floatundidf.c revision 1.4
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 30COMPILER_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 52COMPILER_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) 108AEABI_RTABI double __aeabi_ul2d(du_int a) { 109 return __floatundidf(a); 110} 111#else 112AEABI_RTABI double __aeabi_ul2d(du_int a) COMPILER_RT_ALIAS(__floatundidf); 113#endif 114#endif 115