libc/newlib/libm/common/s_lrint.c

/* @(#)s_lrint.c 5.1 93/09/24 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */
/*
FUNCTION
<<lrint>>, <<lrintf>>, <<llrint>>, <<llrintf>>---round to integer
INDEX
	lrint
INDEX
	lrintf
INDEX
	llrint
INDEX
	llrintf

SYNOPSIS
	#include <math.h>
	long int lrint(double <[x]>);
	long int lrintf(float <[x]>);
	long long int llrint(double <[x]>);
	long long int llrintf(float <[x]>);

DESCRIPTION
The <<lrint>> and <<llrint>> functions round their argument to the nearest
integer value, using the current rounding direction.  If the rounded value is
outside the range of the return type, the numeric result is unspecified.  A
range error may occur if the magnitude of <[x]> is too large.
The "inexact" floating-point exception is raised in implementations that
support it when the result differs in value from the argument (i.e., when
a fraction actually has been truncated).

RETURNS
<[x]> rounded to an integral value, using the current rounding direction.

SEEALSO
<<lround>>

PORTABILITY
ANSI C, POSIX

*/

/*
 * lrint(x)
 * Return x rounded to integral value according to the prevailing
 * rounding mode.
 * Method:
 *	Using floating addition.
 * Exception:
 *	Inexact flag raised if x not equal to lrint(x).
 */

#include "fdlibm.h"

#ifndef _DOUBLE_IS_32BITS

#ifdef __STDC__
static const double
#else
static double 
#endif

/* Adding a double, x, to 2^52 will cause the result to be rounded based on
   the fractional part of x, according to the implementation's current rounding
   mode.  2^52 is the smallest double that can be represented using all 52 significant
   digits. */
TWO52[2]={
  4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
};

#ifdef __STDC__
	long int lrint(double x)
#else
	long int lrint(x)
	double x;
#endif
{
  __int32_t i0,j0,sx;
  __uint32_t i1;
  double t;
  volatile double w;
  long int result;
  
  EXTRACT_WORDS(i0,i1,x);

  /* Extract sign bit. */
  sx = (i0>>31)&1;

  /* Extract exponent field. */
  j0 = ((i0 & 0x7ff00000) >> 20) - 1023;
  /* j0 in [-1023,1024] */
  
  if(j0 < 20)
    {
      /* j0 in [-1023,19] */
      if(j0 < -1)
        return 0;
      else
        {
          /* j0 in [0,19] */
	  /* shift amt in [0,19] */
          w = TWO52[sx] + x;
          t = w - TWO52[sx];
          GET_HIGH_WORD(i0, t);
          /* Detect the all-zeros representation of plus and
             minus zero, which fails the calculation below. */
          if ((i0 & ~(1L << 31)) == 0)
              return 0;
          /* After round:  j0 in [0,20] */
          j0 = ((i0 & 0x7ff00000) >> 20) - 1023;
          i0 &= 0x000fffff;
          i0 |= 0x00100000;
	  /* shift amt in [20,0] */
          result = i0 >> (20 - j0);
        }
    }
  else if (j0 < (int)(8 * sizeof (long int)) - 1)
    {
      /* 32bit return: j0 in [20,30] */
      /* 64bit return: j0 in [20,62] */
      if (j0 >= 52)
	/* 64bit return: j0 in [52,62] */
	/* 64bit return: left shift amt in [32,42] */
        result = ((long int) ((i0 & 0x000fffff) | 0x00100000) << (j0 - 20)) |
		/* 64bit return: right shift amt in [0,10] */
                   ((long int) i1 << (j0 - 52));
      else
        {
	  /* 32bit return: j0 in [20,30] */
	  /* 64bit return: j0 in [20,51] */
          w = TWO52[sx] + x;
          t = w - TWO52[sx];
          EXTRACT_WORDS (i0, i1, t);
          j0 = ((i0 & 0x7ff00000) >> 20) - 1023;
          i0 &= 0x000fffff;
          i0 |= 0x00100000;
          /* After round:
	   * 32bit return: j0 in [20,31];
	   * 64bit return: j0 in [20,52] */
	  /* 32bit return: left shift amt in [0,11] */
	  /* 64bit return: left shift amt in [0,32] */
          /* ***32bit return: right shift amt in [32,21] */
          /* ***64bit return: right shift amt in [32,0] */
          result = ((long int) i0 << (j0 - 20))
			| SAFE_RIGHT_SHIFT (i1, (52 - j0));
        }
    }
  else
    {
      return (long int) x;
    }
  
  return sx ? -result : result;
}

#endif /* _DOUBLE_IS_32BITS */