1 /* ===-- floattixf.c - Implement __floattixf -------------------------------=== 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 __floattixf for the compiler_rt library. 11 * 12 * ===----------------------------------------------------------------------=== 13 */ 14 15 #include "int_lib.h" 16 17 #if __x86_64 18 19 /* Returns: convert a to a long double, rounding toward even. */ 20 21 /* Assumption: long double is a IEEE 80 bit floating point type padded to 128 bits 22 * ti_int is a 128 bit integral type 23 */ 24 25 /* gggg gggg gggg gggg gggg gggg gggg gggg | gggg gggg gggg gggg seee eeee eeee eeee | 26 * 1mmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm 27 */ 28 29 si_int __clzti2(ti_int a); 30 31 long double 32 __floattixf(ti_int a) 33 { 34 if (a == 0) 35 return 0.0; 36 const unsigned N = sizeof(ti_int) * CHAR_BIT; 37 const ti_int s = a >> (N-1); 38 a = (a ^ s) - s; 39 int sd = N - __clzti2(a); /* number of significant digits */ 40 int e = sd - 1; /* exponent */ 41 if (sd > LDBL_MANT_DIG) 42 { 43 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 44 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 45 * 12345678901234567890123456 46 * 1 = msb 1 bit 47 * P = bit LDBL_MANT_DIG-1 bits to the right of 1 48 * Q = bit LDBL_MANT_DIG bits to the right of 1 49 * R = "or" of all bits to the right of Q 50 */ 51 switch (sd) 52 { 53 case LDBL_MANT_DIG + 1: 54 a <<= 1; 55 break; 56 case LDBL_MANT_DIG + 2: 57 break; 58 default: 59 a = ((tu_int)a >> (sd - (LDBL_MANT_DIG+2))) | 60 ((a & ((tu_int)(-1) >> ((N + LDBL_MANT_DIG+2) - sd))) != 0); 61 }; 62 /* finish: */ 63 a |= (a & 4) != 0; /* Or P into R */ 64 ++a; /* round - this step may add a significant bit */ 65 a >>= 2; /* dump Q and R */ 66 /* a is now rounded to LDBL_MANT_DIG or LDBL_MANT_DIG+1 bits */ 67 if (a & ((tu_int)1 << LDBL_MANT_DIG)) 68 { 69 a >>= 1; 70 ++e; 71 } 72 /* a is now rounded to LDBL_MANT_DIG bits */ 73 } 74 else 75 { 76 a <<= (LDBL_MANT_DIG - sd); 77 /* a is now rounded to LDBL_MANT_DIG bits */ 78 } 79 long_double_bits fb; 80 fb.u.high.s.low = ((su_int)s & 0x8000) | /* sign */ 81 (e + 16383); /* exponent */ 82 fb.u.low.all = (du_int)a; /* mantissa */ 83 return fb.f; 84 } 85 86 #endif 87
