floatdidf.c revision b3a6901e66f55b35aa9e01bcb24134e6a65ea004
1b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar//===-- floatdidf.c - Implement __floatdidf -------------------------------===// 2b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// 3b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// The LLVM Compiler Infrastructure 4b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// 5b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// This file is distributed under the University of Illinois Open Source 6b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// License. See LICENSE.TXT for details. 7b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// 8b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar//===----------------------------------------------------------------------===// 9b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// 10b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// This file implements __floatdidf for the compiler_rt library. 11b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// 12b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar//===----------------------------------------------------------------------===// 13b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar 14b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar#include "int_lib.h" 15b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar#include <float.h> 16b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar 17b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// Returns: convert a to a double, rounding toward even. 18b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar 19b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// Assumption: double is a IEEE 64 bit floating point type 20b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// di_int is a 64 bit integral type 21b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar 22b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm 23b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar 24b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar#ifndef __SOFT_FP__ 25b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// Support for systems that have hardware floating-point; we'll set the inexact flag 26b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// as a side-effect of this computation. 27b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar#include <stdint.h> 28b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar 29b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbardouble 30b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar__floatdidf(di_int a) 31b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar{ 32b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar static const double twop52 = 0x1.0p52; 33b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar static const double twop32 = 0x1.0p32; 34b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar 35b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar union { int64_t x; double d; } low = { .d = twop52 }; 36b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar 37b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar const double high = (int32_t)(a >> 32) * twop32; 38b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar low.x |= a & INT64_C(0x00000000ffffffff); 39b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar 40b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar const double result = (high - twop52) + low.d; 41b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar return result; 42b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar} 43b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar 44b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar#else 45b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// Support for systems that don't have hardware floating-point; there are no flags to 46b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar// set, and we don't want to code-gen to an unknown soft-float implementation. 47b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar 48b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbardouble 49b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar__floatdidf(di_int a) 50b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar{ 51b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar if (a == 0) 52b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar return 0.0; 53b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar const unsigned N = sizeof(di_int) * CHAR_BIT; 54b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar const di_int s = a >> (N-1); 55b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar a = (a ^ s) - s; 56b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar int sd = N - __builtin_clzll(a); // number of significant digits 57b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar int e = sd - 1; // exponent 58b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar if (sd > DBL_MANT_DIG) 59b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar { 60b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 61b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 62b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar // 12345678901234567890123456 63b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar // 1 = msb 1 bit 64b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar // P = bit DBL_MANT_DIG-1 bits to the right of 1 65b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar // Q = bit DBL_MANT_DIG bits to the right of 1 66b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar // R = "or" of all bits to the right of Q 67b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar switch (sd) 68b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar { 69b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar case DBL_MANT_DIG + 1: 70b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar a <<= 1; 71b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar break; 72b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar case DBL_MANT_DIG + 2: 73b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar break; 74b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar default: 75b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar a = ((du_int)a >> (sd - (DBL_MANT_DIG+2))) | 76b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar ((a & ((du_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0); 77b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar }; 78b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar // finish: 79b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar a |= (a & 4) != 0; // Or P into R 80b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar ++a; // round - this step may add a significant bit 81b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar a >>= 2; // dump Q and R 82b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar // a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits 83b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar if (a & ((du_int)1 << DBL_MANT_DIG)) 84b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar { 85b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar a >>= 1; 86b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar ++e; 87b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar } 88b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar // a is now rounded to DBL_MANT_DIG bits 89b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar } 90b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar else 91b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar { 92b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar a <<= (DBL_MANT_DIG - sd); 93b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar // a is now rounded to DBL_MANT_DIG bits 94b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar } 95b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar double_bits fb; 96b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar fb.u.high = ((su_int)s & 0x80000000) | // sign 97b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar ((e + 1023) << 20) | // exponent 98b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar ((su_int)(a >> 32) & 0x000FFFFF); // mantissa-high 99b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar fb.u.low = (su_int)a; // mantissa-low 100b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar return fb.f; 101b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar} 102b3a6901e66f55b35aa9e01bcb24134e6a65ea004Daniel Dunbar#endif 103