1 /* ===-- floatundidf.c - Implement __floatundidf ---------------------------=== 2 * 3 * The LLVM Compiler Infrastructure 4 * 5 * This file is distributed under the University of Illinois Open Source 6 * License. See LICENSE.TXT for details. 7 * 8 * ===----------------------------------------------------------------------=== 9 * 10 * This file implements __floatundidf for the compiler_rt library. 11 * 12 * ===----------------------------------------------------------------------=== 13 */ 14 15 #include "int_lib.h" 16 #include <float.h> 17 18 /* Returns: convert a to a double, rounding toward even. */ 19 20 /* Assumption: double is a IEEE 64 bit floating point type 21 * du_int is a 64 bit integral type 22 */ 23 24 /* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */ 25 26 #ifndef __SOFT_FP__ 27 /* Support for systems that have hardware floating-point; we'll set the inexact flag 28 * as a side-effect of this computation. 29 */ 30 31 #include <stdint.h> 32 33 double __floatundidf(du_int a)34__floatundidf(du_int a) 35 { 36 static const double twop52 = 0x1.0p52; 37 static const double twop84 = 0x1.0p84; 38 static const double twop84_plus_twop52 = 0x1.00000001p84; 39 40 union { uint64_t x; double d; } high = { .d = twop84 }; 41 union { uint64_t x; double d; } low = { .d = twop52 }; 42 43 high.x |= a >> 32; 44 low.x |= a & UINT64_C(0x00000000ffffffff); 45 46 const double result = (high.d - twop84_plus_twop52) + low.d; 47 return result; 48 } 49 50 #else 51 /* Support for systems that don't have hardware floating-point; there are no flags to 52 * set, and we don't want to code-gen to an unknown soft-float implementation. 53 */ 54 55 double __floatundidf(du_int a)56__floatundidf(du_int a) 57 { 58 if (a == 0) 59 return 0.0; 60 const unsigned N = sizeof(du_int) * CHAR_BIT; 61 int sd = N - __builtin_clzll(a); /* number of significant digits */ 62 int e = sd - 1; /* exponent */ 63 if (sd > DBL_MANT_DIG) 64 { 65 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 66 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 67 * 12345678901234567890123456 68 * 1 = msb 1 bit 69 * P = bit DBL_MANT_DIG-1 bits to the right of 1 70 * Q = bit DBL_MANT_DIG bits to the right of 1 71 * R = "or" of all bits to the right of Q 72 */ 73 switch (sd) 74 { 75 case DBL_MANT_DIG + 1: 76 a <<= 1; 77 break; 78 case DBL_MANT_DIG + 2: 79 break; 80 default: 81 a = (a >> (sd - (DBL_MANT_DIG+2))) | 82 ((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0); 83 }; 84 /* finish: */ 85 a |= (a & 4) != 0; /* Or P into R */ 86 ++a; /* round - this step may add a significant bit */ 87 a >>= 2; /* dump Q and R */ 88 /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */ 89 if (a & ((du_int)1 << DBL_MANT_DIG)) 90 { 91 a >>= 1; 92 ++e; 93 } 94 /* a is now rounded to DBL_MANT_DIG bits */ 95 } 96 else 97 { 98 a <<= (DBL_MANT_DIG - sd); 99 /* a is now rounded to DBL_MANT_DIG bits */ 100 } 101 double_bits fb; 102 fb.u.high = ((e + 1023) << 20) | /* exponent */ 103 ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */ 104 fb.u.low = (su_int)a; /* mantissa-low */ 105 return fb.f; 106 } 107 #endif 108