1 //===-- floattisf.c - Implement __floattisf -------------------------------===// 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 __floattisf 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 // ti_int is a 128 bit integral type 21 22 // seee eeee emmm mmmm mmmm mmmm mmmm mmmm 23 24 COMPILER_RT_ABI float __floattisf(ti_int a) { 25 if (a == 0) 26 return 0.0F; 27 const unsigned N = sizeof(ti_int) * CHAR_BIT; 28 const ti_int s = a >> (N - 1); 29 a = (a ^ s) - s; 30 int sd = N - __clzti2(a); // number of significant digits 31 int e = sd - 1; // exponent 32 if (sd > FLT_MANT_DIG) { 33 // start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 34 // finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 35 // 12345678901234567890123456 36 // 1 = msb 1 bit 37 // P = bit FLT_MANT_DIG-1 bits to the right of 1 38 // Q = bit FLT_MANT_DIG bits to the right of 1 39 // R = "or" of all bits to the right of Q 40 switch (sd) { 41 case FLT_MANT_DIG + 1: 42 a <<= 1; 43 break; 44 case FLT_MANT_DIG + 2: 45 break; 46 default: 47 a = ((tu_int)a >> (sd - (FLT_MANT_DIG + 2))) | 48 ((a & ((tu_int)(-1) >> ((N + FLT_MANT_DIG + 2) - sd))) != 0); 49 }; 50 // finish: 51 a |= (a & 4) != 0; // Or P into R 52 ++a; // round - this step may add a significant bit 53 a >>= 2; // dump Q and R 54 // a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits 55 if (a & ((tu_int)1 << FLT_MANT_DIG)) { 56 a >>= 1; 57 ++e; 58 } 59 // a is now rounded to FLT_MANT_DIG bits 60 } else { 61 a <<= (FLT_MANT_DIG - sd); 62 // a is now rounded to FLT_MANT_DIG bits 63 } 64 float_bits fb; 65 fb.u = ((su_int)s & 0x80000000) | // sign 66 ((e + 127) << 23) | // exponent 67 ((su_int)a & 0x007FFFFF); // mantissa 68 return fb.f; 69 } 70 71 #endif // CRT_HAS_128BIT 72