Conditionally branches to an address contained in the Link Register.
| PowerPC | |
|---|---|
| bclr | BO,BI |
| bclrl | BO,BI |
| POWER | |
|---|---|
| bcr | BO,BI |
| bcrl | BO,BI |
See "Extended Mnemonics of Branch Instructions" for more information.
The bclr and bcr instructions branch to an instruction specified by the branch target address. The branch target address is the concatenation of bits 0-29 of the Link Register and b'00'.
The bclr and bcr instructions have two syntax forms. Each syntax form has a different effect on the Link bit and Link Register.
| Syntax Form | Absolute Address Bit (AA) | Fixed-Point Exception Register | Link Bit (LK) | Condition Register Field 0 |
| bclr | None | None | 0 | None |
| bclrl | None | None | 1 | None |
| bcr | None | None | 0 | None |
| bcrl | None | None | 1 | None |
The two syntax forms of the bclr and bcr instruction never affect the Fixed-Point Exception Register or Condition Register Field 0. If the Link bit (LK) is 1, then the effective address of the instruction that follows the branch instruction is placed into the Link Register.
The Branch Option field (BO) is used to combine different types of branches into a single instruction. Extended mnemonics are provided to set the Branch Option field automatically.
The encoding for the BO field is defined in PowerPC Architecture. The following list gives brief descriptions of the possible values for this field:
In the PowerPC Architecture, the z bit denotes a bit that must be 0. If the bit is not 0, the instruction form is invalid.
In the PowerPC Architecture, the y bit provides a hint about whether a conditional branch is likely to be taken. The value of this bit can be either 0 or 1. The default value is 0.
In the POWER Architecture, the z and y bits can be either 0 or 1.
| BO | Specifies Branch Option field. |
| BI | Specifies bit in Condition Register for condition comparison. |
The following code branches to the calculated branch target address dependent on bit 0 of the Condition Register:
bclr 0x0,0 # The Count Register is decremented. # A branch occurs if the LT bit is set to zero in the # Condition Register and if the Count Register # does not equal zero. # If the conditions are met, the instruction branches to # the concatenation of bits 0-29 of the Link Register and b'00'.