1 //===-- floattidf.c - Implement __floattidf -------------------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file implements __floattidf for the compiler_rt library. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "int_lib.h" 14 15 #ifdef CRT_HAS_128BIT 16 17 // Returns: convert a to a double, rounding toward even. 18 19 // Assumption: double is a IEEE 64 bit floating point type 20 // ti_int is a 128 bit integral type 21 22 // seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm 23 // mmmm 24 25 COMPILER_RT_ABI double __floattidf(ti_int a) { 26 if (a == 0) 27 return 0.0; 28 const unsigned N = sizeof(ti_int) * CHAR_BIT; 29 const ti_int s = a >> (N - 1); 30 a = (a ^ s) - s; 31 int sd = N - __clzti2(a); // number of significant digits 32 si_int e = sd - 1; // exponent 33 if (sd > DBL_MANT_DIG) { 34 // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 35 // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 36 // 12345678901234567890123456 37 // 1 = msb 1 bit 38 // P = bit DBL_MANT_DIG-1 bits to the right of 1 39 // Q = bit DBL_MANT_DIG bits to the right of 1 40 // R = "or" of all bits to the right of Q 41 switch (sd) { 42 case DBL_MANT_DIG + 1: 43 a <<= 1; 44 break; 45 case DBL_MANT_DIG + 2: 46 break; 47 default: 48 a = ((tu_int)a >> (sd - (DBL_MANT_DIG + 2))) | 49 ((a & ((tu_int)(-1) >> ((N + DBL_MANT_DIG + 2) - sd))) != 0); 50 }; 51 // finish: 52 a |= (a & 4) != 0; // Or P into R 53 ++a; // round - this step may add a significant bit 54 a >>= 2; // dump Q and R 55 // a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits 56 if (a & ((tu_int)1 << DBL_MANT_DIG)) { 57 a >>= 1; 58 ++e; 59 } 60 // a is now rounded to DBL_MANT_DIG bits 61 } else { 62 a <<= (DBL_MANT_DIG - sd); 63 // a is now rounded to DBL_MANT_DIG bits 64 } 65 double_bits fb; 66 fb.u.s.high = ((su_int)s & 0x80000000) | // sign 67 ((e + 1023) << 20) | // exponent 68 ((su_int)(a >> 32) & 0x000FFFFF); // mantissa-high 69 fb.u.s.low = (su_int)a; // mantissa-low 70 return fb.f; 71 } 72 73 #endif // CRT_HAS_128BIT 74