HLASM - BCT = Branch on CounT

The opcode of the BCT instruction is X'46'.

Usage

The BCT instruction is intended for use at the end of a loop. That is, before starting the loop the number of iterations over the loop is set up in the count register. At the end of each pass over the loop the count is decremented and the loop is repeated until the count drops to zero.

  1. Decrement a counter to loop a specified number of times.

Arguments

  1. Register holding the current count.
  2. Destination address (index, base, displacement) where loop is to be resumed if count is not yet zero.

Function

  1. The processor decrements the register, which holds a count.
  2. Normally, the processor branches to the destination address, but if the count has just dropped to zero, then it continues with the next instruction.
  3. The condition code does not change.

Special Cases

  1. None.

Related Instructions

  1. BCTR loops to an address that is contained in a register.
  2. BCTGR uses a 64-bit counter and loops to an address that is contained in a register.
  3. BCTG uses a 64-bit counter.

Hardware

  1. All hardware supports the BCT instruction.

Remarks

  1. The PSW's Amode setting determines how many bits are used for the destination address.

Examples

         YREGS                          * Define register names
         ...
SETUP    LA    R2,12                    * Repeat 12 times
LOOP     EQU   *                        * Start of loop
         ...                            * Content of the loop goes here
         BCT   R2,LOOP                  * Repeat until count drops to 0
         ...

To the Opcodes Overview.
To the English Homepage for Hlasm.com.
To the General Homepage for Bixoft and Hlasm.com.

This site is a member of WebRing.
You are invited to browse the list of mainframe-loving sites. 		Running Tyrannosaurus Rex Dinos are not dead. They are alive and well and living in data centers all around you. They speak in tongues and work strange magics with computers. Beware the dino! And just in case you're waiting for the final demise of these dino's: remember that dinos ruled the world for 155-million years!
Dinos and other anachronisms
[ Join Now | Ring Hub | Random | << Prev | Next >> ]
 

Below you find the logo of our sponsor and logos of the web-standards that this page adheres to.

Text and sample code by Abe F. Kornelis and Lin Lyons.
© Copyright B.V. Bixoft, 2004-2006. All rights reserved.
Bixoft ® is a trademark of B.V. Bixoft
e-mail Bixoft.