1 /* ===-- floatuntidf.c - Implement __floatuntidf ---------------------------=== 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 __floatuntidf 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 double, rounding toward even. */ 20 21 /* Assumption: double is a IEEE 64 bit floating point type 22 * tu_int is a 128 bit integral type 23 */ 24 25 /* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */ 26 27 COMPILER_RT_ABI double 28 __floatuntidf(tu_int a) 29 { 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 > DBL_MANT_DIG) 36 { 37 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 38 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 39 * 12345678901234567890123456 40 * 1 = msb 1 bit 41 * P = bit DBL_MANT_DIG-1 bits to the right of 1 42 * Q = bit DBL_MANT_DIG bits to the right of 1 43 * R = "or" of all bits to the right of Q 44 */ 45 switch (sd) 46 { 47 case DBL_MANT_DIG + 1: 48 a <<= 1; 49 break; 50 case DBL_MANT_DIG + 2: 51 break; 52 default: 53 a = (a >> (sd - (DBL_MANT_DIG+2))) | 54 ((a & ((tu_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0); 55 }; 56 /* finish: */ 57 a |= (a & 4) != 0; /* Or P into R */ 58 ++a; /* round - this step may add a significant bit */ 59 a >>= 2; /* dump Q and R */ 60 /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */ 61 if (a & ((tu_int)1 << DBL_MANT_DIG)) 62 { 63 a >>= 1; 64 ++e; 65 } 66 /* a is now rounded to DBL_MANT_DIG bits */ 67 } 68 else 69 { 70 a <<= (DBL_MANT_DIG - sd); 71 /* a is now rounded to DBL_MANT_DIG bits */ 72 } 73 double_bits fb; 74 fb.u.s.high = ((e + 1023) << 20) | /* exponent */ 75 ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */ 76 fb.u.s.low = (su_int)a; /* mantissa-low */ 77 return fb.f; 78 } 79 80 #endif /* CRT_HAS_128BIT */ 81
