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Branch Mnemonics

The PowerPC processor family supports a rich variety of extended mnemonics for its three conditional branch operators: bc , bclr , and bcctr . Normally, the condition and the nature of the branch are specified by numeric operands, but with the extended mnemonics, these numeric operands are determined by the assembler from the mnemonic used.

Conditional branches can alter the contents of the Count Register ( ctr ), and can take effect based on the resulting value in the Count Register, and on whether a specified condition is true or false. The first table below summarizes the extended mnemonics for branches that affect the Count Register, while the second summarizes additional mnemonics for branches on true and false conditions that don't affect the Count Register. The effect of the branch is given on the left. The first four columns of each table are for branches where the Link Register bit in the instruction is clear (not set); the remaining columns are for branches where the Link Register bit in the instruction is set. Each set of four columns gives mnemonics for relative and absolute branches, and for branches to the Link Register or the Count Register.

Branch Type	LR not set				LR set
	bc	bca	bclr	bcctr	bcl	bcla	bclrl	bcctrl
	Rel.	Abs.	to LR	to CTR	Rel.	Abs.	to LR	to CTR
unconditional	b	ba	blr	bctr	bl	bla	blrl	bctrl
if condition true	bt	bta	btlr	btctr	btl	btla	btlrl	btctrl
if condition false	bf	bfa	bflr	bfctr	bfl	bfla	bflrl	bfctrl
decrement CTR, branch if CTR non-zero	bdnz	bdnza	bdnzlr	-	bdnzl	bdnzla	bdnzlrl	-
Decrement CTR, branch if CTR non-zero and condition true	bdnzt	bdnzta	bdnztlr	-	bdnztl	bdnztla	bdnztlrl	-
Decrement CTR, branch if CTR non-zero and condition false	bdnzf	bdnzfa	bdnzflr	-	bdnzfl	bdnzfla	bdnzflrl	-
Decrement CTR, branch if CTR zero	bdz	bdza	bdzlr	-	bdzl	bdzla	bdzlrl	-
Decrement CTR, branch if CTR zero and condition true	bdzt	bdzta	bdztlr	-	bdztl	bdztla	bdztlrl	-
Decrement CTR, branch if CTR zero and condition false	bdzf	bdzfa	bdzflr	-	bdzfl	bdzfla	bdzflrl	-

The mnemonics in the table above encode specific values for the BO field of the non-extended operators. The BO field controls the effect on the Count Register and on what type of condition the branch is to be taken. The BI field, which controls the specific condition to consider, must still be given, as the first operand. The value of this operand indicates which field of the Condition Register to use, and which bit within that field to consider.

The Condition Register has 8 fields, numbered 0 to 7, each of which contains a bit for conditions less than , greater than , equal , and summary overflow or unordered . The numeric value for field n of the Condition Register is 4* n , and the numeric values for the conditions are 0, 1, 2, and 3, respectively. The following symbols may be used instead of numbers:

Symbol	Value	Meaning
lt	0	Less than
gt	1	Greater than
eq	2	Equal
so	3	Summary overflow
un	3	Unordered (after floating-point comparison)
cr0	0	Condition Register field 0
cr1	4	Condition Register field 1
cr2	8	Condition Register field 2
cr3	12	Condition Register field 3
cr4	16	Condition Register field 4
cr5	20	Condition Register field 5
cr6	24	Condition Register field 6
cr7	28	Condition Register field 7

For example, a branch if condition true for the condition greater than in Condition Register field 3 could be written in any of these ways:

bt cr3+gt,target bt 12+1,target bt 13,target

Omitting the symbol for either the Condition Register field or the condition is permitted, as long as the result of the expression is a number from 0-31:

bt gt,target ; uses field 0 bt cr3,target ; branches on less than in field 3 bt 13,target ; branches on less than in field 3

Another way to specify these conditions is to use the extended mnemonics in the second table, below. These mnemonics encode the actual condition on which to take a branch. The second and third letters of the mnemonic indicate that condition:

Code	Meaning
lt	Less than
le	Less than or equal
eq	Equal
ge	Greater than or equal
gt	Greater than
nl	Not less than
ne	Not equal
ng	Not greater than
so	Summary overflow
ns	Not summary overflow
uo	Unordered (after floating-point comparison)
nu	Not unordered (after floating-point comparison)

Some condition codes, such as le , are actually more compact codes for a false result on the opposite condition in the set of conditions given previously (for example, le is equivalent to if condition false on condition greater than ).

By default, the extended mnemonics in the table below used Condition Register field 0. An optional first operand can be given to specify another field, in either numeric form or as a symbol of the form cr n . For example:

bgt target ; branch if cr0 shows "greater than" bgt cr3,target ; branch if cr3 shows "greater than"

Branch Type	LR not set				LR set
	bc	bca	bclr	bcctr	bcl	bcla	bclrl	bcctrl
	Rel.	Abs.	to LR	to CTR	Rel.	Abs.	to LR	to CTR
less than	blt	blta	bltlr	bltctr	bltl	bltla	bltlrl	bltctrl
less than or equal	ble	blea	blelr	blectr	blel	blela	blelrl	blectrl
equal	beq	beqa	beqlr	beqctr	beql	beqla	beqlrl	beqctrl
greater than or equal	bge	bgea	bgelr	bgectr	bgel	bgela	bgerl	bgectrl
greater than	bgt	bgta	bgtlr	bgtctr	bgttl	bgla	bgtlrl	bgtctrl
not less than	bnl	bnla	bnllr	bnlctr	bnll	bnlla	bnllrl	bnlctrl
not equal	bne	bnea	bnelr	bnectr	bnel	bnela	bnelrl	bnectrl
not greater than	bng	bnga	bnglr	bngctr	bngl	bngla	bnglrl	bngctrl
summary overflow	bso	bsoa	bsolr	bsoctr	bsol	bsola	bsolrl	bsoctrl
not summary overflow	bns	bnsa	bnslr	bnsctr	bnsl	bnsla	bnslrl	bnsctrl
unordered	bun	buna	bunlr	bunctr	bunl	bunla	bunlrl	bunctrl
not unordered	bnu	bnua	bnulr	bnuctr	bnul	bnula	bnulrl	bnuctrl