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 ARM_EABI_FNALIAS(ul2d, floatundidf) 26 27 #ifndef __SOFT_FP__ 28 /* Support for systems that have hardware floating-point; we'll set the inexact flag 29 * as a side-effect of this computation. 30 */ 31 32 COMPILER_RT_ABI double 33 __floatundidf(du_int a) 34 { 35 static const double twop52 = 4503599627370496.0; // 0x1.0p52 36 static const double twop84 = 19342813113834066795298816.0; // 0x1.0p84 37 static const double twop84_plus_twop52 = 19342813118337666422669312.0; // 0x1.00000001p84 38 39 union { uint64_t x; double d; } high = { .d = twop84 }; 40 union { uint64_t x; double d; } low = { .d = twop52 }; 41 42 high.x |= a >> 32; 43 low.x |= a & UINT64_C(0x00000000ffffffff); 44 45 const double result = (high.d - twop84_plus_twop52) + low.d; 46 return result; 47 } 48 49 #else 50 /* Support for systems that don't have hardware floating-point; there are no flags to 51 * set, and we don't want to code-gen to an unknown soft-float implementation. 52 */ 53 54 COMPILER_RT_ABI double 55 __floatundidf(du_int a) 56 { 57 if (a == 0) 58 return 0.0; 59 const unsigned N = sizeof(du_int) * CHAR_BIT; 60 int sd = N - __builtin_clzll(a); /* number of significant digits */ 61 int e = sd - 1; /* exponent */ 62 if (sd > DBL_MANT_DIG) 63 { 64 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 65 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 66 * 12345678901234567890123456 67 * 1 = msb 1 bit 68 * P = bit DBL_MANT_DIG-1 bits to the right of 1 69 * Q = bit DBL_MANT_DIG bits to the right of 1 70 * R = "or" of all bits to the right of Q 71 */ 72 switch (sd) 73 { 74 case DBL_MANT_DIG + 1: 75 a <<= 1; 76 break; 77 case DBL_MANT_DIG + 2: 78 break; 79 default: 80 a = (a >> (sd - (DBL_MANT_DIG+2))) | 81 ((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0); 82 }; 83 /* finish: */ 84 a |= (a & 4) != 0; /* Or P into R */ 85 ++a; /* round - this step may add a significant bit */ 86 a >>= 2; /* dump Q and R */ 87 /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */ 88 if (a & ((du_int)1 << DBL_MANT_DIG)) 89 { 90 a >>= 1; 91 ++e; 92 } 93 /* a is now rounded to DBL_MANT_DIG bits */ 94 } 95 else 96 { 97 a <<= (DBL_MANT_DIG - sd); 98 /* a is now rounded to DBL_MANT_DIG bits */ 99 } 100 double_bits fb; 101 fb.u.s.high = ((e + 1023) << 20) | /* exponent */ 102 ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */ 103 fb.u.s.low = (su_int)a; /* mantissa-low */ 104 return fb.f; 105 } 106 #endif 107
