HLASM - CLCL = Compare Logical Characters Long

The opcode of the CLCL instruction is X'0F'.

Usage

1. Compare nonnumeric data fields longer than 256 bytes.
2. Compare nonnumeric data fields of unequal lengths.

Arguments

1. Even-odd register pair containing first comparand address and length:
   • First comparand address in the even register.
   • First comparand field length in the low-order 24 bits of the 32-bit odd register.
2. Even-odd register pair containing second comparand address, length and padding value:
   • Second comparand address in the even register.
   • Second comparand 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

1. The processor compares the data from both fields. If their lengths are unequal, the shorter field is treated as if it were extended with as many padding characters as needed to make it as long as the other field.
2. The processor sets the condition code as follows:
   • 0 = Operands are equal.
   • 1 = First operand is higher than the second.
   • 2 = First operand is lower than the second.
   • 3 = Not used.

Special Cases

1. If both lengths are 0, then the fields are considered equal.

Related Instructions

1. CLC compares fields up to 256 bytes (inclusive) without padding.
2. CLCLE compares fields longer than 16M bytes.

Hardware

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

Remarks

1. The PSW's Amode setting determines how many bits are used for both comparand field addresses.
2. CLCL 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.
3. After CLCL 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 comapre data required
         XR    R15,R15                  * Length = 0, Pad = X'00'
         CLCL  R0,R14                   * Whole table = X'00' ??
         ...

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