modules/fdlibm/src/s_scalbn.cpp

   1 /*
   2  * Copyright (c) 2005-2020 Rich Felker, et al.
   3  *
   4  * SPDX-License-Identifier: MIT
   5  *
   6  * Please see https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT
   7  * for all contributors to musl.
   8  */
   9 #include <float.h>
  10 #include <stdint.h>
  11
  12 #include "math_private.h"
  13
  14 double scalbn(double x, int n)
  15 {
  16         union {double f; uint64_t i;} u;
  17         double_t y = x;
  18
  19         if (n > 1023) {
  20                 y *= 0x1p1023;
  21                 n -= 1023;
  22                 if (n > 1023) {
  23                         y *= 0x1p1023;
  24                         n -= 1023;
  25                         if (n > 1023)
  26                                 n = 1023;
  27                 }
  28         } else if (n < -1022) {
  29                 /* make sure final n < -53 to avoid double
  30                    rounding in the subnormal range */
  31                 y *= 0x1p-1022 * 0x1p53;
  32                 n += 1022 - 53;
  33                 if (n < -1022) {
  34                         y *= 0x1p-1022 * 0x1p53;
  35                         n += 1022 - 53;
  36                         if (n < -1022)
  37                                 n = -1022;
  38                 }
  39         }
  40         u.i = (uint64_t)(0x3ff+n)<<52;
  41         x = y * u.f;
  42         return x;
  43 }