> -----Original Message-----
> From: IBM Mainframe Assembler List
> [mailto:[email protected]] On Behalf Of Bill Fairchild
> Sent: Monday, August 23, 2010 1:04 PM
> To: [email protected]
> Subject: Re: Efficient Memory List
>
> Your random input entry is a 32-bit number. Two to the 32nd
> power is 4GB. Let the 32-bit number represent the number of
> a bit in a contiguous string of bits that is 4 billion bits
> long. The number of bytes to contain this array is 537 MB,
> which can easily be acquired above the bar or in a data
> space. Find the byte address and bit offset within that byte
> that corresponds to the 32-bit input number. Test the bit.
> If off, you have a new entry, so turn the bit on and process
> the new entry. If on, you have a duplicate entry, so ignore
> the entry.
>
> Bill Fairchild
> Rocket Software
Assuming truly random distribution of possible keys, couldn't this solution
possibly cause a fair amount of paging overhead? I really don't know. Was the
solution left off as an exercise for the reader? <grin> I'd use something like:
SR 15,15
L 14,VALUE
SRDL 14,3 OFFSET TO BYTE CONTAINING BIT TO TEST
SRL 15,29 BIT NUMBER TO TEST
L 1,TABLE_ADDRESS
LLC 2,BIT(15) SET BIT TO TEST INTO R2
LR 3,2 AND I NEED IT LATER, TOO
LLC 0,0(15,1) GET BYTE CONTAINING BIT TO TEST
NR 2,0 TEST BIT
JNZ ALREADY_SET
OR 3,0 SET BIT
STC 3,0(15,1) UPDATE THE BYTE
...
BIT DC AL1(128,64,32,16,8,4,2,1)
The code above is not thread safe (reentrant). I used LLC instead of IC because
LLC sets the other bits of the register to zero. This is needed for the NR and
saves an SR instruction to clear reg 0 that an IC would need.
--
John McKown
Systems Engineer IV
IT
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