Branch and Comparison Instructions

The branch instructions transfer control between instructions.

There are instructions to compare a value of type int on the opernad stack to zero in all possible ways and branch on succes. Other conditional branch instructions include comparing a reference on the operand stack to null and comparing values of type int or type reference. All branching instructions have the offset to the instruction to branch to as their operands.

Non-branching comparison instructions are available to compare values of type long, float or double. These instruction push the result of the comparison on the operand stack.

The following instructions are conditional branch instructions used to compile the Java switch statement (the case statement in Pascal). The tableswitch instruction is used when the case values of the switch can be efficiently used as indices into the table of target offsets. When the case values of the switch are sparse, it becomes more efficient to use the lookupswitch instruction. Both instructions only operate on int values; values types float, long and double have to be converted to int first.

• tableswitch. Access jump table by index and jump. Operands: <0-3 byte pad>, defaultbyte1, defaultbyte2, defaultbyte3, defaultbyte4, lowbyte1, lowbyte2, lowbyte3, lowbyte4, highbyte1, highbyte2, highbyte3, highbyte4, jump offsets.... Stack: ..., index ....

• lookupswitch. Access jump table by key match and jump. Operands: <0-3 byte pad>, defaultbyte1, defaultbyte2, defaultbyte3, defaultbyte4, npairs1, npairs2, npairs3, npairs4, match-offset pairs.... Stack: ..., key ....

Besides instructions to jump to and return from a subroutine, there also are the following unconditional branch instructions:

• goto, goto_w. Branch always (normal offset and wide offset). Operands goto: branchbyte1, branchbyte2. Operands goto_w: branchbyte1, branchbyte2, branchbyte3, branchbyte4. No change on the operand stack.