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      1 /* ===-- floatundidf.c - Implement __floatundidf ---------------------------===
      2  *
      3  *                     The LLVM Compiler Infrastructure
      4  *
      5  * This file is dual licensed under the MIT and the University of Illinois Open
      6  * Source Licenses. See LICENSE.TXT for details.
      7  *
      8  * ===----------------------------------------------------------------------===
      9  *
     10  * This file implements __floatundidf for the compiler_rt library.
     11  *
     12  * ===----------------------------------------------------------------------===
     13  */
     14 
     15 /* Returns: convert a to a double, rounding toward even. */
     16 
     17 /* Assumption: double is a IEEE 64 bit floating point type
     18  *             du_int is a 64 bit integral type
     19  */
     20 
     21 /* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */
     22 
     23 #include "int_lib.h"
     24 
     25 #ifndef __SOFT_FP__
     26 /* Support for systems that have hardware floating-point; we'll set the inexact flag
     27  * as a side-effect of this computation.
     28  */
     29 
     30 COMPILER_RT_ABI double
     31 __floatundidf(du_int a)
     32 {
     33 	static const double twop52 = 4503599627370496.0; // 0x1.0p52
     34 	static const double twop84 = 19342813113834066795298816.0; // 0x1.0p84
     35 	static const double twop84_plus_twop52 = 19342813118337666422669312.0; // 0x1.00000001p84
     36 
     37 	union { uint64_t x; double d; } high = { .d = twop84 };
     38 	union { uint64_t x; double d; } low = { .d = twop52 };
     39 
     40 	high.x |= a >> 32;
     41 	low.x |= a & UINT64_C(0x00000000ffffffff);
     42 
     43 	const double result = (high.d - twop84_plus_twop52) + low.d;
     44 	return result;
     45 }
     46 
     47 #else
     48 /* Support for systems that don't have hardware floating-point; there are no flags to
     49  * set, and we don't want to code-gen to an unknown soft-float implementation.
     50  */
     51 
     52 COMPILER_RT_ABI double
     53 __floatundidf(du_int a)
     54 {
     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     {
     62         /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
     63          *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
     64          *                                                12345678901234567890123456
     65          *  1 = msb 1 bit
     66          *  P = bit DBL_MANT_DIG-1 bits to the right of 1
     67          *  Q = bit DBL_MANT_DIG bits to the right of 1
     68          *  R = "or" of all bits to the right of Q
     69          */
     70         switch (sd)
     71         {
     72         case DBL_MANT_DIG + 1:
     73             a <<= 1;
     74             break;
     75         case DBL_MANT_DIG + 2:
     76             break;
     77         default:
     78             a = (a >> (sd - (DBL_MANT_DIG+2))) |
     79                 ((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0);
     80         };
     81         /* finish: */
     82         a |= (a & 4) != 0;  /* Or P into R */
     83         ++a;  /* round - this step may add a significant bit */
     84         a >>= 2;  /* dump Q and R */
     85         /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */
     86         if (a & ((du_int)1 << DBL_MANT_DIG))
     87         {
     88             a >>= 1;
     89             ++e;
     90         }
     91         /* a is now rounded to DBL_MANT_DIG bits */
     92     }
     93     else
     94     {
     95         a <<= (DBL_MANT_DIG - sd);
     96         /* a is now rounded to DBL_MANT_DIG bits */
     97     }
     98     double_bits fb;
     99     fb.u.s.high = ((e + 1023) << 20)      |        /* exponent */
    100                 ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */
    101     fb.u.s.low = (su_int)a;                         /* mantissa-low  */
    102     return fb.f;
    103 }
    104 #endif
    105 
    106 #if defined(__ARM_EABI__)
    107 #if defined(COMPILER_RT_ARMHF_TARGET)
    108 AEABI_RTABI double __aeabi_ul2d(du_int a) {
    109   return __floatundidf(a);
    110 }
    111 #else
    112 AEABI_RTABI double __aeabi_ul2d(du_int a) COMPILER_RT_ALIAS(__floatundidf);
    113 #endif
    114 #endif
    115