1 //===-- floattixf.c - Implement __floattixf -------------------------------===// 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 __floattixf 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 ti_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 __floattixf(ti_int a) { 27 if (a == 0) 28 return 0.0; 29 const unsigned N = sizeof(ti_int) * CHAR_BIT; 30 const ti_int s = a >> (N - 1); 31 a = (a ^ s) - s; 32 int sd = N - __clzti2(a); // number of significant digits 33 int e = sd - 1; // exponent 34 if (sd > LDBL_MANT_DIG) { 35 // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 36 // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 37 // 12345678901234567890123456 38 // 1 = msb 1 bit 39 // P = bit LDBL_MANT_DIG-1 bits to the right of 1 40 // Q = bit LDBL_MANT_DIG bits to the right of 1 41 // R = "or" of all bits to the right of Q 42 switch (sd) { 43 case LDBL_MANT_DIG + 1: 44 a <<= 1; 45 break; 46 case LDBL_MANT_DIG + 2: 47 break; 48 default: 49 a = ((tu_int)a >> (sd - (LDBL_MANT_DIG + 2))) | 50 ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG + 2) - sd))) != 0); 51 }; 52 // finish: 53 a |= (a & 4) != 0; // Or P into R 54 ++a; // round - this step may add a significant bit 55 a >>= 2; // dump Q and R 56 // a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits 57 if (a & ((tu_int)1 << LDBL_MANT_DIG)) { 58 a >>= 1; 59 ++e; 60 } 61 // a is now rounded to LDBL_MANT_DIG bits 62 } else { 63 a <<= (LDBL_MANT_DIG - sd); 64 // a is now rounded to LDBL_MANT_DIG bits 65 } 66 long_double_bits fb; 67 fb.u.high.s.low = ((su_int)s & 0x8000) | // sign 68 (e + 16383); // exponent 69 fb.u.low.all = (du_int)a; // mantissa 70 return fb.f; 71 } 72 73 #endif // CRT_HAS_128BIT 74