mp_set_double.c

   1 #include "tommath_private.h"
   2 #ifdef MP_SET_DOUBLE_C
   3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
   4 /* SPDX-License-Identifier: Unlicense */
   5
   6 #if defined(MP_HAS_SET_DOUBLE)
   7 mp_err mp_set_double(mp_int *a, double b)
   8 {
   9    uint64_t frac;
  10    int exp;
  11    mp_err err;
  12    union {
  13       double   dbl;
  14       uint64_t bits;
  15    } cast;
  16    cast.dbl = b;
  17
  18    exp = (int)((unsigned)(cast.bits >> 52) & 0x7FFu);
  19    frac = (cast.bits & (((uint64_t)1 << 52) - (uint64_t)1)) | ((uint64_t)1 << 52);
  20
  21    if (exp == 0x7FF) { /* +-inf, NaN */
  22       return MP_VAL;
  23    }
  24    exp -= 1023 + 52;
  25
  26    mp_set_u64(a, frac);
  27
  28    err = (exp < 0) ? mp_div_2d(a, -exp, a, NULL) : mp_mul_2d(a, exp, a);
  29    if (err != MP_OKAY) {
  30       return err;
  31    }
  32
  33    if (((cast.bits >> 63) != 0u) && !mp_iszero(a)) {
  34       a->sign = MP_NEG;
  35    }
  36
  37    return MP_OKAY;
  38 }
  39 #else
  40 /* pragma message() not supported by several compilers (in mostly older but still used versions) */
  41 #  ifdef _MSC_VER
  42 #    pragma message("mp_set_double implementation is only available on platforms with IEEE754 floating point format")
  43 #  else
  44 #    warning "mp_set_double implementation is only available on platforms with IEEE754 floating point format"
  45 #  endif
  46 #endif
  47 #endif