1 /* ===-- floatuntisf.c - Implement __floatuntisf ---------------------------=== 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 __floatuntisf for the compiler_rt library. 11 * 12 * ===----------------------------------------------------------------------=== 13 */ 14 15 #include "int_lib.h" 16 17 #ifdef CRT_HAS_128BIT 18 19 /* Returns: convert a to a float, rounding toward even. */ 20 21 /* Assumption: float is a IEEE 32 bit floating point type 22 * tu_int is a 128 bit integral type 23 */ 24 25 /* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */ 26 27 COMPILER_RT_ABI float 28 __floatuntisf(tu_int a) 29 { 30 if (a == 0) 31 return 0.0F; 32 const unsigned N = sizeof(tu_int) * CHAR_BIT; 33 int sd = N - __clzti2(a); /* number of significant digits */ 34 int e = sd - 1; /* exponent */ 35 if (sd > FLT_MANT_DIG) 36 { 37 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 38 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 39 * 12345678901234567890123456 40 * 1 = msb 1 bit 41 * P = bit FLT_MANT_DIG-1 bits to the right of 1 42 * Q = bit FLT_MANT_DIG bits to the right of 1 43 * R = "or" of all bits to the right of Q 44 */ 45 switch (sd) 46 { 47 case FLT_MANT_DIG + 1: 48 a <<= 1; 49 break; 50 case FLT_MANT_DIG + 2: 51 break; 52 default: 53 a = (a >> (sd - (FLT_MANT_DIG+2))) | 54 ((a & ((tu_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0); 55 }; 56 /* finish: */ 57 a |= (a & 4) != 0; /* Or P into R */ 58 ++a; /* round - this step may add a significant bit */ 59 a >>= 2; /* dump Q and R */ 60 /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */ 61 if (a & ((tu_int)1 << FLT_MANT_DIG)) 62 { 63 a >>= 1; 64 ++e; 65 } 66 /* a is now rounded to FLT_MANT_DIG bits */ 67 } 68 else 69 { 70 a <<= (FLT_MANT_DIG - sd); 71 /* a is now rounded to FLT_MANT_DIG bits */ 72 } 73 float_bits fb; 74 fb.u = ((e + 127) << 23) | /* exponent */ 75 ((su_int)a & 0x007FFFFF); /* mantissa */ 76 return fb.f; 77 } 78 79 #endif /* CRT_HAS_128BIT */ 80
