compiler-rt/lib/builtins/floatdidf.c

   1 //===-- floatdidf.c - Implement __floatdidf -------------------------------===//
   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 __floatdidf for the compiler_rt library.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "int_lib.h"
  14
  15 // Returns: convert a to a double, rounding toward even.
  16
  17 // Assumption: double is a IEEE 64 bit floating point type
  18 //             di_int is a 64 bit integral type
  19
  20 // seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm
  21 // mmmm
  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 __floatdidf(di_int a) {
  28   static const double twop52 = 4503599627370496.0; // 0x1.0p52
  29   static const double twop32 = 4294967296.0;       // 0x1.0p32
  30
  31   union {
  32     int64_t x;
  33     double d;
  34   } low = {.d = twop52};
  35
  36   const double high = (int32_t)(a >> 32) * twop32;
  37   low.x |= a & INT64_C(0x00000000ffffffff);
  38
  39   const double result = (high - twop52) + low.d;
  40   return result;
  41 }
  42
  43 #else
  44 // Support for systems that don't have hardware floating-point; there are no
  45 // flags to set, and we don't want to code-gen to an unknown soft-float
  46 // implementation.
  47
  48 COMPILER_RT_ABI double __floatdidf(di_int a) {
  49   if (a == 0)
  50     return 0.0;
  51   const unsigned N = sizeof(di_int) * CHAR_BIT;
  52   const di_int s = a >> (N - 1);
  53   a = (a ^ s) - s;
  54   int sd = N - __builtin_clzll(a); // number of significant digits
  55   int e = sd - 1;                  // exponent
  56   if (sd > DBL_MANT_DIG) {
  57     //  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
  58     //  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
  59     //                                                12345678901234567890123456
  60     //  1 = msb 1 bit
  61     //  P = bit DBL_MANT_DIG-1 bits to the right of 1
  62     // Q = bit DBL_MANT_DIG bits to the right of 1
  63     //  R = "or" of all bits to the right of Q
  64     switch (sd) {
  65     case DBL_MANT_DIG + 1:
  66       a <<= 1;
  67       break;
  68     case DBL_MANT_DIG + 2:
  69       break;
  70     default:
  71       a = ((du_int)a >> (sd - (DBL_MANT_DIG + 2))) |
  72           ((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG + 2) - sd))) != 0);
  73     };
  74     // finish:
  75     a |= (a & 4) != 0; // Or P into R
  76     ++a;               // round - this step may add a significant bit
  77     a >>= 2;           // dump Q and R
  78     // a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits
  79     if (a & ((du_int)1 << DBL_MANT_DIG)) {
  80       a >>= 1;
  81       ++e;
  82     }
  83     // a is now rounded to DBL_MANT_DIG bits
  84   } else {
  85     a <<= (DBL_MANT_DIG - sd);
  86     // a is now rounded to DBL_MANT_DIG bits
  87   }
  88   double_bits fb;
  89   fb.u.s.high = ((su_int)s & 0x80000000) |        // sign
  90                 ((su_int)(e + 1023) << 20) |      // exponent
  91                 ((su_int)(a >> 32) & 0x000FFFFF); // mantissa-high
  92   fb.u.s.low = (su_int)a;                         // mantissa-low
  93   return fb.f;
  94 }
  95 #endif
  96
  97 #if defined(__ARM_EABI__)
  98 #if defined(COMPILER_RT_ARMHF_TARGET)
  99 AEABI_RTABI double __aeabi_l2d(di_int a) { return __floatdidf(a); }
 100 #else
 101 COMPILER_RT_ALIAS(__floatdidf, __aeabi_l2d)
 102 #endif
 103 #endif
 104
 105 #if defined(__MINGW32__) && defined(__arm__)
 106 COMPILER_RT_ALIAS(__floatdidf, __i64tod)
 107 #endif