1 /* @(#)s_floor.c 5.1 93/09/24 */ 2 /* 3 * ==================================================== 4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 5 * 6 * Developed at SunPro, a Sun Microsystems, Inc. business. 7 * Permission to use, copy, modify, and distribute this 8 * software is freely granted, provided that this notice 9 * is preserved. 10 * ==================================================== 11 */ 12 13 #ifndef lint 14 static char rcsid[] = "$Id: s_floor.c,v 1.4 1994/03/03 17:04:35 jtc Exp $"; 15 #endif 16 17 /* 18 * floor(x) 19 * Return x rounded toward -inf to integral value 20 * Method: 21 * Bit twiddling. 22 * Exception: 23 * Inexact flag raised if x not equal to floor(x). 24 */ 25 26 #include <math.h> 27 #include <machine/endian.h> 28 29 #if BYTE_ORDER == LITTLE_ENDIAN 30 #define n0 1 31 #else 32 #define n0 0 33 #endif 34 35 #ifdef __STDC__ 36 static const double huge = 1.0e300; 37 #else 38 static double huge = 1.0e300; 39 #endif 40 41 #ifdef __STDC__ 42 double floor(double x) 43 #else 44 double floor(x) 45 double x; 46 #endif 47 { 48 int i0,i1,j0; 49 unsigned i,j; 50 i0 = *(n0+(int*)&x); 51 i1 = *(1-n0+(int*)&x); 52 j0 = ((i0>>20)&0x7ff)-0x3ff; 53 if(j0<20) { 54 if(j0<0) { /* raise inexact if x != 0 */ 55 if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */ 56 if(i0>=0) {i0=i1=0;} 57 else if(((i0&0x7fffffff)|i1)!=0) 58 { i0=0xbff00000;i1=0;} 59 } 60 } else { 61 i = (0x000fffff)>>j0; 62 if(((i0&i)|i1)==0) return x; /* x is integral */ 63 if(huge+x>0.0) { /* raise inexact flag */ 64 if(i0<0) i0 += (0x00100000)>>j0; 65 i0 &= (~i); i1=0; 66 } 67 } 68 } else if (j0>51) { 69 if(j0==0x400) return x+x; /* inf or NaN */ 70 else return x; /* x is integral */ 71 } else { 72 i = ((unsigned)(0xffffffff))>>(j0-20); 73 if((i1&i)==0) return x; /* x is integral */ 74 if(huge+x>0.0) { /* raise inexact flag */ 75 if(i0<0) { 76 if(j0==20) i0+=1; 77 else { 78 j = i1+(1<<(52-j0)); 79 if(j<i1) i0 +=1 ; /* got a carry */ 80 i1=j; 81 } 82 } 83 i1 &= (~i); 84 } 85 } 86 *(n0+(int*)&x) = i0; 87 *(1-n0+(int*)&x) = i1; 88 return x; 89 } 90