compiler-rt/lib/builtins/floatundisf.c

   1 //===-- floatundisf.c - Implement __floatundisf ---------------------------===//
   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 __floatundisf for the compiler_rt library.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 // Returns: convert a to a float, rounding toward even.
  14
  15 // Assumption: float is a IEEE 32 bit floating point type
  16 //            du_int is a 64 bit integral type
  17
  18 // seee eeee emmm mmmm mmmm mmmm mmmm mmmm
  19
  20 #include "int_lib.h"
  21
  22 COMPILER_RT_ABI float __floatundisf(du_int a) {
  23   if (a == 0)
  24     return 0.0F;
  25   const unsigned N = sizeof(du_int) * CHAR_BIT;
  26   int sd = N - __builtin_clzll(a); // number of significant digits
  27   si_int e = sd - 1;               // 8 exponent
  28   if (sd > FLT_MANT_DIG) {
  29     //  start:  0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx
  30     //  finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR
  31     //                                                12345678901234567890123456
  32     //  1 = msb 1 bit
  33     //  P = bit FLT_MANT_DIG-1 bits to the right of 1
  34     //  Q = bit FLT_MANT_DIG bits to the right of 1
  35     //  R = "or" of all bits to the right of Q
  36     switch (sd) {
  37     case FLT_MANT_DIG + 1:
  38       a <<= 1;
  39       break;
  40     case FLT_MANT_DIG + 2:
  41       break;
  42     default:
  43       a = (a >> (sd - (FLT_MANT_DIG + 2))) |
  44           ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG + 2) - sd))) != 0);
  45     };
  46     // finish:
  47     a |= (a & 4) != 0; // Or P into R
  48     ++a;               // round - this step may add a significant bit
  49     a >>= 2;           // dump Q and R
  50     // a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits
  51     if (a & ((du_int)1 << FLT_MANT_DIG)) {
  52       a >>= 1;
  53       ++e;
  54     }
  55     // a is now rounded to FLT_MANT_DIG bits
  56   } else {
  57     a <<= (FLT_MANT_DIG - sd);
  58     // a is now rounded to FLT_MANT_DIG bits
  59   }
  60   float_bits fb;
  61   fb.u = ((e + 127) << 23) |       // exponent
  62          ((su_int)a & 0x007FFFFF); // mantissa
  63   return fb.f;
  64 }
  65
  66 #if defined(__ARM_EABI__)
  67 #if defined(COMPILER_RT_ARMHF_TARGET)
  68 AEABI_RTABI float __aeabi_ul2f(du_int a) { return __floatundisf(a); }
  69 #else
  70 COMPILER_RT_ALIAS(__floatundisf, __aeabi_ul2f)
  71 #endif
  72 #endif
  73
  74 #if defined(__MINGW32__) && defined(__arm__)
  75 COMPILER_RT_ALIAS(__floatundisf, __u64tos)
  76 #endif