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         .file "exp2.s"
  30 
  31 #include "libm.h"
  32 LIBM_ANSI_PRAGMA_WEAK(exp2,function)
  33 
  34         ENTRY(exp2)
  35         movl    8(%esp),%ecx            / ecx <-- hi_32(x)
  36         andl    $0x7fffffff,%ecx        / ecx <-- hi_32(|x|)
  37         cmpl    $0x3ff00000,%ecx        / Is |x| < 1?
  38         jb      .shortcut               / If so, take a shortcut.
  39         je      .check_tail             / |x| may be only slightly < ln(2)
  40         cmpl    $0x7ff00000,%ecx        / hi_32(|x|) >= hi_32(INF)?
  41         jae     .not_finite             / if so, x is not finite
  42 .finite_non_special:                    / Here, 1 < |x| < INF
  43         fldl    4(%esp)                 / push arg
  44         fld     %st(0)                  / duplicate stack top
  45         frndint                         / [x],x
  46         fucom                           / x integral?
  47         fstsw   %ax
  48         sahf
  49         je      .x_integral             / branch if x integral
  50         fxch                            / x, [x]
  51         fsub    %st(1),%st              / x-[x], [x]
  52         f2xm1                           / 2**(x-[x])-1, [x]
  53         fld1                            / 1,2**(x-[x])-1, [x]
  54         faddp   %st,%st(1)              / 2**(x-[x]), [x]
  55         fscale                          / 2**x = 2**(arg), [x]
  56         fstp    %st(1)
  57         ret
  58 
  59 .x_integral:
  60         fstp    %st(0)                  / ,x
  61         fld1                            / 1 = 2**0, x
  62         fscale                          / 2**(0 + x) = 2**x, x
  63         fstp    %st(1)                  / 2**x
  64         ret
  65 
  66 .check_tail:
  67         movl    4(%esp),%edx            / edx <-- lo_32(x)
  68         cmpl    $0x00000000,%edx        / Is |x| slightly > 1?
  69         ja      .finite_non_special     / branch if |x| slightly > 1
  70 .shortcut:
  71         / Here, |x| <= 1,
  72         / whence x is in f2xm1's domain.
  73         fldl    4(%esp)                 / push x
  74         f2xm1                           / 2**x - 1
  75         fld1                            / 1,2**x - 1
  76         faddp   %st,%st(1)              / 2**x
  77         ret
  78 
  79 .not_finite:
  80         cmpl    $0x7ff00000,%ecx        / hi_32(|x|) > hi_32(INF)?
  81         ja      .NaN_or_pinf            / if so, x is NaN 
  82         movl    4(%esp),%edx            / edx <-- lo_32(x)
  83         cmpl    $0,%edx                 / lo_32(x) = 0?
  84         jne     .NaN_or_pinf            / if not, x is NaN
  85         movl    8(%esp),%eax            / eax <-- hi_32(x)
  86         andl    $0x80000000,%eax        / here, x is infinite, but +/-?
  87         jz      .NaN_or_pinf            / branch if x = +INF
  88         fldz                            / Here, x = -inf, so return 0
  89         ret
  90 
  91 .NaN_or_pinf:
  92         / Here, x = NaN or +inf, so load x and return immediately.
  93         fldl    4(%esp)
  94         fwait
  95         ret
  96         .align  4
  97         SET_SIZE(exp2)