1 //===-- lib/floattitf.c - int128 -> quad-precision conversion -----*- C -*-===// 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 ti_int to quad-precision conversion for the 10 // compiler-rt library in the IEEE-754 default round-to-nearest, ties-to-even 11 // mode. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #define QUAD_PRECISION 16 #include "fp_lib.h" 17 #include "int_lib.h" 18 19 // Returns: convert a ti_int to a fp_t, rounding toward even. 20 21 // Assumption: fp_t is a IEEE 128 bit floating point type 22 // ti_int is a 128 bit integral type 23 24 // seee eeee eeee eeee mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm 25 // mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm 26 // mmmm mmmm mmmm 27 28 #if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT) 29 COMPILER_RT_ABI fp_t __floattitf(ti_int a) { 30 if (a == 0) 31 return 0.0; 32 const unsigned N = sizeof(ti_int) * CHAR_BIT; 33 const ti_int s = a >> (N - 1); 34 a = (a ^ s) - s; 35 int sd = N - __clzti2(a); // number of significant digits 36 int e = sd - 1; // exponent 37 if (sd > LDBL_MANT_DIG) { 38 // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 39 // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 40 // 12345678901234567890123456 41 // 1 = msb 1 bit 42 // P = bit LDBL_MANT_DIG-1 bits to the right of 1 43 // Q = bit LDBL_MANT_DIG bits to the right of 1 44 // R = "or" of all bits to the right of Q 45 switch (sd) { 46 case LDBL_MANT_DIG + 1: 47 a <<= 1; 48 break; 49 case LDBL_MANT_DIG + 2: 50 break; 51 default: 52 a = ((tu_int)a >> (sd - (LDBL_MANT_DIG + 2))) | 53 ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG + 2) - sd))) != 0); 54 }; 55 // finish: 56 a |= (a & 4) != 0; // Or P into R 57 ++a; // round - this step may add a significant bit 58 a >>= 2; // dump Q and R 59 // a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits 60 if (a & ((tu_int)1 << LDBL_MANT_DIG)) { 61 a >>= 1; 62 ++e; 63 } 64 // a is now rounded to LDBL_MANT_DIG bits 65 } else { 66 a <<= (LDBL_MANT_DIG - sd); 67 // a is now rounded to LDBL_MANT_DIG bits 68 } 69 70 long_double_bits fb; 71 fb.u.high.all = (s & 0x8000000000000000LL) // sign 72 | (du_int)(e + 16383) << 48 // exponent 73 | ((a >> 64) & 0x0000ffffffffffffLL); // significand 74 fb.u.low.all = (du_int)(a); 75 return fb.f; 76 } 77 78 #endif 79