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      1 /*===-- floatdisf.c - Implement __floatdisf -------------------------------===
      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 __floatdisf for the compiler_rt library.
     11  *
     12  *===----------------------------------------------------------------------===
     13  */
     14 
     15 /* Returns: convert a to a float, rounding toward even.*/
     16 
     17 /* Assumption: float is a IEEE 32 bit floating point type
     18  *             di_int is a 64 bit integral type
     19  */
     20 
     21 /* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */
     22 
     23 #include "int_lib.h"
     24 
     25 ARM_EABI_FNALIAS(l2f, floatdisf)
     26 
     27 COMPILER_RT_ABI float
     28 __floatdisf(di_int a)
     29 {
     30     if (a == 0)
     31         return 0.0F;
     32     const unsigned N = sizeof(di_int) * CHAR_BIT;
     33     const di_int s = a >> (N-1);
     34     a = (a ^ s) - s;
     35     int sd = N - __builtin_clzll(a);  /* number of significant digits */
     36     int e = sd - 1;             /* exponent */
     37     if (sd > FLT_MANT_DIG)
     38     {
     39         /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
     40          *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
     41          *                                                12345678901234567890123456
     42          *  1 = msb 1 bit
     43          *  P = bit FLT_MANT_DIG-1 bits to the right of 1
     44          *  Q = bit FLT_MANT_DIG bits to the right of 1
     45          *  R = "or" of all bits to the right of Q
     46          */
     47         switch (sd)
     48         {
     49         case FLT_MANT_DIG + 1:
     50             a <<= 1;
     51             break;
     52         case FLT_MANT_DIG + 2:
     53             break;
     54         default:
     55             a = ((du_int)a >> (sd - (FLT_MANT_DIG+2))) |
     56                 ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0);
     57         };
     58         /* finish: */
     59         a |= (a & 4) != 0;  /* Or P into R */
     60         ++a;  /* round - this step may add a significant bit */
     61         a >>= 2;  /* dump Q and R */
     62         /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */
     63         if (a & ((du_int)1 << FLT_MANT_DIG))
     64         {
     65             a >>= 1;
     66             ++e;
     67         }
     68         /* a is now rounded to FLT_MANT_DIG bits */
     69     }
     70     else
     71     {
     72         a <<= (FLT_MANT_DIG - sd);
     73         /* a is now rounded to FLT_MANT_DIG bits */
     74     }
     75     float_bits fb;
     76     fb.u = ((su_int)s & 0x80000000) |  /* sign */
     77            ((e + 127) << 23)       |  /* exponent */
     78            ((su_int)a & 0x007FFFFF);   /* mantissa */
     79     return fb.f;
     80 }
     81