Fast method for Reverse Sign Extend?

T Chap

I want to send out a signed long as a signed word, but don't see an operator that is the reverse of the signed extend from 15 to 31. I was wondering if there was a fast method in SPIN as single operator to move bit 31 to 15. Does anyone have a trick for a the fastest method in SPIN to move bit 31? All I can think of is:

If SignedLongVariable < 0
   WordVariable :=   %1000_0000_0000_0000  |=   SignedLongVariable   ' value does not exceed +/- 2000

' compute checksum
ser.tx(PacketHeader)
ser.tx(PacketLength)
ser.tx(Opcode)
ser.tx(WordVariable)
ser.tx(WordVariable>>8)
ser.tx(checksum)

Or

   WordVariable :=   SignedLongVariable +   SignedLongVariable  >> 16 

Phil Pilgrim (PhiPi)

Just use the lower 16 bits of the long. As long as there's no overflow, the result will be correct.

-Phil