floattidf.c revision 222656
1214152Sed/* ===-- floattidf.c - Implement __floattidf -------------------------------=== 2214152Sed * 3214152Sed * The LLVM Compiler Infrastructure 4214152Sed * 5222656Sed * This file is dual licensed under the MIT and the University of Illinois Open 6222656Sed * Source Licenses. See LICENSE.TXT for details. 7214152Sed * 8214152Sed * ===----------------------------------------------------------------------=== 9214152Sed * 10214152Sed * This file implements __floattidf for the compiler_rt library. 11214152Sed * 12214152Sed * ===----------------------------------------------------------------------=== 13214152Sed */ 14214152Sed 15214152Sed#if __x86_64 16214152Sed 17214152Sed#include "int_lib.h" 18214152Sed#include <float.h> 19214152Sed 20214152Sed/* Returns: convert a to a double, rounding toward even.*/ 21214152Sed 22214152Sed/* Assumption: double is a IEEE 64 bit floating point type 23214152Sed * ti_int is a 128 bit integral type 24214152Sed */ 25214152Sed 26214152Sed/* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */ 27214152Sed 28214152Sedsi_int __clzti2(ti_int a); 29214152Sed 30214152Seddouble 31214152Sed__floattidf(ti_int a) 32214152Sed{ 33214152Sed if (a == 0) 34214152Sed return 0.0; 35214152Sed const unsigned N = sizeof(ti_int) * CHAR_BIT; 36214152Sed const ti_int s = a >> (N-1); 37214152Sed a = (a ^ s) - s; 38214152Sed int sd = N - __clzti2(a); /* number of significant digits */ 39214152Sed int e = sd - 1; /* exponent */ 40214152Sed if (sd > DBL_MANT_DIG) 41214152Sed { 42214152Sed /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 43214152Sed * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 44214152Sed * 12345678901234567890123456 45214152Sed * 1 = msb 1 bit 46214152Sed * P = bit DBL_MANT_DIG-1 bits to the right of 1 47214152Sed * Q = bit DBL_MANT_DIG bits to the right of 1 48214152Sed * R = "or" of all bits to the right of Q 49214152Sed */ 50214152Sed switch (sd) 51214152Sed { 52214152Sed case DBL_MANT_DIG + 1: 53214152Sed a <<= 1; 54214152Sed break; 55214152Sed case DBL_MANT_DIG + 2: 56214152Sed break; 57214152Sed default: 58214152Sed a = ((tu_int)a >> (sd - (DBL_MANT_DIG+2))) | 59214152Sed ((a & ((tu_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0); 60214152Sed }; 61214152Sed /* finish: */ 62214152Sed a |= (a & 4) != 0; /* Or P into R */ 63214152Sed ++a; /* round - this step may add a significant bit */ 64214152Sed a >>= 2; /* dump Q and R */ 65214152Sed /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */ 66214152Sed if (a & ((tu_int)1 << DBL_MANT_DIG)) 67214152Sed { 68214152Sed a >>= 1; 69214152Sed ++e; 70214152Sed } 71214152Sed /* a is now rounded to DBL_MANT_DIG bits */ 72214152Sed } 73214152Sed else 74214152Sed { 75214152Sed a <<= (DBL_MANT_DIG - sd); 76214152Sed /* a is now rounded to DBL_MANT_DIG bits */ 77214152Sed } 78214152Sed double_bits fb; 79214152Sed fb.u.s.high = ((su_int)s & 0x80000000) | /* sign */ 80214152Sed ((e + 1023) << 20) | /* exponent */ 81214152Sed ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */ 82214152Sed fb.u.s.low = (su_int)a; /* mantissa-low */ 83214152Sed return fb.f; 84214152Sed} 85214152Sed 86214152Sed#endif 87