1 //===-- floatuntisf.c - Implement __floatuntisf ---------------------------===// 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 __floatuntisf 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 float, rounding toward even. 18 19 // Assumption: float is a IEEE 32 bit floating point type 20 // tu_int is a 128 bit integral type 21 22 // seee eeee emmm mmmm mmmm mmmm mmmm mmmm 23 24 COMPILER_RT_ABI float __floatuntisf(tu_int a) { 25 if (a == 0) 26 return 0.0F; 27 const unsigned N = sizeof(tu_int) * CHAR_BIT; 28 int sd = N - __clzti2(a); // number of significant digits 29 int e = sd - 1; // exponent 30 if (sd > FLT_MANT_DIG) { 31 // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 32 // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 33 // 12345678901234567890123456 34 // 1 = msb 1 bit 35 // P = bit FLT_MANT_DIG-1 bits to the right of 1 36 // Q = bit FLT_MANT_DIG bits to the right of 1 37 // R = "or" of all bits to the right of Q 38 switch (sd) { 39 case FLT_MANT_DIG + 1: 40 a <<= 1; 41 break; 42 case FLT_MANT_DIG + 2: 43 break; 44 default: 45 a = (a >> (sd - (FLT_MANT_DIG + 2))) | 46 ((a & ((tu_int)(-1) >> ((N + FLT_MANT_DIG + 2) - sd))) != 0); 47 }; 48 // finish: 49 a |= (a & 4) != 0; // Or P into R 50 ++a; // round - this step may add a significant bit 51 a >>= 2; // dump Q and R 52 // a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits 53 if (a & ((tu_int)1 << FLT_MANT_DIG)) { 54 a >>= 1; 55 ++e; 56 } 57 // a is now rounded to FLT_MANT_DIG bits 58 } else { 59 a <<= (FLT_MANT_DIG - sd); 60 // a is now rounded to FLT_MANT_DIG bits 61 } 62 float_bits fb; 63 fb.u = ((e + 127) << 23) | // exponent 64 ((su_int)a & 0x007FFFFF); // mantissa 65 return fb.f; 66 } 67 68 #endif // CRT_HAS_128BIT 69