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RealView Compiler User's Guide
Preface Introduction Getting started with the ARM Compiler Compiler Features Coding Practices Optimizing code
Optimizing for size versus speed Optimization levels and the debug view Selecting the target device Optimizing loops Using volatile Code metrics Measuring code and data sizes Measuring stack use Reducing debug information in objects and librarie Functions Minimizing parameter passing overhead __value_in_regs __pure Placing ARM function qualifiers Inlining How the compiler decides to inline When is it practical for the compiler to inline? Managing inlining Inlining functions across multiple files Debugging data and the --[no]_inline keyword Marking functions as static Setting breakpoints on inlined functions in ROM im Aligning data About data alignment The __packed qualifier and unaligned accesses to d __packed structures versus individually __packed f Using floating-point arithmetic Support for floating-point operations VFP architectures The --fpu option Floating-point linkage The --fpmode option Using the --fpu option VFP support Trapping and identifying division-by-zero errors Integer division (Software) Floating point division Support for ARM architecture v6 Instruction generation Alignment support Endian support Diagnostic Messages Using the Inline and Embedded Assemblers SemihostingThe --fpu option
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| Home > Coding Practices > Using floating-point arithmetic > The --fpu option | |||
By default, the compiler generates code that makes calls to the software floating-point library fplib in order to carry out floating-point operations. To make use of VFP instructions you must use appropriate compiler options to modify the code generated, as described in Table 4.11.
Table 4.11. VFP compiler options
| Option | Description |
|---|---|
| This is a synonym for |
| Selects hardware vector floating-point unit conforming to architecture VFPv2. |
| Selects hardware vector floating-point unit conforming to architecture VFPv3. VFPv3 is backwards compatible with VFPv2 except that VFPv3 cannot trap floating-point exceptions. |
| Selects the software floating-point library |
| Selects a floating-point library with software floating-point linkage that can use VFPv2 instructions. |
| Selects a floating-point library with software floating-point linkage that uses VFPv3 instructions. |
Note
Selection of a device implies the selection of a particular floating-point unit by default. For example, the option --device DARMP3 implies the option --fpu softvfp.
Any FPU explicitly selected using the --fpu option always overrides any FPU implicitly selected using the --device option. For example, the option --device DARMP3 --fpu=vfpv2 generates code that uses the VFPv2 hardware vector floating-point unit, even though the default for the device DARMP3 is the software floating-point library.
If you specify an FPU explicitly using the --fpu option that is incompatible with the device chosen using the --device option then the compiler generates an error.
Note
The compiler only generates scalar floating-point operations. If you want to use VFP vector operations, then you must do this using assembly code.
For more information about which compiler option to use in a particular set of circumstances see:
‑‑fpu=name in the Compiler Reference Guide.
| Copyright © 2007 ARM Limited. All rights reserved. | ARM DUI 0375A |
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