mpf_normalize.c

   1 /* LibTomFloat, multiple-precision floating-point library
   2  *
   3  * LibTomFloat is a library that provides multiple-precision
   4  * floating-point artihmetic as well as trigonometric functionality.
   5  *
   6  * This library requires the public domain LibTomMath to be installed.
   7  *
   8  * This library is free for all purposes without any express
   9  * gurantee it works
  10  *
  11  * Tom St Denis, tomstdenis@iahu.ca, http://float.libtomcrypt.org
  12  */
  13 #include <tomfloat.h>
  14
  15 int  mpf_normalize(mp_float *a)
  16 {
  17    long     cb, diff;
  18    int      err;
  19    mp_digit c;
  20
  21    /* sanity */
  22    if (a->radix < 2) {
  23       return MP_VAL;
  24    }
  25
  26    cb = mp_count_bits(&(a->mantissa));
  27    if (cb > a->radix) {
  28       diff    = cb - a->radix;
  29       a->exp += diff;
  30
  31       /* round it, add 1 after shift if diff-1'th bit is 1 */
  32       c = a->mantissa.dp[diff/DIGIT_BIT] & (1U<<(diff%DIGIT_BIT));
  33       if ((err = mp_div_2d(&(a->mantissa), diff, &(a->mantissa), NULL)) != MP_OKAY) {
  34          return err;
  35       }
  36
  37       if (c != 0) {
  38          return mp_add_d(&(a->mantissa), 1, &(a->mantissa));
  39       } else {
  40          return MP_OKAY;
  41       }
  42    } else if (cb < a->radix) {
  43       if (mp_iszero(&(a->mantissa)) == MP_YES) {
  44          return mpf_const_0(a);
  45       } else {
  46          diff    = a->radix - cb;
  47          a->exp -= diff;
  48          return mp_mul_2d(&(a->mantissa), diff, &(a->mantissa));
  49       }
  50    }
  51    return MP_OKAY;
  52 }
  53