1 //===-- floatuntixf.c - Implement __floatuntixf ---------------------------===// 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 __floatuntixf 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 long double, rounding toward even. 18 19 // Assumption: long double is a IEEE 80 bit floating point type padded to 128 20 // bits tu_int is a 128 bit integral type 21 22 // gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee 23 // eeee | 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm 24 // mmmm mmmm mmmm 25 26 COMPILER_RT_ABI long double __floatuntixf(tu_int a) { 27 if (a == 0) 28 return 0.0; 29 const unsigned N = sizeof(tu_int) * CHAR_BIT; 30 int sd = N - __clzti2(a); // number of significant digits 31 int e = sd - 1; // exponent 32 if (sd > LDBL_MANT_DIG) { 33 // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 34 // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 35 // 12345678901234567890123456 36 // 1 = msb 1 bit 37 // P = bit LDBL_MANT_DIG-1 bits to the right of 1 38 // Q = bit LDBL_MANT_DIG bits to the right of 1 39 // R = "or" of all bits to the right of Q 40 switch (sd) { 41 case LDBL_MANT_DIG + 1: 42 a <<= 1; 43 break; 44 case LDBL_MANT_DIG + 2: 45 break; 46 default: 47 a = (a >> (sd - (LDBL_MANT_DIG + 2))) | 48 ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG + 2) - sd))) != 0); 49 }; 50 // finish: 51 a |= (a & 4) != 0; // Or P into R 52 ++a; // round - this step may add a significant bit 53 a >>= 2; // dump Q and R 54 // a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits 55 if (a & ((tu_int)1 << LDBL_MANT_DIG)) { 56 a >>= 1; 57 ++e; 58 } 59 // a is now rounded to LDBL_MANT_DIG bits 60 } else { 61 a <<= (LDBL_MANT_DIG - sd); 62 // a is now rounded to LDBL_MANT_DIG bits 63 } 64 long_double_bits fb; 65 fb.u.high.s.low = (e + 16383); // exponent 66 fb.u.low.all = (du_int)a; // mantissa 67 return fb.f; 68 } 69 70 #endif 71