floatundidf.c revision 222656
1214152Sed/* ===-- floatundidf.c - Implement __floatundidf ---------------------------=== 2214152Sed * 3214152Sed * The LLVM Compiler Infrastructure 4214152Sed * 5222656Sed * This file is dual licensed under the MIT and the University of Illinois Open 6222656Sed * Source Licenses. See LICENSE.TXT for details. 7214152Sed * 8214152Sed * ===----------------------------------------------------------------------=== 9214152Sed * 10214152Sed * This file implements __floatundidf for the compiler_rt library. 11214152Sed * 12214152Sed * ===----------------------------------------------------------------------=== 13214152Sed */ 14214152Sed 15222656Sed#include "abi.h" 16214152Sed#include <float.h> 17214152Sed 18214152Sed/* Returns: convert a to a double, rounding toward even. */ 19214152Sed 20214152Sed/* Assumption: double is a IEEE 64 bit floating point type 21214152Sed * du_int is a 64 bit integral type 22214152Sed */ 23214152Sed 24214152Sed/* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */ 25214152Sed 26222656Sed#include "int_lib.h" 27222656Sed 28222656SedARM_EABI_FNALIAS(ul2d, floatundidf); 29222656Sed 30214152Sed#ifndef __SOFT_FP__ 31214152Sed/* Support for systems that have hardware floating-point; we'll set the inexact flag 32214152Sed * as a side-effect of this computation. 33214152Sed */ 34214152Sed 35214152Sed#include <stdint.h> 36214152Sed 37222656SedCOMPILER_RT_ABI double 38214152Sed__floatundidf(du_int a) 39214152Sed{ 40214152Sed static const double twop52 = 0x1.0p52; 41214152Sed static const double twop84 = 0x1.0p84; 42214152Sed static const double twop84_plus_twop52 = 0x1.00000001p84; 43214152Sed 44214152Sed union { uint64_t x; double d; } high = { .d = twop84 }; 45214152Sed union { uint64_t x; double d; } low = { .d = twop52 }; 46214152Sed 47214152Sed high.x |= a >> 32; 48214152Sed low.x |= a & UINT64_C(0x00000000ffffffff); 49214152Sed 50214152Sed const double result = (high.d - twop84_plus_twop52) + low.d; 51214152Sed return result; 52214152Sed} 53214152Sed 54214152Sed#else 55214152Sed/* Support for systems that don't have hardware floating-point; there are no flags to 56214152Sed * set, and we don't want to code-gen to an unknown soft-float implementation. 57214152Sed */ 58214152Sed 59222656SedCOMPILER_RT_ABI double 60214152Sed__floatundidf(du_int a) 61214152Sed{ 62214152Sed if (a == 0) 63214152Sed return 0.0; 64214152Sed const unsigned N = sizeof(du_int) * CHAR_BIT; 65214152Sed int sd = N - __builtin_clzll(a); /* number of significant digits */ 66214152Sed int e = sd - 1; /* exponent */ 67214152Sed if (sd > DBL_MANT_DIG) 68214152Sed { 69214152Sed /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 70214152Sed * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 71214152Sed * 12345678901234567890123456 72214152Sed * 1 = msb 1 bit 73214152Sed * P = bit DBL_MANT_DIG-1 bits to the right of 1 74214152Sed * Q = bit DBL_MANT_DIG bits to the right of 1 75214152Sed * R = "or" of all bits to the right of Q 76214152Sed */ 77214152Sed switch (sd) 78214152Sed { 79214152Sed case DBL_MANT_DIG + 1: 80214152Sed a <<= 1; 81214152Sed break; 82214152Sed case DBL_MANT_DIG + 2: 83214152Sed break; 84214152Sed default: 85214152Sed a = (a >> (sd - (DBL_MANT_DIG+2))) | 86214152Sed ((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0); 87214152Sed }; 88214152Sed /* finish: */ 89214152Sed a |= (a & 4) != 0; /* Or P into R */ 90214152Sed ++a; /* round - this step may add a significant bit */ 91214152Sed a >>= 2; /* dump Q and R */ 92214152Sed /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */ 93214152Sed if (a & ((du_int)1 << DBL_MANT_DIG)) 94214152Sed { 95214152Sed a >>= 1; 96214152Sed ++e; 97214152Sed } 98214152Sed /* a is now rounded to DBL_MANT_DIG bits */ 99214152Sed } 100214152Sed else 101214152Sed { 102214152Sed a <<= (DBL_MANT_DIG - sd); 103214152Sed /* a is now rounded to DBL_MANT_DIG bits */ 104214152Sed } 105214152Sed double_bits fb; 106214152Sed fb.u.high = ((e + 1023) << 20) | /* exponent */ 107214152Sed ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */ 108214152Sed fb.u.low = (su_int)a; /* mantissa-low */ 109214152Sed return fb.f; 110214152Sed} 111214152Sed#endif 112