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1.23 Real-time integer division in the ARM libraries

The ARM library provides a real-time division routine and a standard division routine.

The standard division 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. For example, a division that generates a four-bit quotient might require only 12 cycles while a 32-bit quotient might require 96 cycles. Depending on your target, some applications require a faster worst-case cycle count at the expense of lower average performance. For this reason, the ARM library provides two divide routines.

The real-time routine:

  • Always executes in fewer than 45 cycles.

  • Is faster than the standard division routine for larger quotients.

  • Is slower than the standard division routine for typical quotients.

  • Returns the same results.

  • Does not require any change in the surrounding code.

Note

Real-time division is not available in the libraries for Cortex-M1 or Cortex-M0.

Note

The Cortex-R4 and Cortex-M3 processors support hardware floating-point divide, so they do not require the library divide routines.

Select the real-time divide routine using either of the following methods:

  • IMPORT __use_realtime_division from assembly language.

  • asm(".global __use_realtime_division\n") from C.

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