usr/src/lib/libm/common/C/fmod.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  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
  23  */
  24 /*
  25  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
  26  * Use is subject to license terms.
  27  */
  28
  29 #pragma weak __fmod = fmod
  30
  31 #include "libm.h"
  32
  33 static const double zero = 0.0;
  34
  35 /*
  36  * The following implementation assumes fast 64-bit integer arith-
  37  * metic.  This is fine for sparc because we build libm in v8plus
  38  * mode.  It's also fine for sparcv9 and amd64, although we have
  39  * assembly code on amd64.  For x86, it would be better to use
  40  * 32-bit code, but we have assembly for x86, too.
  41  */
  42 double
  43 fmod(double x, double y) {
  44         double          w;
  45         long long       hx, ix, iy, iz;
  46         int             nd, k, ny;
  47
  48         hx = *(long long *)&x;
  49         ix = hx & ~0x8000000000000000ull;
  50         iy = *(long long *)&y & ~0x8000000000000000ull;
  51
  52         /* handle special cases */
  53         if (iy == 0ll)
  54                 return (_SVID_libm_err(x, y, 27));
  55
  56         if (ix >= 0x7ff0000000000000ll || iy > 0x7ff0000000000000ll)
  57                 return ((x * y) * zero);
  58
  59         if (ix <= iy)
  60                 return ((ix < iy)? x : x * zero);
  61
  62         /*
  63          * Set:
  64          *      ny = true exponent of y
  65          *      nd = true exponent of x minus true exponent of y
  66          *      ix = normalized significand of x
  67          *      iy = normalized significand of y
  68          */
  69         ny = iy >> 52;
  70         k = ix >> 52;
  71         if (ny == 0) {
  72                 /* y is subnormal, x could be normal or subnormal */
  73                 ny = 1;
  74                 while (iy < 0x0010000000000000ll) {
  75                         ny -= 1;
  76                         iy += iy;
  77                 }
  78                 nd = k - ny;
  79                 if (k == 0) {
  80                         nd += 1;
  81                         while (ix < 0x0010000000000000ll) {
  82                                 nd -= 1;
  83                                 ix += ix;
  84                         }
  85                 } else {
  86                         ix = 0x0010000000000000ll | (ix & 0x000fffffffffffffll);
  87                 }
  88         } else {
  89                 /* both x and y are normal */
  90                 nd = k - ny;
  91                 ix = 0x0010000000000000ll | (ix & 0x000fffffffffffffll);
  92                 iy = 0x0010000000000000ll | (iy & 0x000fffffffffffffll);
  93         }
  94
  95         /* perform fixed point mod */
  96         while (nd--) {
  97                 iz = ix - iy;
  98                 if (iz >= 0)
  99                         ix = iz;
 100                 ix += ix;
 101         }
 102         iz = ix - iy;
 103         if (iz >= 0)
 104                 ix = iz;
 105
 106         /* convert back to floating point and restore the sign */
 107         if (ix == 0ll)
 108                 return (x * zero);
 109         while (ix < 0x0010000000000000ll) {
 110                 ix += ix;
 111                 ny -= 1;
 112         }
 113         while (ix > 0x0020000000000000ll) {     /* XXX can this ever happen? */
 114                 ny += 1;
 115                 ix >>= 1;
 116         }
 117         if (ny <= 0) {
 118                 /* result is subnormal */
 119                 k = -ny + 1;
 120                 ix >>= k;
 121                 *(long long *)&w = (hx & 0x8000000000000000ull) | ix;
 122                 return (w);
 123         }
 124         *(long long *)&w = (hx & 0x8000000000000000ull) |
 125             ((long long)ny << 52) | (ix & 0x000fffffffffffffll);
 126         return (w);
 127 }