lib/libm/arch/x86_64/ldexp.c

   1 /*-
   2  * Copyright (c) 1990, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * This code is derived from software contributed to Berkeley by
   6  * Sean Eric Fagan.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. All advertising materials mentioning features or use of this software
  17  *    must display the following acknowledgement:
  18  *      This product includes software developed by the University of
  19  *      California, Berkeley and its contributors.
  20  * 4. Neither the name of the University nor the names of its contributors
  21  *    may be used to endorse or promote products derived from this software
  22  *    without specific prior written permission.
  23  *
  24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  34  * SUCH DAMAGE.
  35  *
  36  * $FreeBSD: src/lib/libc/i386/gen/ldexp.c,v 1.6 1999/08/27 23:59:21 peter Exp $
  37  */
  38
  39 #if defined(LIBC_RCS) && !defined(lint)
  40 static const char rcsid[] = "$FreeBSD: src/lib/libc/i386/gen/ldexp.c,v 1.6 1999/08/27 23:59:21 peter Exp $";
  41 #endif /* LIBC_RCS and not lint */
  42
  43 #include "mathimpl.h"
  44
  45 /*
  46  * ldexp(value, exp): return value * (2 ** exp).
  47  *
  48  * Written by Sean Eric Fagan (sef@kithrup.COM)
  49  * Sun Mar 11 20:27:09 PST 1990
  50  */
  51
  52 /*
  53  * We do the conversion in C to let gcc optimize it away, if possible.
  54  * The "fxch ; fstp" stuff is because value is still on the stack
  55  * (stupid 8087!).
  56  */
  57 double
  58 ldexp (double value, int exp)
  59 {
  60         double temp, texp, temp2;
  61         texp = exp;
  62 #ifdef __GNUC__
  63 #if    __GNUC__ >= 2
  64         asm ("fscale "
  65                 : "=u" (temp2), "=t" (temp)
  66                 : "0" (texp), "1" (value));
  67 #else
  68         asm ("fscale ; fxch %%st(1) ; fstp%L1 %1 "
  69                 : "=f" (temp), "=0" (temp2)
  70                 : "0" (texp), "f" (value));
  71 #endif
  72 #else
  73 error unknown asm
  74 #endif
  75         return (temp);
  76 }