1*3cab2bb3Spatrick //===-- floatuntidf.c - Implement __floatuntidf ---------------------------===// 2*3cab2bb3Spatrick // 3*3cab2bb3Spatrick // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4*3cab2bb3Spatrick // See https://llvm.org/LICENSE.txt for license information. 5*3cab2bb3Spatrick // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6*3cab2bb3Spatrick // 7*3cab2bb3Spatrick //===----------------------------------------------------------------------===// 8*3cab2bb3Spatrick // 9*3cab2bb3Spatrick // This file implements __floatuntidf for the compiler_rt library. 10*3cab2bb3Spatrick // 11*3cab2bb3Spatrick //===----------------------------------------------------------------------===// 12*3cab2bb3Spatrick 13*3cab2bb3Spatrick #include "int_lib.h" 14*3cab2bb3Spatrick 15*3cab2bb3Spatrick #ifdef CRT_HAS_128BIT 16*3cab2bb3Spatrick 17*3cab2bb3Spatrick // Returns: convert a to a double, rounding toward even. 18*3cab2bb3Spatrick 19*3cab2bb3Spatrick // Assumption: double is a IEEE 64 bit floating point type 20*3cab2bb3Spatrick // tu_int is a 128 bit integral type 21*3cab2bb3Spatrick 22*3cab2bb3Spatrick // seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm 23*3cab2bb3Spatrick // mmmm 24*3cab2bb3Spatrick __floatuntidf(tu_int a)25*3cab2bb3SpatrickCOMPILER_RT_ABI double __floatuntidf(tu_int a) { 26*3cab2bb3Spatrick if (a == 0) 27*3cab2bb3Spatrick return 0.0; 28*3cab2bb3Spatrick const unsigned N = sizeof(tu_int) * CHAR_BIT; 29*3cab2bb3Spatrick int sd = N - __clzti2(a); // number of significant digits 30*3cab2bb3Spatrick int e = sd - 1; // exponent 31*3cab2bb3Spatrick if (sd > DBL_MANT_DIG) { 32*3cab2bb3Spatrick // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 33*3cab2bb3Spatrick // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 34*3cab2bb3Spatrick // 12345678901234567890123456 35*3cab2bb3Spatrick // 1 = msb 1 bit 36*3cab2bb3Spatrick // P = bit DBL_MANT_DIG-1 bits to the right of 1 37*3cab2bb3Spatrick // Q = bit DBL_MANT_DIG bits to the right of 1 38*3cab2bb3Spatrick // R = "or" of all bits to the right of Q 39*3cab2bb3Spatrick switch (sd) { 40*3cab2bb3Spatrick case DBL_MANT_DIG + 1: 41*3cab2bb3Spatrick a <<= 1; 42*3cab2bb3Spatrick break; 43*3cab2bb3Spatrick case DBL_MANT_DIG + 2: 44*3cab2bb3Spatrick break; 45*3cab2bb3Spatrick default: 46*3cab2bb3Spatrick a = (a >> (sd - (DBL_MANT_DIG + 2))) | 47*3cab2bb3Spatrick ((a & ((tu_int)(-1) >> ((N + DBL_MANT_DIG + 2) - sd))) != 0); 48*3cab2bb3Spatrick }; 49*3cab2bb3Spatrick // finish: 50*3cab2bb3Spatrick a |= (a & 4) != 0; // Or P into R 51*3cab2bb3Spatrick ++a; // round - this step may add a significant bit 52*3cab2bb3Spatrick a >>= 2; // dump Q and R 53*3cab2bb3Spatrick // a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits 54*3cab2bb3Spatrick if (a & ((tu_int)1 << DBL_MANT_DIG)) { 55*3cab2bb3Spatrick a >>= 1; 56*3cab2bb3Spatrick ++e; 57*3cab2bb3Spatrick } 58*3cab2bb3Spatrick // a is now rounded to DBL_MANT_DIG bits 59*3cab2bb3Spatrick } else { 60*3cab2bb3Spatrick a <<= (DBL_MANT_DIG - sd); 61*3cab2bb3Spatrick // a is now rounded to DBL_MANT_DIG bits 62*3cab2bb3Spatrick } 63*3cab2bb3Spatrick double_bits fb; 64*3cab2bb3Spatrick fb.u.s.high = ((e + 1023) << 20) | // exponent 65*3cab2bb3Spatrick ((su_int)(a >> 32) & 0x000FFFFF); // mantissa-high 66*3cab2bb3Spatrick fb.u.s.low = (su_int)a; // mantissa-low 67*3cab2bb3Spatrick return fb.f; 68*3cab2bb3Spatrick } 69*3cab2bb3Spatrick 70*3cab2bb3Spatrick #endif // CRT_HAS_128BIT 71