RM0004 Datasheet, PDF (1110/1176 Pages) STMicroelectronics – Programmer’s reference manual for Book E processors

RM0004
Simplified mnemonics for PowerPC instructions
Appendix B Simplified mnemonics for PowerPC
instructions
This chapter describes simplified mnemonics, which are provided for easier coding of
assembly language programs. Simplified mnemonics are defined for the most frequently
used forms of branch conditional, compare, trap, rotate and shift, and certain other
instructions defined by the PowerPC™ architecture and by implementations of and
extensions to the PowerPC architecture.
Chapter B.11: Comprehensive list of simplified mnemonics on page 1133,” provides an
alphabetical listing of simplified mnemonics. Some assemblers may define additional
simplified mnemonics not included here. The simplified mnemonics listed here should be
supported by all compilers.
B.1
Overview
Simplified (or extended) mnemonics allow an assembly-language programmer to program
using more intuitive mnemonics and symbols than the instructions and syntax defined by the
instruction set architecture. For example, to code the conditional call “branch to an absolute
target if CR4 specifies a greater than condition, setting the LR without simplified
mnemonics, the programmer would write the branch conditional instruction, bc 12,17,target.
The simplified mnemonic, branch if greater than, bgt cr4, target, incorporates the
conditions. Not only is it easier to remember the symbols than the numbers when
programming, it is also easier to interpret simplified mnemonics when reading existing code.
Although the original PowerPC architecture documents include a set of simplified
mnemonics, these are not a formal part of the architecture, but rather a recommendation for
assemblers that support the instruction set.
Many simplified mnemonics have been added to those originally included in the architecture
documentation. Some assemblers created their own, and others have been added to
support extensions to the instruction set (for example, AltiVec instructions and Book E
auxiliary processing units (APUs)). Simplified mnemonics have been added for new
architecturally defined and new implementation-specific special-purpose registers (SPRs).
These simplified mnemonics are described only in a very general way.
B.2
B.2.1
Subtract simplified mnemonics
This section describes simplified mnemonics for subtract instructions.
Subtract immediate
There is no subtract immediate instruction, however, its effect is achieved by negating the
immediate operand of an Add Immediate instruction, addi. Simplified mnemonics include
this negation, making the intent of the computation more clear. These are listed in
Table 275.
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