AN2491 Freescale Semiconductor / Motorola, AN2491 Datasheet - Page 14

• Manufacturer Part Number: AN2491
• Description: Simplified Mnemonics for PowerPC Instructions
• Manufacturer: Freescale Semiconductor / Motorola

Branch Instruction Simplified Mnemonics
Branch Instruction Simplified Mnemonics
4.6 Simplified Mnemonics that Incorporate CR Conditions
The mnemonics in Table 18 are variations of the branch-if-condition-true (BO = 12) and
branch-if-condition-false (BO = 4) encodings. Because these instructions do not depend on the CTR, the
true/false conditions specified by BO can be combined with the CR test bit specified by BI to create a
different set of simplified mnemonics that eliminates the BO operand and the portion of the BI operand
(BI[3–4]) that specifies one of the four possible test bits. However, the simplified mnemonic cannot specify
in which of the eight CR fields the test bit falls, so the BI operand is replaced by a crS operand.
The standard codes shown in Table 16 are used for the most common combinations of branch conditions.
Note that for ease of programming, these codes include synonyms; for example, less than or equal (le) and
not greater than (ng) achieve the same result.
Table 17 shows the syntax for simplified branch mnemonics that incorporate CR conditions. Here, crS
replaces a BI operand to specify only a CR field (because the specific CR bit within the field is now part of
the simplified mnemonic. Note that the default is CR0; if no crS is specified, CR0 is used.
14
(Eliminates BO and Replaces BI with crS)
Code
A CR field symbol, cr0–cr7, is used as the first operand after the simplified
mnemonic. If the default, CR0, is used, no crS is necessary,
eq
ge
ne
ng
so
ns
un
nu
gt
nl
le
lt
Less than
Less than or equal (equivalent to ng)
Equal
Greater than or equal (equivalent to nl)
Greater than
Not less than (equivalent to ge)
Not equal
Not greater than (equivalent to le)
Summary overflow
Not summary overflow
Unordered (after floating-point comparison)
Not unordered (after floating-point comparison)
Simplified Mnemonics for PowerPC™ Instructions
Table 16. Standard Coding for Branch Conditions
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Description
NOTE
Equivalent Bit Tested
ng
ge
—
—
—
—
—
—
—
—
nl
le
EQ
EQ
SO
SO
SO
SO
GT
GT
GT
LT
LT
LT
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