kc3-lang/libtommath/mp_is_square.c

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• Hash : ab7bcec5
  Author :
  Date : 2021-12-13T21:08:49
  

  Introduced 0 (zero) to mp_is_square as a perfect square

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• mp_is_square.c

• #include "tommath_private.h"
  #ifdef MP_IS_SQUARE_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  /* Check if remainders are possible squares - fast exclude non-squares */
  static const char rem_128[128] = {
     0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
     0, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
     1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
     1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
     0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
     1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
     1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
     1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1
  };
  
  static const char rem_105[105] = {
     0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1,
     0, 0, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1,
     0, 1, 1, 1, 1, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1,
     1, 0, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1,
     0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1,
     1, 1, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1, 1, 1, 1,
     1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1
  };
  
  /* Store non-zero to ret if arg is square, and zero if not */
  mp_err mp_is_square(const mp_int *arg, bool *ret)
  {
     mp_err   err;
     mp_digit c;
     mp_int   t;
     uint32_t r;
  
     /* Default to Non-square :) */
     *ret = false;
  
     if (mp_isneg(arg)) {
        return MP_VAL;
     }
  
     if (mp_iszero(arg)) {
        *ret = true;
        return MP_OKAY;
     }
  
     /* First check mod 128 (suppose that MP_DIGIT_BIT is at least 7) */
     if (rem_128[127u & arg->dp[0]] == (char)1) {
        return MP_OKAY;
     }
  
     /* Next check mod 105 (3*5*7) */
     if ((err = mp_mod_d(arg, 105uL, &c)) != MP_OKAY) {
        return err;
     }
     if (rem_105[c] == (char)1) {
        return MP_OKAY;
     }
  
  
     if ((err = mp_init_u32(&t, 11u*13u*17u*19u*23u*29u*31u)) != MP_OKAY) {
        return err;
     }
     if ((err = mp_mod(arg, &t, &t)) != MP_OKAY) {
        goto LBL_ERR;
     }
     r = mp_get_u32(&t);
     /* Check for other prime modules, note it's not an ERROR but we must
      * free "t" so the easiest way is to goto LBL_ERR.  We know that err
      * is already equal to MP_OKAY from the mp_mod call
      */
     if (((1uL<<(r%11uL)) & 0x5C4uL) != 0uL)         goto LBL_ERR;
     if (((1uL<<(r%13uL)) & 0x9E4uL) != 0uL)         goto LBL_ERR;
     if (((1uL<<(r%17uL)) & 0x5CE8uL) != 0uL)        goto LBL_ERR;
     if (((1uL<<(r%19uL)) & 0x4F50CuL) != 0uL)       goto LBL_ERR;
     if (((1uL<<(r%23uL)) & 0x7ACCA0uL) != 0uL)      goto LBL_ERR;
     if (((1uL<<(r%29uL)) & 0xC2EDD0CuL) != 0uL)     goto LBL_ERR;
     if (((1uL<<(r%31uL)) & 0x6DE2B848uL) != 0uL)    goto LBL_ERR;
  
     /* Final check - is sqr(sqrt(arg)) == arg ? */
     if ((err = mp_sqrt(arg, &t)) != MP_OKAY) {
        goto LBL_ERR;
     }
     if ((err = mp_sqr(&t, &t)) != MP_OKAY) {
        goto LBL_ERR;
     }
  
     *ret = (mp_cmp_mag(&t, arg) == MP_EQ);
  LBL_ERR:
     mp_clear(&t);
     return err;
  }
  #endif
  

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