usr/src/lib/libm/common/m9x/llrint.c

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21
  22 /*
  23  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
  24  */
  25 /*
  26  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
  27  * Use is subject to license terms.
  28  */
  29
  30 #pragma weak __llrint = llrint
  31 #if defined(__sparcv9) || defined(__amd64)
  32 #pragma weak lrint = llrint
  33 #pragma weak __lrint = llrint
  34 #endif
  35
  36 /*
  37  * llrint(x) rounds its argument to the nearest integer according
  38  * to the current rounding direction and converts the result to a
  39  * 64 bit signed integer.
  40  *
  41  * If x is NaN, infinite, or so large that the nearest integer would
  42  * exceed 64 bits, the invalid operation exception is raised.  If x
  43  * is not an integer, the inexact exception is raised.
  44  */
  45
  46 #include "libm.h"
  47
  48 long long
  49 llrint(double x) {
  50         /*
  51          * Note: The following code works on x86 (in the default rounding
  52          * precision mode), but one should just use the fistpll instruction
  53          * instead.
  54          */
  55         union {
  56                 unsigned i[2];
  57                 double d;
  58         } xx, yy;
  59         unsigned hx;
  60
  61         xx.d = x;
  62         hx = xx.i[HIWORD] & ~0x80000000;
  63
  64         if (hx < 0x43300000) { /* |x| < 2^52 */
  65                 /* add and subtract a power of two to round x to an integer */
  66 #if defined(__sparc) || defined(__amd64)
  67                 yy.i[HIWORD] = (xx.i[HIWORD] & 0x80000000) | 0x43300000;
  68 #elif defined(__i386)   /* !defined(__amd64) */
  69                 yy.i[HIWORD] = (xx.i[HIWORD] & 0x80000000) | 0x43e00000;
  70 #else
  71 #error Unknown architecture
  72 #endif
  73                 yy.i[LOWORD] = 0;
  74                 x = (x + yy.d) - yy.d;
  75         }
  76
  77         /* now x is nan, inf, or integral */
  78         return ((long long) x);
  79 }