1 /* ===-- floattidf.c - Implement __floattidf -------------------------------=== 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 __floattidf 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 * ti_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 __floattidf(ti_int a) 32 { 33 if (a == 0) 34 return 0.0; 35 const unsigned N = sizeof(ti_int) * CHAR_BIT; 36 const ti_int s = a >> (N-1); 37 a = (a ^ s) - s; 38 int sd = N - __clzti2(a); /* number of significant digits */ 39 int e = sd - 1; /* exponent */ 40 if (sd > DBL_MANT_DIG) 41 { 42 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 43 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 44 * 12345678901234567890123456 45 * 1 = msb 1 bit 46 * P = bit DBL_MANT_DIG-1 bits to the right of 1 47 * Q = bit DBL_MANT_DIG bits to the right of 1 48 * R = "or" of all bits to the right of Q 49 */ 50 switch (sd) 51 { 52 case DBL_MANT_DIG + 1: 53 a <<= 1; 54 break; 55 case DBL_MANT_DIG + 2: 56 break; 57 default: 58 a = ((tu_int)a >> (sd - (DBL_MANT_DIG+2))) | 59 ((a & ((tu_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0); 60 }; 61 /* finish: */ 62 a |= (a & 4) != 0; /* Or P into R */ 63 ++a; /* round - this step may add a significant bit */ 64 a >>= 2; /* dump Q and R */ 65 /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */ 66 if (a & ((tu_int)1 << DBL_MANT_DIG)) 67 { 68 a >>= 1; 69 ++e; 70 } 71 /* a is now rounded to DBL_MANT_DIG bits */ 72 } 73 else 74 { 75 a <<= (DBL_MANT_DIG - sd); 76 /* a is now rounded to DBL_MANT_DIG bits */ 77 } 78 double_bits fb; 79 fb.u.s.high = ((su_int)s & 0x80000000) | /* sign */ 80 ((e + 1023) << 20) | /* exponent */ 81 ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */ 82 fb.u.s.low = (su_int)a; /* mantissa-low */ 83 return fb.f; 84 } 85 86 #endif 87
