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#### 9.40.3.2 Instruction Mnemonics

All instructions documented in the Principles of Operation are supported with the mnemonic and order of operands as described. The instruction mnemonic identifies the instruction format (s390 Formats) and the specific operation code for the instruction. For example, the ‘`lr`’ mnemonic denotes the instruction format ‘`RR`’ with the operation code ‘`0x18`’.

The definition of the various mnemonics follows a scheme, where the first character usually hint at the type of the instruction:

    a
    add instruction, for example ‘al’ for add logical 32-bit
    b
    branch instruction, for example ‘bc’ for branch on condition
    c
    compare or convert instruction, for example ‘cr’ for compare
    register 32-bit
    d
    divide instruction, for example ‘dlr’ devide logical register
    64-bit to 32-bit
    i
    insert instruction, for example ‘ic’ insert character
    l
    load instruction, for example ‘ltr’ load and test register
    mv
    move instruction, for example ‘mvc’ move character
    m
    multiply instruction, for example ‘mh’ multiply halfword
    n
    and instruction, for example ‘ni’ and immediate
    o
    or instruction, for example ‘oc’ or character
    sla, sll
    shift left single instruction
    sra, srl
    shift right single instruction
    st
    store instruction, for example ‘stm’ store multiple
    s
    subtract instruction, for example ‘slr’ subtract
    logical 32-bit
    t
    test or translate instruction, of example ‘tm’ test under mask
    x
    exclusive or instruction, for example ‘xc’ exclusive or
    character

Certain characters at the end of the mnemonic may describe a property of the instruction:

    c
    the instruction uses a 8-bit character operand
    f
    the instruction extends a 32-bit operand to 64 bit
    g
    the operands are treated as 64-bit values
    h
    the operand uses a 16-bit halfword operand
    i
    the instruction uses an immediate operand
    l
    the instruction uses unsigned, logical operands
    m
    the instruction uses a mask or operates on multiple values
    r
    if r is the last character, the instruction operates on registers
    y
    the instruction uses 20-bit displacements

There are many exceptions to the scheme outlined in the above lists, in particular for the privileged instructions. For non-privileged instruction it works quite well, for example the instruction ‘`clgfr`’ c: compare instruction, l: unsigned operands, g: 64-bit operands, f: 32- to 64-bit extension, r: register operands. The instruction compares an 64-bit value in a register with the zero extended 32-bit value from a second register. For a complete list of all mnemonics see appendix B in the Principles of Operation.

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