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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 COMPILER_RT_ABI float
     26 __floatdisf(di_int a)
     27 {
     28     if (a == 0)
     29         return 0.0F;
     30     const unsigned N = sizeof(di_int) * CHAR_BIT;
     31     const di_int s = a >> (N-1);
     32     a = (a ^ s) - s;
     33     int sd = N - __builtin_clzll(a);  /* number of significant digits */
     34     int e = sd - 1;             /* exponent */
     35     if (sd > FLT_MANT_DIG)
     36     {
     37         /*  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
     38          *  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
     39          *                                                12345678901234567890123456
     40          *  1 = msb 1 bit
     41          *  P = bit FLT_MANT_DIG-1 bits to the right of 1
     42          *  Q = bit FLT_MANT_DIG bits to the right of 1
     43          *  R = "or" of all bits to the right of Q
     44          */
     45         switch (sd)
     46         {
     47         case FLT_MANT_DIG + 1:
     48             a <<= 1;
     49             break;
     50         case FLT_MANT_DIG + 2:
     51             break;
     52         default:
     53             a = ((du_int)a >> (sd - (FLT_MANT_DIG+2))) |
     54                 ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0);
     55         };
     56         /* finish: */
     57         a |= (a & 4) != 0;  /* Or P into R */
     58         ++a;  /* round - this step may add a significant bit */
     59         a >>= 2;  /* dump Q and R */
     60         /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */
     61         if (a & ((du_int)1 << FLT_MANT_DIG))
     62         {
     63             a >>= 1;
     64             ++e;
     65         }
     66         /* a is now rounded to FLT_MANT_DIG bits */
     67     }
     68     else
     69     {
     70         a <<= (FLT_MANT_DIG - sd);
     71         /* a is now rounded to FLT_MANT_DIG bits */
     72     }
     73     float_bits fb;
     74     fb.u = ((su_int)s & 0x80000000) |  /* sign */
     75            ((e + 127) << 23)       |  /* exponent */
     76            ((su_int)a & 0x007FFFFF);   /* mantissa */
     77     return fb.f;
     78 }
     79 
     80 #if defined(__ARM_EABI__)
     81 #if defined(COMPILER_RT_ARMHF_TARGET)
     82 AEABI_RTABI float __aeabi_l2f(di_int a) {
     83   return __floatdisf(a);
     84 }
     85 #else
     86 AEABI_RTABI float __aeabi_l2f(di_int a) COMPILER_RT_ALIAS(__floatdisf);
     87 #endif
     88 #endif
     89