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addsub.c

解説を見る。

#include "multiprec.h"
#include <string.h>

inline size_t
ymp_addabs(digit_t *result, const digit_t *lhs, const digit_t *rhs,
           size_t lhs_len, size_t rhs_len)
{
  double_digit_t tmp = 0;
  size_t i;

  for ( i = 0; i < rhs_len; ++i)
    {
      tmp += lhs[i];
      tmp += rhs[i];
      result[i] = LOW_DIGIT(tmp);
      tmp = HIGH_DIGIT(tmp);
    }
  for ( ; i < lhs_len; ++i)
    {
      tmp += lhs[i];
      result[i] = LOW_DIGIT(tmp);
      tmp = HIGH_DIGIT(tmp);
    }
  if (LOW_DIGIT(tmp))
    {
      result[i++] = LOW_DIGIT(tmp);
    }
  return i;
}



inline size_t
ymp_subabs(digit_t *result, const digit_t *lhs, const digit_t *rhs,
           size_t lhs_len, size_t rhs_len)
{
  double_digit_t tmp = 1;
  size_t i;

  for ( i = 0; i < rhs_len; ++i)
    {
      tmp += MULTIPREC_RADIX - 1;
      tmp += lhs[i];
      tmp -= rhs[i];
      result[i] = LOW_DIGIT(tmp);
      tmp = HIGH_DIGIT(tmp);
    }
  for ( ; i < lhs_len; ++i)
    {
      tmp += MULTIPREC_RADIX - 1;
      tmp += lhs[i];
      result[i] = LOW_DIGIT(tmp);
      tmp = HIGH_DIGIT(tmp);
    }
  while (i-- > 0)
    {
      if (result[i]) break;
    }
  return ++i;
}

inline static void
ymp_do_add(mp_ref_t result, mp_cref_t self, mp_cref_t other, int is_add)
{
  if (self->used > other->used)
    {
      if (is_add)
        {
          ymp_reserve(result, self->used+1);
          result->used
            = ymp_addabs(result->digits, self->digits, other->digits,
                         self->used, other->used);
          result->sign = self->sign;
        }
      else
        {
          ymp_reserve(result, self->used);
          result->used
            = ymp_subabs(result->digits, self->digits, other->digits,
                         self->used, other->used);
          result->sign = self->sign;
        }
      return;
    }
  else if (self->used < other->used)
    {
      if (is_add)
        {
          ymp_reserve(result, other->used+1);
          result->used
            = ymp_addabs(result->digits, other->digits, self->digits,
                         other->used, self->used);
          result->sign = self->sign;
        }
      else
        {
          ymp_reserve(result, other->used);
          result->used
            = ymp_subabs(result->digits, other->digits, self->digits,
                         other->used, self->used);
          result->sign = !self->sign;
        }
      return;
    }



  /* self->used == other->used */

  if (is_add)
    {
      ymp_reserve(result, self->used+1);
      result->used
        = ymp_addabs(result->digits, self->digits, other->digits,
                     self->used, other->used);
      result->sign = self->sign;
    }
  else 
    {
      size_t i = self->used;
      while (i-- > 0)
        {
          if ( self->digits[i] > other->digits[i])
            {
              ymp_reserve(result, ++i);
              result->used
                = ymp_subabs(result->digits, self->digits, other->digits,
                             i, i);
              result->sign = self->sign;
              return;
            }
          else if (self->digits[i] < other->digits[i])
            {
              ymp_reserve(result, ++i);
              result->used
                = ymp_subabs(result->digits, other->digits, self->digits,
                             i, i);
              result->sign = !self->sign;
              return;
            }
        }
      result->sign = positive_sign;
      result->used = 0;
    }
}



inline static void
ymp_do_add_digit(mp_ref_t result, mp_cref_t self, digit_t other, int is_add)
{
  switch (self->used)
    {
    case 0:
      ymp_reserve(result, 1);
      result->sign = self->sign;
      result->used = 1;
      result->digits[0] = other;
      return;

    case 1:
      if (is_add)
        {
          double_digit_t tmp;

          ymp_reserve(result, 2);
          result->sign = self->sign;
          result->used = 1;

          tmp = other;
          tmp += self->digits[0];

          result->digits[0] = LOW_DIGIT(tmp);
          if ( (tmp = HIGH_DIGIT(tmp)) )
            {
              self->digits[1] = LOW_DIGIT(tmp);
              ++result->used;
            }
          return;
        }
      else
        {
          ymp_reserve(result, 1);
          result->used = 1;
          if (self->digits[0] > other)
            {
              result->sign = self->sign;
              result->digits[0] = self->digits[0] - other;
            }
          else
            {
              result->sign = !self->sign;
              self->digits[0] = other - self->digits[0];
            }
          return;
        }
    default:
      if (is_add)
        {
          ymp_reserve(result, self->used+1);
          result->used 
            = ymp_addabs(result->digits, self->digits, &other, self->used, 1);
          result->sign = self->sign;
          return;
        }
      else
        {
          ymp_reserve(result, self->used+1);
          result->used
            = ymp_subabs(result->digits, self->digits, &other, self->used, 1);
          result->sign = self->sign;
          return;
        }
    }
}





void ymp_add(mp_ref_t result, mp_cref_t self, mp_cref_t other)
{
  ymp_do_add(result, self, other, self->sign==other->sign);
}

void ymp_sub(mp_ref_t result, mp_cref_t self, mp_cref_t other)
{
  ymp_do_add(result, self, other, self->sign!=other->sign);
}



void
ymp_add_digit(mp_ref_t result, mp_cref_t self, digit_t val)
{
  ymp_do_add_digit(result, self, val, self->sign==positive_sign);
}

void 
ymp_sub_digit(mp_ref_t result, mp_cref_t self, digit_t val)
{
  ymp_do_add_digit(result, self, val, self->sign!=positive_sign);
}


void ymp_neg(mp_ref_t result, mp_cref_t orig)
{
  result->sign = !orig->sign;
  if (result != orig)
    {
      ymp_reserve(result, orig->used);
      result->used = orig->used;
      memcpy(result->digits, orig->digits, sizeof(digit_t)*orig->used);
    }
}

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