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Compiler options for floating-point linkage and computations

4.51 Compiler options for floating-point linkage and computations

Compiler options determine the type of floating-point linkage and floating-point computations.

By specifying the type of floating-point linkage and floating-point computations you require, you can determine, from the following table, the associated compiler command-line options that are available.

Table 4-13 Compiler options for floating-point linkage and floating-point computations

Linkage Computations    
Hardware FP linkage Software FP linkage Hardware FP coprocessor Software FP library (fplib) Compiler options
No Yes No Yes
--fpu=softvfp
--apcs=/softfp
No Yes Yes No
--fpu=softvfp+vfpv2
--fpu=softvfp+vfpv3
--fpu=softvfp+vfpv3_fp16
--fpu=softvfp+vfpv3_d16
--fpu=softvfp+vfp3_d16_fp16
--fpu=softvfp+vfpv4
--fpu=softvfp+vfpv4_d16
--fpu=softvfp+fpv4-sp
--apcs=/softfp
Yes No Yes No
--fpu=vfp
--fpu=vfpv2
--fpu=vfpv3
--fpu=vfpv3_fp16
--fpu=vfpv3_dp16
--fpu=vfpv3_d16_fp16
--fpu=vpfv4
--fpu=vfpv4_d16
--fpu=fpv4-sp
--apcs=/hardfp
softvfp specifies software floating-point linkage. When software floating-point linkage is used, either:
  • The calling function and the called function must be compiled using one of the options --softvfp, --fpu softvfp+vfpv2, --fpu softvfp+vfpv3, --fpu softvfp+vfpv3_fp16, softvfp+vfpv3_d16, softvfp+vfpv3_d16_fp16, softvfp+vfpv4, softvfp+vfpv4_d16, or softvfp+fpv4-sp.
  • The calling function and the called function must be declared using the __softfp keyword.
Each of the options --fpu softvfp, --fpu softvfp+vfpv2,--fpu softvfp+vfpv3, --fpu softvfp+vfpv3_fp16, --fpu softvfpv3_d16, --fpu softvfpv3_d16_fp16, --fpu softvfp+vfpv4, softvfp+vfpv4_d16 and softvfp+fpv4-sp specify software floating-point linkage across the whole file. In contrast, the __softfp keyword enables software floating-point linkage to be specified on a function by function basis.

Note

Rather than having separate compiler options to select the type of floating-point linkage you require and the type of floating-point computations you require, you use one compiler option, --fpu, to select both. For example, --fpu=softvfp+vfpv2 selects software floating-point linkage, and a hardware coprocessor for the computations. Whenever you use softvfp, you are specifying software floating-point linkage.
If you use the --fpu option, you must know the VFP architecture version implemented in the target processor. An alternative to --fpu=softvfp+... is --apcs=/softfp. This gives software linkage with whatever VFP architecture version is implied by --cpu. --apcs=/softfp and --apcs=/hardfp are alternative ways of requesting the integer or floating-point variant of the Procedure Call Standard for the ARM Architecture (AAPCS).
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