compiler-rt/lib/builtins/floatundidf.c

   1 //===-- floatundidf.c - Implement __floatundidf ---------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements __floatundidf for the compiler_rt library.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 // Returns: convert a to a double, rounding toward even.
  14
  15 // Assumption: double is a IEEE 64 bit floating point type
  16 //             du_int is a 64 bit integral type
  17
  18 // seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm
  19 // mmmm
  20
  21 #include "int_lib.h"
  22
  23 #ifndef __SOFTFP__
  24 // Support for systems that have hardware floating-point; we'll set the inexact
  25 // flag as a side-effect of this computation.
  26
  27 COMPILER_RT_ABI double __floatundidf(du_int a) {
  28   static const double twop52 = 4503599627370496.0;           // 0x1.0p52
  29   static const double twop84 = 19342813113834066795298816.0; // 0x1.0p84
  30   static const double twop84_plus_twop52 =
  31       19342813118337666422669312.0; // 0x1.00000001p84
  32
  33   union {
  34     uint64_t x;
  35     double d;
  36   } high = {.d = twop84};
  37   union {
  38     uint64_t x;
  39     double d;
  40   } low = {.d = twop52};
  41
  42   high.x |= a >> 32;
  43   low.x |= a & UINT64_C(0x00000000ffffffff);
  44
  45   const double result = (high.d - twop84_plus_twop52) + low.d;
  46   return result;
  47 }
  48
  49 #else
  50 // Support for systems that don't have hardware floating-point; there are no
  51 // flags to set, and we don't want to code-gen to an unknown soft-float
  52 // implementation.
  53
  54 COMPILER_RT_ABI double __floatundidf(du_int a) {
  55   if (a == 0)
  56     return 0.0;
  57   const unsigned N = sizeof(du_int) * CHAR_BIT;
  58   int sd = N - __builtin_clzll(a); // number of significant digits
  59   int e = sd - 1;                  // exponent
  60   if (sd > DBL_MANT_DIG) {
  61     //  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
  62     //  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
  63     //                                                12345678901234567890123456
  64     //  1 = msb 1 bit
  65     //  P = bit DBL_MANT_DIG-1 bits to the right of 1
  66     //  Q = bit DBL_MANT_DIG bits to the right of 1
  67     //  R = "or" of all bits to the right of Q
  68     switch (sd) {
  69     case DBL_MANT_DIG + 1:
  70       a <<= 1;
  71       break;
  72     case DBL_MANT_DIG + 2:
  73       break;
  74     default:
  75       a = (a >> (sd - (DBL_MANT_DIG + 2))) |
  76           ((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG + 2) - sd))) != 0);
  77     };
  78     // finish:
  79     a |= (a & 4) != 0; // Or P into R
  80     ++a;               // round - this step may add a significant bit
  81     a >>= 2;           // dump Q and R
  82     // a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits
  83     if (a & ((du_int)1 << DBL_MANT_DIG)) {
  84       a >>= 1;
  85       ++e;
  86     }
  87     // a is now rounded to DBL_MANT_DIG bits
  88   } else {
  89     a <<= (DBL_MANT_DIG - sd);
  90     // a is now rounded to DBL_MANT_DIG bits
  91   }
  92   double_bits fb;
  93   fb.u.s.high = ((su_int)(e + 1023) << 20) |      // exponent
  94                 ((su_int)(a >> 32) & 0x000FFFFF); // mantissa-high
  95   fb.u.s.low = (su_int)a;                         // mantissa-low
  96   return fb.f;
  97 }
  98 #endif
  99
 100 #if defined(__ARM_EABI__)
 101 #if defined(COMPILER_RT_ARMHF_TARGET)
 102 AEABI_RTABI double __aeabi_ul2d(du_int a) { return __floatundidf(a); }
 103 #else
 104 COMPILER_RT_ALIAS(__floatundidf, __aeabi_ul2d)
 105 #endif
 106 #endif
 107
 108 #if defined(__MINGW32__) && defined(__arm__)
 109 COMPILER_RT_ALIAS(__floatundidf, __u64tod)
 110 #endif