1 /* ===-- floatuntixf.c - Implement __floatuntixf ---------------------------=== 2 * 3 * The LLVM Compiler Infrastructure 4 * 5 * This file is dual licensed under the MIT and the University of Illinois Open 6 * Source Licenses. See LICENSE.TXT for details. 7 * 8 * ===----------------------------------------------------------------------=== 9 * 10 * This file implements __floatuntixf for the compiler_rt library. 11 * 12 * ===----------------------------------------------------------------------=== 13 */ 14 15 #include "int_lib.h" 16 17 #ifdef CRT_HAS_128BIT 18 19 /* Returns: convert a to a long double, rounding toward even. */ 20 21 /* Assumption: long double is a IEEE 80 bit floating point type padded to 128 bits 22 * tu_int is a 128 bit integral type 23 */ 24 25 /* gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee eeee | 26 * 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm 27 */ 28 29 COMPILER_RT_ABI long double 30 __floatuntixf(tu_int a) 31 { 32 if (a == 0) 33 return 0.0; 34 const unsigned N = sizeof(tu_int) * CHAR_BIT; 35 int sd = N - __clzti2(a); /* number of significant digits */ 36 int e = sd - 1; /* exponent */ 37 if (sd > LDBL_MANT_DIG) 38 { 39 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 40 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 41 * 12345678901234567890123456 42 * 1 = msb 1 bit 43 * P = bit LDBL_MANT_DIG-1 bits to the right of 1 44 * Q = bit LDBL_MANT_DIG bits to the right of 1 45 * R = "or" of all bits to the right of Q 46 */ 47 switch (sd) 48 { 49 case LDBL_MANT_DIG + 1: 50 a <<= 1; 51 break; 52 case LDBL_MANT_DIG + 2: 53 break; 54 default: 55 a = (a >> (sd - (LDBL_MANT_DIG+2))) | 56 ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG+2) - sd))) != 0); 57 }; 58 /* finish: */ 59 a |= (a & 4) != 0; /* Or P into R */ 60 ++a; /* round - this step may add a significant bit */ 61 a >>= 2; /* dump Q and R */ 62 /* a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits */ 63 if (a & ((tu_int)1 << LDBL_MANT_DIG)) 64 { 65 a >>= 1; 66 ++e; 67 } 68 /* a is now rounded to LDBL_MANT_DIG bits */ 69 } 70 else 71 { 72 a <<= (LDBL_MANT_DIG - sd); 73 /* a is now rounded to LDBL_MANT_DIG bits */ 74 } 75 long_double_bits fb; 76 fb.u.high.s.low = (e + 16383); /* exponent */ 77 fb.u.low.all = (du_int)a; /* mantissa */ 78 return fb.f; 79 } 80 81 #endif 82
