1 /*===-- floatundisf.c - Implement __floatundisf ---------------------------=== 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 __floatundisf for the compiler_rt library. 11 * 12 *===----------------------------------------------------------------------=== 13 */ 14 15 #include "int_lib.h" 16 #include <float.h> 17 18 /* Returns: convert a to a float, rounding toward even. */ 19 20 /* Assumption: float is a IEEE 32 bit floating point type 21 * du_int is a 64 bit integral type 22 */ 23 24 /* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */ 25 26 float 27 __floatundisf(du_int a) 28 { 29 if (a == 0) 30 return 0.0F; 31 const unsigned N = sizeof(du_int) * CHAR_BIT; 32 int sd = N - __builtin_clzll(a); /* number of significant digits */ 33 int e = sd - 1; /* 8 exponent */ 34 if (sd > FLT_MANT_DIG) 35 { 36 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 37 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 38 * 12345678901234567890123456 39 * 1 = msb 1 bit 40 * P = bit FLT_MANT_DIG-1 bits to the right of 1 41 * Q = bit FLT_MANT_DIG bits to the right of 1 42 * R = "or" of all bits to the right of Q 43 */ 44 switch (sd) 45 { 46 case FLT_MANT_DIG + 1: 47 a <<= 1; 48 break; 49 case FLT_MANT_DIG + 2: 50 break; 51 default: 52 a = (a >> (sd - (FLT_MANT_DIG+2))) | 53 ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0); 54 }; 55 /* finish: */ 56 a |= (a & 4) != 0; /* Or P into R */ 57 ++a; /* round - this step may add a significant bit */ 58 a >>= 2; /* dump Q and R */ 59 /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */ 60 if (a & ((du_int)1 << FLT_MANT_DIG)) 61 { 62 a >>= 1; 63 ++e; 64 } 65 /* a is now rounded to FLT_MANT_DIG bits */ 66 } 67 else 68 { 69 a <<= (FLT_MANT_DIG - sd); 70 /* a is now rounded to FLT_MANT_DIG bits */ 71 } 72 float_bits fb; 73 fb.u = ((e + 127) << 23) | /* exponent */ 74 ((su_int)a & 0x007FFFFF); /* mantissa */ 75 return fb.f; 76 } 77
