i386/src/exp2f.s

	exp2f.s revision 25c28e83beb90e7c80452a7c818c5e6f73a07dc8
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
 */
/*
 * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

        .file "exp2f.s"

#include "libm.h"
LIBM_ANSI_PRAGMA_WEAK(exp2f,function)
#include "libm_synonyms.h"

    ENTRY(exp2f)
    movl    4(%esp),%ecx        / ecx <-- x
    andl    $0x7fffffff,%ecx    / ecx <-- |x|
    cmpl    $0x3f800000,%ecx    / Is |x| <= 1?
    jbe .shortcut       / If so, take a shortcut.
    cmpl    $0x7f800000,%ecx    / |x| >= INF?
    jae .not_finite     / if so, x is not finite
    flds    4(%esp)         / push arg
    fld %st(0)          / duplicate stack top
    frndint             / [x],x
    fucom               / x integral?
    fstsw   %ax
    sahf
    je      .x_integral     / branch if x integral
    fxch                / x, [x]
    fsub    %st(1),%st      / x-[x], [x]
    f2xm1               / 2**(x-[x])-1, [x]
    fld1                / 1,2**(x-[x])-1, [x]
    faddp   %st,%st(1)      / 2**(x-[x]), [x]
    fscale              / 2**x = 2**(arg), [x]
    fstp    %st(1)
    ret

.x_integral:                / here, x is integral
    fstp    %st(0)          / ,x
    fld1                / 1 = 2**0, x
    fscale              / 2**(0 + x) = 2**x, x
    fstp    %st(1)          / 2**x
    ret

.shortcut:
    / Here, |x| <= 1,
    / whence x is in f2xm1's domain.
    flds    4(%esp)         / push x
    f2xm1               / 2**x - 1
    fld1                / 1,2**x - 1
    faddp   %st,%st(1)      / 2**x
    ret

.not_finite:
    ja  .NaN_or_pinf        / branch if x is NaN
    movl    4(%esp),%eax        / eax <-- x
    andl    $0x80000000,%eax    / here, x is infinite, but +/-?
    jz  .NaN_or_pinf        / branch if x = +INF
    fldz                / Here, x = -inf, so return 0
    ret

.NaN_or_pinf:
    / Here, x = NaN or +inf, so load x and return immediately.
    flds    4(%esp)
    fwait
    ret
    .align  4
    SET_SIZE(exp2f)