Package xyz.cofe.trambda.bc.mth

Class MLookupSwitchInsn

  • All Implemented Interfaces:
    Serializable, xyz.cofe.collection.ImTree<ByteCode>, xyz.cofe.collection.ImTreeWalk<ByteCode>, ByteCode, MethodByteCode, MethodWriter
    public class MLookupSwitchInsn
extends MAbstractBC
implements MethodWriter
    lookupswitch

    Operation

    Access jump table by key match and jump

    Format

     lookupswitch
 <0-3 byte pad>
 defaultbyte1
 defaultbyte2
 defaultbyte3
 defaultbyte4
 npairs1
 npairs2
 npairs3
 npairs4
 match-offset pairs...

    Forms

    lookupswitch = 171 (0xab)

    Operand Stack

    ..., key → ...

    Description

    A lookupswitch is a variable-length instruction. Immediately after the lookupswitch opcode, between zero and three bytes must act as padding, such that defaultbyte1 begins at an address that is a multiple of four bytes from the start of the current method (the opcode of its first instruction). Immediately after the padding follow a series of signed 32-bit values: default, npairs, and then npairs pairs of signed 32-bit values. The npairs must be greater than or equal to 0. Each of the npairs pairs consists of an int match and a signed 32-bit offset. Each of these signed 32-bit values is constructed from four unsigned bytes as (byte1 << 24) | (byte2 << 16) | (byte3 << 8) | byte4.

    The table match-offset pairs of the lookupswitch instruction must be sorted in increasing numerical order by match.

    The key must be of type int and is popped from the operand stack. The key is compared against the match values. If it is equal to one of them, then a target address is calculated by adding the corresponding offset to the address of the opcode of this lookupswitch instruction. If the key does not match any of the match values, the target address is calculated by adding default to the address of the opcode of this lookupswitch instruction. Execution then continues at the target address.

    The target address that can be calculated from the offset of each match-offset pair, as well as the one calculated from default, must be the address of an opcode of an instruction within the method that contains this lookupswitch instruction.

    Notes

    The alignment required of the 4-byte operands of the lookupswitch instruction guarantees 4-byte alignment of those operands if and only if the method that contains the lookupswitch is positioned on a 4-byte boundary.

    The match-offset pairs are sorted to support lookup routines that are quicker than linear search.

    See Also:
    Serialized Form

    • Constructor Detail

      • MLookupSwitchInsn

        public MLookupSwitchInsn()

      • MLookupSwitchInsn

        public MLookupSwitchInsn​(String defHdl,
                         int[] keys,
                         String[] labels)