ARM Compiler toolchain v4.1 for µVision Using the Compiler

Compiler Coding Practices
5.42 Example of hardware and software support differences for floating-point
arithmetic
Example 5-2 shows a function implementing floating-point arithmetic in C code.
Example 5-2 Floating-point arithmetic implemented in C code
float foo(float num1, float num2)
{
float temp, temp2;
temp = num1 + num2;
temp2 = num2 * num2;
return temp2 - temp;
}
When the C code of Example 5-2 is compiled with the command-line options --cpu 5TE and
--fpu softvfp, the compiler produces machine code with the disassembly shown in
Example 5-3. In Example 5-3, floating-point arithmetic is performed in software through calls
to library routines such as __aeabi_fmul.
Example 5-3 Support for floating-point arithmetic in software
||foo|| PROC
PUSH
MOV
BL
MOV
MOV
MOV
BL
MOV
POP
B
ENDP
{r4-r6, lr}
r4, r1
__aeabi_fadd
r5, r0
r1, r4
r0, r4
__aeabi_fmul
r1, r5
{r4-r6, lr}
__aeabi_fsub
However, when the C code of Example 5-2 is compiled with the command-line option --fpu
vfp, the compiler produces machine code with the disassembly shown in Example 5-4. In
Example 5-4, floating-point arithmetic is performed in hardware through floating-point
arithmetic instructions such as VMUL.F32.
Example 5-4 Support for floating-point arithmetic in hardware
||foo|| PROC
VADD.F32 s2, s0, s1
VMUL.F32 s0, s1, s1
VSUB.F32 s0, s0, s2
BX lr
ENDP
5.42.1 See also
Concepts
• Default selection of hardware or software floating-point support on page 5-55
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