riscv/mulhi.h


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#ifndef _RISCV_MULHI_H
#define _RISCV_MULHI_H

#include <cstdint>

inline uint64_t mulhu(uint64_t a, uint64_t b)
{
  uint64_t t;
  uint32_t y1, y2, y3;
  uint64_t a0 = (uint32_t)a, a1 = a >> 32;
  uint64_t b0 = (uint32_t)b, b1 = b >> 32;

  t = a1*b0 + ((a0*b0) >> 32);
  y1 = t;
  y2 = t >> 32;

  t = a0*b1 + y1;
  y1 = t;

  t = a1*b1 + y2 + (t >> 32);
  y2 = t;
  y3 = t >> 32;

  return ((uint64_t)y3 << 32) | y2;
}

inline int64_t mulh(int64_t a, int64_t b)
{
  int negate = (a < 0) != (b < 0);
  uint64_t res = mulhu(a < 0 ? -a : a, b < 0 ? -b : b);
  return negate ? ~res + (a * b == 0) : res;
}

inline int64_t mulhsu(int64_t a, uint64_t b)
{
  int negate = a < 0;
  uint64_t res = mulhu(a < 0 ? -a : a, b);
  return negate ? ~res + (a * b == 0) : res;
}

#endif