#include <limits.h> #include <math.h> typedef union { struct { #if defined(__BIG_ENDIAN__) unsigned long int hi; unsigned long int lo; #else unsigned long int lo; unsigned long int hi; #endif } words; double dbl; } DblInHex; static const unsigned long int signMask = 0x80000000ul; static const double twoTo52 = 4503599627370496.0; /******************************************************************************* * * * The function round rounds its double argument to integral value * * according to the "add half to the magnitude and truncate" rounding of * * Pascal's Round function and FORTRAN's ANINT function and returns the * * result in double format. This function signals inexact if an ordered * * return value is not equal to the operand. * * * *******************************************************************************/ double round ( double x ) { DblInHex argument, OldEnvironment; register double y, z; register unsigned long int xHead; register long int target; argument.dbl = x; xHead = argument.words.hi & 0x7fffffffUL; // xHead <- high half of |x| target = ( argument.words.hi < signMask ); // flag positive sign if ( xHead < 0x43300000ul ) /******************************************************************************* * Is |x| < 2.0^52? * *******************************************************************************/ { if ( xHead < 0x3ff00000ul ) /******************************************************************************* * Is |x| < 1.0? * *******************************************************************************/ { asm ("mffs %0" : "=f" (OldEnvironment.dbl)); // get environment if ( xHead < 0x3fe00000ul ) /******************************************************************************* * Is |x| < 0.5? * *******************************************************************************/ { if ( ( xHead | argument.words.lo ) != 0ul ) OldEnvironment.words.lo |= 0x02000000ul; asm ("mtfsf 255,%0" : /*NULLOUT*/ : /*IN*/ "f" ( OldEnvironment.dbl )); if ( target ) return ( 0.0 ); else return ( -0.0 ); } /******************************************************************************* * Is 0.5 � |x| < 1.0? * *******************************************************************************/ OldEnvironment.words.lo |= 0x02000000ul; asm ("mtfsf 255,%0" : /*NULLOUT*/ : /*IN*/ "f" ( OldEnvironment.dbl )); if ( target ) return ( 1.0 ); else return ( -1.0 ); } /******************************************************************************* * Is 1.0 < |x| < 2.0^52? * *******************************************************************************/ if ( target ) { // positive x y = ( x + twoTo52 ) - twoTo52; // round at binary point if ( y == x ) // exact case return ( x ); z = x + 0.5; // inexact case y = ( z + twoTo52 ) - twoTo52; // round at binary point if ( y > z ) return ( y - 1.0 ); else return ( y ); } /******************************************************************************* * Is x < 0? * *******************************************************************************/ else { y = ( x - twoTo52 ) + twoTo52; // round at binary point if ( y == x ) return ( x ); z = x - 0.5; y = ( z - twoTo52 ) + twoTo52; // round at binary point if ( y < z ) return ( y + 1.0 ); else return ( y ); } } /******************************************************************************* * |x| >= 2.0^52 or x is a NaN. * *******************************************************************************/ return ( x ); }