1 //===-- lib/floatuntitf.c - uint128 -> 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 tu_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 tu_int to a fp_t, rounding toward even. 20 21 // Assumption: fp_t is a IEEE 128 bit floating point type 22 // tu_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 __floatuntitf(tu_int a) { 30 if (a == 0) 31 return 0.0; 32 const unsigned N = sizeof(tu_int) * CHAR_BIT; 33 int sd = N - __clzti2(a); // number of significant digits 34 int e = sd - 1; // exponent 35 if (sd > LDBL_MANT_DIG) { 36 // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 37 // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 38 // 12345678901234567890123456 39 // 1 = msb 1 bit 40 // P = bit LDBL_MANT_DIG-1 bits to the right of 1 41 // Q = bit LDBL_MANT_DIG bits to the right of 1 42 // R = "or" of all bits to the right of Q 43 switch (sd) { 44 case LDBL_MANT_DIG + 1: 45 a <<= 1; 46 break; 47 case LDBL_MANT_DIG + 2: 48 break; 49 default: 50 a = (a >> (sd - (LDBL_MANT_DIG + 2))) | 51 ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG + 2) - sd))) != 0); 52 }; 53 // finish: 54 a |= (a & 4) != 0; // Or P into R 55 ++a; // round - this step may add a significant bit 56 a >>= 2; // dump Q and R 57 // a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits 58 if (a & ((tu_int)1 << LDBL_MANT_DIG)) { 59 a >>= 1; 60 ++e; 61 } 62 // a is now rounded to LDBL_MANT_DIG bits 63 } else { 64 a <<= (LDBL_MANT_DIG - sd); 65 // a is now rounded to LDBL_MANT_DIG bits 66 } 67 68 long_double_bits fb; 69 fb.u.high.all = (du_int)(e + 16383) << 48 // exponent 70 | ((a >> 64) & 0x0000ffffffffffffLL); // significand 71 fb.u.low.all = (du_int)(a); 72 return fb.f; 73 } 74 75 #endif 76