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Unsigned Shift Right

Monkey Forums/Monkey Programming/Unsigned Shift Right

Samah(Posted 2012) [#1]
Can we please get an unsigned shift right operator? Something like "Shru". Also, fix the description of Shr on the wiki, because at the moment it defines Shr as "Bitwise shift left (signed)".


therevills(Posted 2012) [#2]
Do all targets support unsigned shifting?

BTW BlitzMax doesnt have it:
:Shl
Bitwise shift-left

:Shr
Bitwise shift-right

:Sar
Bitwise arithmetic shift-right



Samah(Posted 2012) [#3]
If the language doesn't natively support it, it's not hard to do it manually.


skid(Posted 2012) [#4]
In BlitzMax Shr is "unsigned" and Sar is "signed".


therevills(Posted 2012) [#5]
Ahh... looks like we have a small bug in MonkeyMax then :P

BlitzMax:
[bbcode]Local a:Int = -858993460 ' binary: 11001100110011001100110011001100
Local o1:Int = a Shl 6 ' left shift
Local o2:Int = a Shr 6 ' unsigned right shift
Local o3:Int = a Sar 6 ' signed right shift

Print ("a = "+a)
Print ("ol1 = "+o1)
Print ("ol2 = "+o2)
Print ("ol3 = "+o3)[/bbcode]

Outputs:
a   = -858993460
ol1 = 858993408
ol2 = 53687091
ol3 = -13421773


Monkey:
[monkeycode]Function Main()
Local a:Int = -858993460 ' binary: 11001100110011001100110011001100
Local o1:Int = a Shl 6 ' left shift
Local o2:Int = a Shr 6 ' signed right shift
'Local o3:Int = a Sar 6 ' signed right shift

Print ("a = "+a)
Print ("ol1 = "+o1)
Print ("ol2 = "+o2)
'Print ("ol3 = "+o3)
End[/monkeycode]

Outputs
a   = -858993460
ol1 = 858993408
ol2 = -13421773



I converted this Java example: http://www.herongyang.com/Java/Byte-Data-Type-Shift-Operations.html
/**
 * ShiftOperations.java
 * Copyright (c) 2006 by Dr. Herong Yang, http://www.herongyang.com/
 */
public class ShiftOperations {
   public static void main(String[] arg) {
      int a = -858993460; // binary: 11001100110011001100110011001100

      int o1 = a << 6;  // left shift
      int o2 = a >> 6;  // right shift
      int o3 = a >>> 6; // unsigned right shift

      System.out.println(" a: "+getBitString(a) +" = "+a);
      System.out.println("o1: "+getBitString(o1) +" = "+o1);
      System.out.println("o2: "+getBitString(o2) +" = "+o2);
      System.out.println("o3: "+getBitString(o3) +" = "+o3);
   }
   private static String getBitString(int x) {
      StringBuffer buf = new StringBuffer();
      for (int i=1; i<=32; i++) buf.append(x>>>(32-i) & 0x00000001);
      return buf.toString();
   }
}

The output of the test program matches my earlier examples: 

 a: 11001100110011001100110011001100 = -858993460
o1: 00110011001100110011001100000000 = 858993408
o2: 11111111001100110011001100110011 = -13421773
o3: 00000011001100110011001100110011 = 53687091



Goodlookinguy(Posted 2012) [#6]
I made logical shift functions a while ago here: http://monkeycoder.co.nz/Community/posts.php?topic=1707#28645 I even updated it with a MonkeyMax target last month.


GW_(Posted 2012) [#7]
Does this help? (vb)
http://pastebin.com/jRteLV58


therevills(Posted 2012) [#8]
I even updated it with a MonkeyMax target last month.

The fix to MonkeyMax actually needs to be done within the trans target code, because right now if you do a Shr in Monkey it will do a Shr in BlitzMax, whereas it really should convert Shr to Sar.