1 /* ===-- floatuntixf.c - Implement __floatuntixf ---------------------------=== 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 __floatuntixf 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 * tu_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 __floatuntixf(tu_int a) 34 { 35 if (a == 0) 36 return 0.0; 37 const unsigned N = sizeof(tu_int) * CHAR_BIT; 38 int sd = N - __clzti2(a); /* number of significant digits */ 39 int e = sd - 1; /* exponent */ 40 if (sd > LDBL_MANT_DIG) 41 { 42 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 43 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 44 * 12345678901234567890123456 45 * 1 = msb 1 bit 46 * P = bit LDBL_MANT_DIG-1 bits to the right of 1 47 * Q = bit LDBL_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 LDBL_MANT_DIG + 1: 53 a <<= 1; 54 break; 55 case LDBL_MANT_DIG + 2: 56 break; 57 default: 58 a = (a >> (sd - (LDBL_MANT_DIG+2))) | 59 ((a & ((tu_int)(-1) >> ((N + LDBL_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 LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits */ 66 if (a & ((tu_int)1 << LDBL_MANT_DIG)) 67 { 68 a >>= 1; 69 ++e; 70 } 71 /* a is now rounded to LDBL_MANT_DIG bits */ 72 } 73 else 74 { 75 a <<= (LDBL_MANT_DIG - sd); 76 /* a is now rounded to LDBL_MANT_DIG bits */ 77 } 78 long_double_bits fb; 79 fb.u.high.s.low = (e + 16383); /* exponent */ 80 fb.u.low.all = (du_int)a; /* mantissa */ 81 return fb.f; 82 } 83 84 #endif 85
