,pIOK)
  IV = 1629439819
     c1-x b>13       : orig 1  :                                 01100
+001000111110100011101001011          611f474b
                     : orig 2  :                                 10011
+110110111111100111101011000          9edfcf58
                     : >>13    :                                 00000
+000000001001111011011111110          0004f6fe
                     : res     :                                 01100
+001000110111011000110110101          611bb1b5
     c1-x b>13  :   C :                                    -          
+                          -       1629204917          611bb1b5

while mixexp shows 


     a1-x c>13  : A   :            59743          0000e95f
     b1-x a< 8  :  B  :                                    -      -162
+9499560          9edfcf58
     c1-a       :   C :                                    -          
+                          -           -59741          ffff16a3
SV = IV(0xc5f418) at 0xc5f41c
  REFCNT = 1
  FLAGS = (PADMY,IOK,pIOK)
  IV = -59741
     c1-b       :   C :                                    -          
+                          -      -2147483648          80000000
SV = PVNV(0xc7355c) at 0xc5f41c
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  IV = -59741
  NV = -2665527477
  PV = 0
     c1-x b>13       : orig 1  :                                 10000
+000000000000000000000000000          80000000
                     : orig 2  :                                 10011
+110110111111100111101011000          9edfcf58
                     : >>13    :                                 00000
+000000001001111011011111110          0004f6fe
                     : res     :                                 10000
+000000001001111011011111110          8004f6fe
     c1-x b>13  :   C :                                    -          
+                          -      -2147158274          8004f6fe
[download]

The Dump calls are Dump($_[C]);

Notice that in mix4exp the Dump shows C stays IV, and shows the proper result of mod(32) arithmetic with A and B .

But notice how in mixexp the Dump shows that after -=A C has stayed IV, with the proper result, but that after -=B C overflowed the IV creating a NV and when it comes to the shift portion it is an overflow indicator (0x80000000) that gets shifted. Of course everything goes to L in a handbasket after that.

Doing low-level unsigned arithmetic can be awkward in perl.

yupo