1 /* ===-- floatuntidf.c - Implement __floatuntidf ---------------------------=== 2 * 3 * The LLVM Compiler Infrastructure 4 * 5 * This file is distributed under the University of Illinois Open Source 6 * License. See LICENSE.TXT for details. 7 * 8 * ===----------------------------------------------------------------------=== 9 * 10 * This file implements __floatuntidf for the compiler_rt library. 11 * 12 * ===----------------------------------------------------------------------=== 13 */ 14 15 #if __x86_64 16 17 #include "int_lib.h" 18 #include <float.h> 19 20 /* Returns: convert a to a double, rounding toward even. */ 21 22 /* Assumption: double is a IEEE 64 bit floating point type 23 * tu_int is a 128 bit integral type 24 */ 25 26 /* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */ 27 28 si_int __clzti2(ti_int a); 29 30 double 31 __floatuntidf(tu_int a) 32 { 33 if (a == 0) 34 return 0.0; 35 const unsigned N = sizeof(tu_int) * CHAR_BIT; 36 int sd = N - __clzti2(a); /* number of significant digits */ 37 int e = sd - 1; /* exponent */ 38 if (sd > DBL_MANT_DIG) 39 { 40 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 41 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 42 * 12345678901234567890123456 43 * 1 = msb 1 bit 44 * P = bit DBL_MANT_DIG-1 bits to the right of 1 45 * Q = bit DBL_MANT_DIG bits to the right of 1 46 * R = "or" of all bits to the right of Q 47 */ 48 switch (sd) 49 { 50 case DBL_MANT_DIG + 1: 51 a <<= 1; 52 break; 53 case DBL_MANT_DIG + 2: 54 break; 55 default: 56 a = (a >> (sd - (DBL_MANT_DIG+2))) | 57 ((a & ((tu_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0); 58 }; 59 /* finish: */ 60 a |= (a & 4) != 0; /* Or P into R */ 61 ++a; /* round - this step may add a significant bit */ 62 a >>= 2; /* dump Q and R */ 63 /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */ 64 if (a & ((tu_int)1 << DBL_MANT_DIG)) 65 { 66 a >>= 1; 67 ++e; 68 } 69 /* a is now rounded to DBL_MANT_DIG bits */ 70 } 71 else 72 { 73 a <<= (DBL_MANT_DIG - sd); 74 /* a is now rounded to DBL_MANT_DIG bits */ 75 } 76 double_bits fb; 77 fb.u.s.high = ((e + 1023) << 20) | /* exponent */ 78 ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */ 79 fb.u.s.low = (su_int)a; /* mantissa-low */ 80 return fb.f; 81 } 82 83 #endif 84
