1214152Sed/* ===-- floatuntidf.c - Implement __floatuntidf ---------------------------=== 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 __floatuntidf for the compiler_rt library. 11214152Sed * 12214152Sed * ===----------------------------------------------------------------------=== 13214152Sed */ 14214152Sed 15239138Sandrew#include "int_lib.h" 16239138Sandrew 17263763Sdim#ifdef CRT_HAS_128BIT 18214152Sed 19214152Sed/* Returns: convert a to a double, rounding toward even. */ 20214152Sed 21214152Sed/* Assumption: double is a IEEE 64 bit floating point type 22214152Sed * tu_int is a 128 bit integral type 23214152Sed */ 24214152Sed 25214152Sed/* seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm */ 26214152Sed 27214152Sedsi_int __clzti2(ti_int a); 28214152Sed 29214152Seddouble 30214152Sed__floatuntidf(tu_int a) 31214152Sed{ 32214152Sed if (a == 0) 33214152Sed return 0.0; 34214152Sed const unsigned N = sizeof(tu_int) * CHAR_BIT; 35214152Sed int sd = N - __clzti2(a); /* number of significant digits */ 36214152Sed int e = sd - 1; /* exponent */ 37214152Sed if (sd > DBL_MANT_DIG) 38214152Sed { 39214152Sed /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 40214152Sed * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 41214152Sed * 12345678901234567890123456 42214152Sed * 1 = msb 1 bit 43214152Sed * P = bit DBL_MANT_DIG-1 bits to the right of 1 44214152Sed * Q = bit DBL_MANT_DIG bits to the right of 1 45214152Sed * R = "or" of all bits to the right of Q 46263763Sdim */ 47214152Sed switch (sd) 48214152Sed { 49214152Sed case DBL_MANT_DIG + 1: 50214152Sed a <<= 1; 51214152Sed break; 52214152Sed case DBL_MANT_DIG + 2: 53214152Sed break; 54214152Sed default: 55214152Sed a = (a >> (sd - (DBL_MANT_DIG+2))) | 56214152Sed ((a & ((tu_int)(-1) >> ((N + DBL_MANT_DIG+2) - sd))) != 0); 57214152Sed }; 58214152Sed /* finish: */ 59214152Sed a |= (a & 4) != 0; /* Or P into R */ 60214152Sed ++a; /* round - this step may add a significant bit */ 61214152Sed a >>= 2; /* dump Q and R */ 62214152Sed /* a is now rounded to DBL_MANT_DIG or DBL_MANT_DIG+1 bits */ 63214152Sed if (a & ((tu_int)1 << DBL_MANT_DIG)) 64214152Sed { 65214152Sed a >>= 1; 66214152Sed ++e; 67214152Sed } 68214152Sed /* a is now rounded to DBL_MANT_DIG bits */ 69214152Sed } 70214152Sed else 71214152Sed { 72214152Sed a <<= (DBL_MANT_DIG - sd); 73214152Sed /* a is now rounded to DBL_MANT_DIG bits */ 74214152Sed } 75214152Sed double_bits fb; 76214152Sed fb.u.s.high = ((e + 1023) << 20) | /* exponent */ 77214152Sed ((su_int)(a >> 32) & 0x000FFFFF); /* mantissa-high */ 78214152Sed fb.u.s.low = (su_int)a; /* mantissa-low */ 79214152Sed return fb.f; 80214152Sed} 81214152Sed 82263763Sdim#endif /* CRT_HAS_128BIT */ 83