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General => Technical support => Topic started by: Lorne Van Dusen on May 25, 2017, 06:07:57 PM

Title: reversing bits
Post by: Lorne Van Dusen on May 25, 2017, 06:07:57 PM

I did a search on the Internet for how to reverse bits and was surprised to find out how many times people have asked that question however most answers were for a C or C++
is there a simple way to reverse the bits in either a 8 bit or 16 bit value stored say in DM1 in TBASIC Fx series plc
example dm1 = 11100000 the result should be 00000111

Title: Re:reversing bits
Post by: support on May 26, 2017, 08:36:14 AM

Below is a 16 bit reverse bit example.

A = &HF5A0  ' put any value you want in A

B = 0

FOR I = 0 to 15
   IF TESTBIT(A, 15-I)
      SETBIT B, I
   ELSE
      CLRBIT B, I
   ENDIF
NEXT

' Result: B = &H05AF if A=&HF5A0

Title: Re:reversing bits
Post by: garysdickinson on May 26, 2017, 08:47:51 AM

You can eliminate the "else" clause in the "if" statement as all of the bits in B have been set to 0 outside the for loop:

B = 0

FOR I = 0 to 15
   IF TESTBIT(A, 15-I)
      SETBIT B, I
   ENDIF
NEXT


Gary D