/* SPDX-License-Identifier: GPL-2.0 */

  #ifndef _LINUX_RECIPROCAL_DIV_H
  #define _LINUX_RECIPROCAL_DIV_H
  
  #include <linux/types.h>
  
  /*

   * This algorithm is based on the paper "Division by Invariant
   * Integers Using Multiplication" by Torbjörn Granlund and Peter
   * L. Montgomery.

   *

   * The assembler implementation from Agner Fog, which this code is
   * based on, can be found here:
   * http://www.agner.org/optimize/asmlib.zip

   *

   * This optimization for A/B is helpful if the divisor B is mostly
   * runtime invariant. The reciprocal of B is calculated in the
   * slow-path with reciprocal_value(). The fast-path can then just use
   * a much faster multiplication operation with a variable dividend A
   * to calculate the division A/B.

   */

  struct reciprocal_value {
  	u32 m;
  	u8 sh1, sh2;
  };

  struct reciprocal_value reciprocal_value(u32 d);

  static inline u32 reciprocal_divide(u32 a, struct reciprocal_value R)

  {

  	u32 t = (u32)(((u64)a * R.m) >> 32);
  	return (t + ((a - t) >> R.sh1)) >> R.sh2;

  }

  
  #endif /* _LINUX_RECIPROCAL_DIV_H */