1 /*===-- floatdisf.c - Implement __floatdisf -------------------------------=== 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 __floatdisf 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 * di_int is a 64 bit integral type 22 */ 23 24 /* seee eeee emmm mmmm mmmm mmmm mmmm mmmm */ 25 26 float 27 __floatdisf(di_int a) 28 { 29 if (a == 0) 30 return 0.0F; 31 const unsigned N = sizeof(di_int) * CHAR_BIT; 32 const di_int s = a >> (N-1); 33 a = (a ^ s) - s; 34 int sd = N - __builtin_clzll(a); /* number of significant digits */ 35 int e = sd - 1; /* exponent */ 36 if (sd > FLT_MANT_DIG) 37 { 38 /* start: 0000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQxxxxxxxxxxxxxxxxxx 39 * finish: 000000000000000000000000000000000000001xxxxxxxxxxxxxxxxxxxxxxPQR 40 * 12345678901234567890123456 41 * 1 = msb 1 bit 42 * P = bit FLT_MANT_DIG-1 bits to the right of 1 43 * Q = bit FLT_MANT_DIG bits to the right of 1 44 * R = "or" of all bits to the right of Q 45 */ 46 switch (sd) 47 { 48 case FLT_MANT_DIG + 1: 49 a <<= 1; 50 break; 51 case FLT_MANT_DIG + 2: 52 break; 53 default: 54 a = ((du_int)a >> (sd - (FLT_MANT_DIG+2))) | 55 ((a & ((du_int)(-1) >> ((N + FLT_MANT_DIG+2) - sd))) != 0); 56 }; 57 /* finish: */ 58 a |= (a & 4) != 0; /* Or P into R */ 59 ++a; /* round - this step may add a significant bit */ 60 a >>= 2; /* dump Q and R */ 61 /* a is now rounded to FLT_MANT_DIG or FLT_MANT_DIG+1 bits */ 62 if (a & ((du_int)1 << FLT_MANT_DIG)) 63 { 64 a >>= 1; 65 ++e; 66 } 67 /* a is now rounded to FLT_MANT_DIG bits */ 68 } 69 else 70 { 71 a <<= (FLT_MANT_DIG - sd); 72 /* a is now rounded to FLT_MANT_DIG bits */ 73 } 74 float_bits fb; 75 fb.u = ((su_int)s & 0x80000000) | /* sign */ 76 ((e + 127) << 23) | /* exponent */ 77 ((su_int)a & 0x007FFFFF); /* mantissa */ 78 return fb.f; 79 } 80
