Examples of moving data into and out of a data space

When using data spaces, you sometimes have large amounts of data to transfer between the address space and the data space. This information contains examples of two subroutines, both named COPYDATA, that show you how to use the Move (MVC) and Move Long (MVCL) instructions to move a variable number of bytes into and out of a data space. (You can also use the examples to help you move data within an address space.) The two examples perform exactly the same function; both are included here to show you the relative coding effort required to use each instruction.

The use of registers for the two examples is as follows: 
 Input:  AR/GR 2    Target area location
         AR/GR 3    Source area location
         GR 4       Signed 32-bit length of area
                    (Note: A negative length is treated as zero.)
         GR 14      Return address
 Output: AR/GR 2-14 Restored
         GR 15      Return code of zero

The routines can be called in either primary or AR mode; however, during the time they manipulate data in a data space, they must be in AR mode. The source and target locations are assumed to be the same length (that is, the target location is not filled with a padding character).

Example 1: Using the MVC Instruction: The first COPYDATA example uses the MVC instruction to move the specified data in groups of 256 bytes: 
COPYDATA DS    0D
         BAKR  14,0                  SAVE CALLER'S STATUS
         LAE   12,0(0,0)             BASE REG AR
         BALR  12,0                  BASE REG GR
         USING *,12                  ADDRESSABILITY
  .
         LTR   4,4                   IS LENGTH NEGATIVE OR ZERO?
         BNP   COPYDONE              YES, RETURN TO CALLER
  .
         S     4,=F'256'             SUBTRACT 256 FROM LENGTH
         BNP   COPYLAST              IF LENGTH NOW NEGATIVE OR ZERO
*                                    THEN GO COPY LAST PART
  .
COPYLOOP DS    0H
         MVC   0(256,2),0(3)         COPY 256 BYTES
         LA    2,256(,2)             ADD 256 TO TARGET ADDRESS
         LA    3,256(,3)             ADD 256 TO SOURCE ADDRESS
         S     4,=F'256'             SUBTRACT 256 FROM LENGTH
         BP    COPYLOOP              IF LENGTH STILL GREATER THAN
*                                    ZERO, THEN LOOP BACK
COPYLAST DS    0H
         LA    4,255(,4)             ADD 255 TO LENGTH
         EX    4,COPYINST            EXECUTE A MVC TO COPY THE
*                                    LAST PART OF THE DATA
         B     COPYDONE              BRANCH TO EXIT CODE
COPYINST MVC   0(0,2),0(3)           EXECUTED INSTRUCTION
COPYDONE DS    0H
  .
*  EXIT CODE
         LA    15,0                  SET RETURN CODE OF 0
         PR                          RETURN TO CALLER
Example 2: Using the MVCL Instruction: The second COPYDATA example uses the MVCL instruction to move the specified data in groups of 1048576 bytes: 
COPYDATA DS    0D
         BAKR  14,0                  SAVE CALLER'S STATUS
         LAE   12,0(0,0)             BASE REG AR
         BALR  12,0                  BASE REG GR
         USING *,12                  ADDRESSABILITY
  .
         LA    6,0(,2)               COPY TARGET ADDRESS
         LA    7,0(,3)               COPY SOURCE ADDRESS
         LTR   8,4                   COPY AND TEST LENGTH
         BNP   COPYDONE              EXIT IF LENGTH NEGATIVE OR ZERO
  .
         LAE   4,0(0,3)              COPY SOURCE AR/GR
         L     9,COPYLEN             GET LENGTH FOR MVCL
         SR    8,9                   SUBTRACT LENGTH OF COPY
         BNP   COPYLAST              IF LENGTH NOW NEGATIVE OR ZERO
*                                    THEN GO COPY LAST PART
  .
COPYLOOP DS    0H
         LR    3,9                   GET TARGET LENGTH FOR MVCL
         LR    5,9                   GET SOURCE LENGTH FOR MVCL
         MVCL  2,4                   COPY DATA
         ALR   6,9                   ADD COPYLEN TO TARGET ADDRESS
         ALR   7,9                   ADD COPYLEN TO SOURCE ADDRESS
         LR    2,6                   COPY NEW TARGET ADDRESS
         LR    4,7                   COPY NEW SOURCE ADDRESS
         SR    8,9                   SUBTRACT COPYLEN FROM LENGTH
         BP    COPYLOOP              IF LENGTH STILL GREATER THAN
*                                    ZERO, THEN LOOP BACK
  .
COPYLAST DS    0H
         AR    8,9                   ADD COPYLEN
         LR    3,8                   COPY TARGET LENGTH FOR MVCL
         LR    5,8                   COPY SOURCE LENGTH FOR MVCL
         MVCL  2,4                   COPY LAST PART OF THE DATA
         B     COPYDONE              BRANCH TO EXIT CODE
COPYLEN  DC    F'1048576'            AMOUNT TO MOVE ON EACH MVCL
COPYDONE DS    0H
  .
*  EXIT CODE
         LA    15,0                  SET RETURN CODE OF 0
         PR                          RETURN TO CALLER
Programming Notes for Example 2:
Parent topic: Creating and using data spaces