win/include/xpcom/nsMathUtils.h

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 * The Original Code is Mozilla Foundation code.
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 *   Stuart Parmenter <stuart@mozilla.com>
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#ifndef nsMathUtils_h__
#define nsMathUtils_h__

#include "nscore.h"
#include <math.h>
#include <float.h>

/*
 * round
 */
inline NS_HIDDEN_(double) NS_round(double x)
{
    return x >= 0.0 ? floor(x + 0.5) : ceil(x - 0.5);
}
inline NS_HIDDEN_(float) NS_roundf(float x)
{
    return x >= 0.0f ? floorf(x + 0.5f) : ceilf(x - 0.5f);
}
inline NS_HIDDEN_(PRInt32) NS_lround(double x)
{
    return x >= 0.0 ? PRInt32(x + 0.5) : PRInt32(x - 0.5);
}

/* NS_roundup30 rounds towards infinity for positive and       */
/* negative numbers.                                           */

#if defined(XP_WIN32) && defined(_M_IX86) && !defined(__GNUC__)
inline NS_HIDDEN_(PRInt32) NS_lroundup30(float x)
{
    /* Code derived from Laurent de Soras' paper at             */
    /* http://ldesoras.free.fr/doc/articles/rounding_en.pdf     */

    /* Rounding up on Windows is expensive using the float to   */
    /* int conversion and the floor function. A faster          */
    /* approach is to use f87 rounding while assuming the       */
    /* default rounding mode of rounding to the nearest         */
    /* integer. This rounding mode, however, actually rounds    */
    /* to the nearest integer so we add the floating point      */
    /* number to itself and add our rounding factor before      */
    /* doing the conversion to an integer. We then do a right   */
    /* shift of one bit on the integer to divide by two.        */

    /* This routine doesn't handle numbers larger in magnitude  */
    /* than 2^30 but this is fine for NSToCoordRound because    */
    /* Coords are limited to 2^30 in magnitude.                 */

    static const double round_to_nearest = 0.5f;
    int i;

    __asm {
      fld     x                   ; load fp argument
      fadd    st, st(0)           ; double it
      fadd    round_to_nearest    ; add the rounding factor
      fistp   dword ptr i         ; convert the result to int
    }
    return i >> 1;                /* divide by 2 */
}
#endif /* XP_WIN32 && _M_IX86 && !__GNUC__ */

inline NS_HIDDEN_(PRInt32) NS_lroundf(float x)
{
    return x >= 0.0f ? PRInt32(x + 0.5f) : PRInt32(x - 0.5f);
}

/*
 * ceil
 */
inline NS_HIDDEN_(double) NS_ceil(double x)
{
    return ceil(x);
}
inline NS_HIDDEN_(float) NS_ceilf(float x)
{
    return ceilf(x);
}

/*
 * floor
 */
inline NS_HIDDEN_(double) NS_floor(double x)
{
    return floor(x);
}
inline NS_HIDDEN_(float) NS_floorf(float x)
{
    return floorf(x);
}

#endif