HLASM - MVCL = MoVe Characters Long

The opcode of the MVCL instruction is X'0E'.

Usage

Move data fields longer than 256 bytes.
Wipe an area of storage.

Arguments

Even-odd register pair containing destination field and length:
- Destination address in the even register.
- Destination field length in the low-order 24 bits of the odd 32-bit register.
Even-odd register pair containing source field, length and padding value:
- Source address in the even register.
- Source field length in the low-order 24 bits of the odd 32-bit register.
- Pad value in the high-order 8 bits of the odd 32-bit register.

Function

The processor moves the data from the source to the destination field, padding it with the pad character if the destination field is longer.
The processor sets the condition code as follows:
- 0 = Lengths are equal.
- 1 = Data truncated.
- 2 = Data padded.
- 3 = No data moved; fields overlap destructively.

Special Cases

If the source length is specified as 0, then the entire destination field will be filled with the pad character.

Related Instructions

MVC moves fields up to 256 bytes (inclusive) without padding.
MVCLE moves fields longer than 16M bytes.

Hardware

The MVCL instruction was not in the original instruction set, but has been around for a very long time.

Remarks

The PSW's Amode setting determines how many bits are used for the source and destination addresses.
MVCL is an interruptible instruction. That is, its execution can be interrupted and later resumed by the operating system. To the programmer this is a transparent process, but in dumps intermediate results may show up. This happens because the processor will adjust the contents of the four registers according to the progress made.
After MVCL completes the contents of the four input registers are destroyed.

Examples

         YREGS                          * Define register names
         ...
         L     R0,TABLE                 * Point to field
         L     R1,TABLE_END             * Point end of field
         SR    R1,R0                    * Obtain length
         XR    R14,R14                  * No source data
         XR    R15,R15                  * Length = 0, Pad = X'00'
         MVCL  R0,R14                   * Wipe entire table
         ...

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