1 /* ===-- floattixf.c - Implement __floattixf -------------------------------=== 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 __floattixf 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 long double, rounding toward even. */ 21 22 /* Assumption: long double is a IEEE 80 bit floating point type padded to 128 bits 23 * ti_int is a 128 bit integral type 24 */ 25 26 /* gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee eeee | 27 * 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm 28 */ 29 30 si_int __clzti2(ti_int a); 31 32 long double 33 __floattixf(ti_int a) 34 { 35 if (a == 0) 36 return 0.0; 37 const unsigned N = sizeof(ti_int) * CHAR_BIT; 38 const ti_int s = a >> (N-1); 39 a = (a ^ s) - s; 40 int sd = N - __clzti2(a); /* number of significant digits */ 41 int e = sd - 1; /* exponent */ 42 if (sd > LDBL_MANT_DIG) 43 { 44 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 45 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 46 * 12345678901234567890123456 47 * 1 = msb 1 bit 48 * P = bit LDBL_MANT_DIG-1 bits to the right of 1 49 * Q = bit LDBL_MANT_DIG bits to the right of 1 50 * R = "or" of all bits to the right of Q 51 */ 52 switch (sd) 53 { 54 case LDBL_MANT_DIG + 1: 55 a <<= 1; 56 break; 57 case LDBL_MANT_DIG + 2: 58 break; 59 default: 60 a = ((tu_int)a >> (sd - (LDBL_MANT_DIG+2))) | 61 ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG+2) - sd))) != 0); 62 }; 63 /* finish: */ 64 a |= (a & 4) != 0; /* Or P into R */ 65 ++a; /* round - this step may add a significant bit */ 66 a >>= 2; /* dump Q and R */ 67 /* a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits */ 68 if (a & ((tu_int)1 << LDBL_MANT_DIG)) 69 { 70 a >>= 1; 71 ++e; 72 } 73 /* a is now rounded to LDBL_MANT_DIG bits */ 74 } 75 else 76 { 77 a <<= (LDBL_MANT_DIG - sd); 78 /* a is now rounded to LDBL_MANT_DIG bits */ 79 } 80 long_double_bits fb; 81 fb.u.high.s.low = ((su_int)s & 0x8000) | /* sign */ 82 (e + 16383); /* exponent */ 83 fb.u.low.all = (du_int)a; /* mantissa */ 84 return fb.f; 85 } 86 87 #endif 88
