Datasheet

The C and C++ Libraries

4.12 Selecting real-time division

The division helper routine supplied with the ARM libraries provides good overall

performance. However, the amount of time required to perform a division depends on

the input values. A 4-bit quotient requires only 12 cycles, but a 32-bit quotient requires

96 cycles. Some applications require a faster worst-case cycle count at the expense of

lower average performance. For this reason, two divide routines are provided with the

ARM library.

The real-time routine:

• always executes in fewer than 45 cycles

• is faster than the standard division helper routine for larger quotients

• is slower than the standard division helper routine for typical quotients

• returns the same results

• calls the same error reporting mechanism on a division by zero

• does not require any change in the surrounding code.

Select the real-time divide routine, instead of the generally more efficient routine, by

using either:

•

IMPORT __use_realtime_division

from assembly language

•

#pragma import(__use_realtime_division)

from C.

Note

Because it uses the CLZ instruction and the DSP multiplies, the real-time division

routine only works on ARM architecture v5TE and above. If you reference

__use_realtime_division

and compile and link for a core that does not support these, the

linker displays an error similar to:

Error: L6218E: Undefined symbol

__realtime_division_only_works_on_architecture_5E__

(referred from myobj.o)