libm/amd64/fenv.c - platform/bionic - Git at Google

 /*  $OpenBSD: fenv.c,v 1.3 2012/12/05 23:20:02 deraadt Exp $  */
 /*  $NetBSD: fenv.c,v 1.1 2010/07/31 21:47:53 joerg Exp $ */

 /*-
  * Copyright (c) 2004-2005 David Schultz <das (at) FreeBSD.ORG>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */

 #include <fenv.h>
 #include <machine/fpu.h>

 #define SSE_MASK_SHIFT 7

 /*
  * The following symbol is simply the bitwise-inclusive OR of all floating-point
  * rounding direction constants defined above.
  */
 #define X87_ROUND_MASK  (FE_TONEAREST | FE_DOWNWARD | FE_UPWARD | FE_TOWARDZERO)
 #define SSE_ROUND_SHIFT 3

 /*
  * The following constant represents the default floating-point environment
  * (that is, the one installed at program startup) and has type pointer to
  * const-qualified fenv_t.
  *
  * It can be used as an argument to the functions within the <fenv.h> header
  * that manage the floating-point environment, namely fesetenv() and
  * feupdateenv().
  *
  * x87 fpu registers are 16bit wide. The upper bits, 31-16, are marked as
  * RESERVED.
  */
 const fenv_t __fe_dfl_env = {
   {
     0xffff0000 | __INITIAL_NPXCW__, /* Control word register */
     0xffff0000,                     /* Status word register */
     0xffffffff,                     /* Tag word register */
     {
       0x00000000,
       0x00000000,
       0x00000000,
       0xffff0000
     }
   },
   __INITIAL_MXCSR__                 /* MXCSR register */
 };


 /*
  * The feclearexcept() function clears the supported floating-point exceptions
  * represented by `excepts'.
  */
 int
 feclearexcept(int excepts)
 {
   fenv_t fenv;
   unsigned int mxcsr;

   excepts &= FE_ALL_EXCEPT;

   /* Store the current x87 floating-point environment */
   __asm__ __volatile__ ("fnstenv %0" : "=m" (fenv));

   /* Clear the requested floating-point exceptions */
   fenv.__x87.__status &= ~excepts;

   /* Load the x87 floating-point environent */
   __asm__ __volatile__ ("fldenv %0" : : "m" (fenv));

   /* Same for SSE environment */
   __asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));
   mxcsr &= ~excepts;
   __asm__ __volatile__ ("ldmxcsr %0" : : "m" (mxcsr));

   return (0);
 }

 /*
  * The fegetexceptflag() function stores an implementation-defined
  * representation of the states of the floating-point status flags indicated by
  * the argument excepts in the object pointed to by the argument flagp.
  */
 int
 fegetexceptflag(fexcept_t *flagp, int excepts)
 {
   unsigned short status;
   unsigned int mxcsr;

   excepts &= FE_ALL_EXCEPT;

   /* Store the current x87 status register */
   __asm__ __volatile__ ("fnstsw %0" : "=am" (status));

   /* Store the MXCSR register */
   __asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));

   /* Store the results in flagp */
   *flagp = (status | mxcsr) & excepts;

   return (0);
 }

 /*
  * The feraiseexcept() function raises the supported floating-point exceptions
  * represented by the argument `excepts'.
  *
  * The standard explicitly allows us to execute an instruction that has the
  * exception as a side effect, but we choose to manipulate the status register
  * directly.
  *
  * The validation of input is being deferred to fesetexceptflag().
  */
 int
 feraiseexcept(int excepts)
 {
   excepts &= FE_ALL_EXCEPT;

   fesetexceptflag((fexcept_t *)&excepts, excepts);
   __asm__ __volatile__ ("fwait");

   return (0);
 }

 /*
  * This function sets the floating-point status flags indicated by the argument
  * `excepts' to the states stored in the object pointed to by `flagp'. It does
  * NOT raise any floating-point exceptions, but only sets the state of the flags.
  */
 int
 fesetexceptflag(const fexcept_t *flagp, int excepts)
 {
   fenv_t fenv;
   unsigned int mxcsr;

   excepts &= FE_ALL_EXCEPT;

   /* Store the current x87 floating-point environment */
   __asm__ __volatile__ ("fnstenv %0" : "=m" (fenv));

   /* Set the requested status flags */
   fenv.__x87.__status &= ~excepts;
   fenv.__x87.__status |= *flagp & excepts;

   /* Load the x87 floating-point environent */
   __asm__ __volatile__ ("fldenv %0" : : "m" (fenv));

   /* Same for SSE environment */
   __asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));
   mxcsr &= ~excepts;
   mxcsr |= *flagp & excepts;
   __asm__ __volatile__ ("ldmxcsr %0" : : "m" (mxcsr));

   return (0);
 }

 /*
  * The fetestexcept() function determines which of a specified subset of the
  * floating-point exception flags are currently set. The `excepts' argument
  * specifies the floating-point status flags to be queried.
  */
 int
 fetestexcept(int excepts)
 {
   unsigned short status;
   unsigned int mxcsr;

   excepts &= FE_ALL_EXCEPT;

   /* Store the current x87 status register */
   __asm__ __volatile__ ("fnstsw %0" : "=am" (status));

   /* Store the MXCSR register state */
   __asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));

   return ((status | mxcsr) & excepts);
 }

 /*
  * The fegetround() function gets the current rounding direction.
  */
 int
 fegetround(void)
 {
   unsigned short control;

   /*
    * We assume that the x87 and the SSE unit agree on the
    * rounding mode.  Reading the control word on the x87 turns
    * out to be about 5 times faster than reading it on the SSE
    * unit on an Opteron 244.
    */
   __asm__ __volatile__ ("fnstcw %0" : "=m" (control));

   return (control & X87_ROUND_MASK);
 }

 /*
  * The fesetround() function establishes the rounding direction represented by
  * its argument `round'. If the argument is not equal to the value of a rounding
  * direction macro, the rounding direction is not changed.
  */
 int
 fesetround(int round)
 {
   unsigned short control;
   unsigned int mxcsr;

   /* Check whether requested rounding direction is supported */
   if (round & ~X87_ROUND_MASK)
     return (-1);

   /* Store the current x87 control word register */
   __asm__ __volatile__ ("fnstcw %0" : "=m" (control));

   /* Set the rounding direction */
   control &= ~X87_ROUND_MASK;
   control |= round;

   /* Load the x87 control word register */
   __asm__ __volatile__ ("fldcw %0" : : "m" (control));

   /* Same for the SSE environment */
   __asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));
   mxcsr &= ~(X87_ROUND_MASK << SSE_ROUND_SHIFT);
   mxcsr |= round << SSE_ROUND_SHIFT;
   __asm__ __volatile__ ("ldmxcsr %0" : : "m" (mxcsr));

   return (0);
 }

 /*
  * The fegetenv() function attempts to store the current floating-point
  * environment in the object pointed to by envp.
  */
 int
 fegetenv(fenv_t *envp)
 {
   /* Store the current x87 floating-point environment */
   __asm__ __volatile__ ("fnstenv %0" : "=m" (*envp));

   /* Store the MXCSR register state */
   __asm__ __volatile__ ("stmxcsr %0" : "=m" (envp->__mxcsr));

   /*
    * When an FNSTENV instruction is executed, all pending exceptions are
    * essentially lost (either the x87 FPU status register is cleared or
    * all exceptions are masked).
    *
    * 8.6 X87 FPU EXCEPTION SYNCHRONIZATION -
    * Intel(R) 64 and IA-32 Architectures Softare Developer's Manual - Vol1
    */
   __asm__ __volatile__ ("fldcw %0" : : "m" (envp->__x87.__control));

   return (0);
 }

 /*
  * The feholdexcept() function saves the current floating-point environment
  * in the object pointed to by envp, clears the floating-point status flags, and
  * then installs a non-stop (continue on floating-point exceptions) mode, if
  * available, for all floating-point exceptions.
  */
 int
 feholdexcept(fenv_t *envp)
 {
   unsigned int mxcsr;

   /* Store the current x87 floating-point environment */
   __asm__ __volatile__ ("fnstenv %0" : "=m" (*envp));

   /* Clear all exception flags in FPU */
   __asm__ __volatile__ ("fnclex");

   /* Store the MXCSR register state */
   __asm__ __volatile__ ("stmxcsr %0" : "=m" (envp->__mxcsr));

   /* Clear exception flags in MXCSR */
   mxcsr = envp->__mxcsr;
   mxcsr &= ~FE_ALL_EXCEPT;

   /* Mask all exceptions */
   mxcsr |= FE_ALL_EXCEPT << SSE_MASK_SHIFT;

   /* Store the MXCSR register */
   __asm__ __volatile__ ("ldmxcsr %0" : : "m" (mxcsr));

   return (0);
 }

 /*
  * The fesetenv() function attempts to establish the floating-point environment
  * represented by the object pointed to by envp. The argument `envp' points
  * to an object set by a call to fegetenv() or feholdexcept(), or equal a
  * floating-point environment macro. The fesetenv() function does not raise
  * floating-point exceptions, but only installs the state of the floating-point
  * status flags represented through its argument.
  */
 int
 fesetenv(const fenv_t *envp)
 {
   /* Load the x87 floating-point environent */
   __asm__ __volatile__ ("fldenv %0" : : "m" (*envp));

   /* Store the MXCSR register */
   __asm__ __volatile__ ("ldmxcsr %0" : : "m" (envp->__mxcsr));

   return (0);
 }

 /*
  * The feupdateenv() function saves the currently raised floating-point
  * exceptions in its automatic storage, installs the floating-point environment
  * represented by the object pointed to by `envp', and then raises the saved
  * floating-point exceptions. The argument `envp' shall point to an object set
  * by a call to feholdexcept() or fegetenv(), or equal a floating-point
  * environment macro.
  */
 int
 feupdateenv(const fenv_t *envp)
 {
   unsigned short status;
   unsigned int mxcsr;

   /* Store the x87 status register */
   __asm__ __volatile__ ("fnstsw %0" : "=am" (status));

   /* Store the MXCSR register */
   __asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));

   /* Install new floating-point environment */
   fesetenv(envp);

   /* Raise any previously accumulated exceptions */
   feraiseexcept(status | mxcsr);

   return (0);
 }

 /*
  * The following functions are extentions to the standard
  */
 int
 feenableexcept(int mask)
 {
   unsigned int mxcsr, omask;
   unsigned short control;

   mask &= FE_ALL_EXCEPT;

   __asm__ __volatile__ ("fnstcw %0" : "=m" (control));
   __asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));

   omask = ~(control | (mxcsr >> SSE_MASK_SHIFT)) & FE_ALL_EXCEPT;
   control &= ~mask;
   __asm__ __volatile__ ("fldcw %0" : : "m" (control));

   mxcsr &= ~(mask << SSE_MASK_SHIFT);
   __asm__ __volatile__ ("ldmxcsr %0" : : "m" (mxcsr));

   return (omask);
 }

 int
 fedisableexcept(int mask)
 {
   unsigned int mxcsr, omask;
   unsigned short control;

   mask &= FE_ALL_EXCEPT;

   __asm__ __volatile__ ("fnstcw %0" : "=m" (control));
   __asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));

   omask = ~(control | (mxcsr >> SSE_MASK_SHIFT)) & FE_ALL_EXCEPT;
   control |= mask;
   __asm__ __volatile__ ("fldcw %0" : : "m" (control));

   mxcsr |= mask << SSE_MASK_SHIFT;
   __asm__ __volatile__ ("ldmxcsr %0" : : "m" (mxcsr));

   return (omask);
 }

 int
 fegetexcept(void)
 {
   unsigned short control;

   /*
    * We assume that the masks for the x87 and the SSE unit are
    * the same.
    */
   __asm__ __volatile__ ("fnstcw %0" : "=m" (control));

   return (~control & FE_ALL_EXCEPT);
 }
	/* $OpenBSD: fenv.c,v 1.3 2012/12/05 23:20:02 deraadt Exp $ */
	/* $NetBSD: fenv.c,v 1.1 2010/07/31 21:47:53 joerg Exp $ */

	/*-
	* Copyright (c) 2004-2005 David Schultz <das (at) FreeBSD.ORG>
	* All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	*
	* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	* SUCH DAMAGE.
	*/

	#include <fenv.h>
	#include <machine/fpu.h>

	#define SSE_MASK_SHIFT 7

	/*
	* The following symbol is simply the bitwise-inclusive OR of all floating-point
	* rounding direction constants defined above.
	*/
	#define X87_ROUND_MASK (FE_TONEAREST \| FE_DOWNWARD \| FE_UPWARD \| FE_TOWARDZERO)
	#define SSE_ROUND_SHIFT 3

	/*
	* The following constant represents the default floating-point environment
	* (that is, the one installed at program startup) and has type pointer to
	* const-qualified fenv_t.
	*
	* It can be used as an argument to the functions within the <fenv.h> header
	* that manage the floating-point environment, namely fesetenv() and
	* feupdateenv().
	*
	* x87 fpu registers are 16bit wide. The upper bits, 31-16, are marked as
	* RESERVED.
	*/
	const fenv_t __fe_dfl_env = {
	{
	0xffff0000 \| __INITIAL_NPXCW__, /* Control word register */
	0xffff0000, /* Status word register */
	0xffffffff, /* Tag word register */
	{
	0x00000000,
	0x00000000,
	0x00000000,
	0xffff0000
	}
	},
	__INITIAL_MXCSR__ /* MXCSR register */
	};


	/*
	* The feclearexcept() function clears the supported floating-point exceptions
	* represented by `excepts'.
	*/
	int
	feclearexcept(int excepts)
	{
	fenv_t fenv;
	unsigned int mxcsr;

	excepts &= FE_ALL_EXCEPT;

	/* Store the current x87 floating-point environment */
	__asm__ __volatile__ ("fnstenv %0" : "=m" (fenv));

	/* Clear the requested floating-point exceptions */
	fenv.__x87.__status &= ~excepts;

	/* Load the x87 floating-point environent */
	__asm__ __volatile__ ("fldenv %0" : : "m" (fenv));

	/* Same for SSE environment */
	__asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));
	mxcsr &= ~excepts;
	__asm__ __volatile__ ("ldmxcsr %0" : : "m" (mxcsr));

	return (0);
	}

	/*
	* The fegetexceptflag() function stores an implementation-defined
	* representation of the states of the floating-point status flags indicated by
	* the argument excepts in the object pointed to by the argument flagp.
	*/
	int
	fegetexceptflag(fexcept_t *flagp, int excepts)
	{
	unsigned short status;
	unsigned int mxcsr;

	excepts &= FE_ALL_EXCEPT;

	/* Store the current x87 status register */
	__asm__ __volatile__ ("fnstsw %0" : "=am" (status));

	/* Store the MXCSR register */
	__asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));

	/* Store the results in flagp */
	*flagp = (status \| mxcsr) & excepts;

	return (0);
	}

	/*
	* The feraiseexcept() function raises the supported floating-point exceptions
	* represented by the argument `excepts'.
	*
	* The standard explicitly allows us to execute an instruction that has the
	* exception as a side effect, but we choose to manipulate the status register
	* directly.
	*
	* The validation of input is being deferred to fesetexceptflag().
	*/
	int
	feraiseexcept(int excepts)
	{
	excepts &= FE_ALL_EXCEPT;

	fesetexceptflag((fexcept_t *)&excepts, excepts);
	__asm__ __volatile__ ("fwait");

	return (0);
	}

	/*
	* This function sets the floating-point status flags indicated by the argument
	* `excepts' to the states stored in the object pointed to by `flagp'. It does
	* NOT raise any floating-point exceptions, but only sets the state of the flags.
	*/
	int
	fesetexceptflag(const fexcept_t *flagp, int excepts)
	{
	fenv_t fenv;
	unsigned int mxcsr;

	excepts &= FE_ALL_EXCEPT;

	/* Store the current x87 floating-point environment */
	__asm__ __volatile__ ("fnstenv %0" : "=m" (fenv));

	/* Set the requested status flags */
	fenv.__x87.__status &= ~excepts;
	fenv.__x87.__status \|= *flagp & excepts;

	/* Load the x87 floating-point environent */
	__asm__ __volatile__ ("fldenv %0" : : "m" (fenv));

	/* Same for SSE environment */
	__asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));
	mxcsr &= ~excepts;
	mxcsr \|= *flagp & excepts;
	__asm__ __volatile__ ("ldmxcsr %0" : : "m" (mxcsr));

	return (0);
	}

	/*
	* The fetestexcept() function determines which of a specified subset of the
	* floating-point exception flags are currently set. The `excepts' argument
	* specifies the floating-point status flags to be queried.
	*/
	int
	fetestexcept(int excepts)
	{
	unsigned short status;
	unsigned int mxcsr;

	excepts &= FE_ALL_EXCEPT;

	/* Store the current x87 status register */
	__asm__ __volatile__ ("fnstsw %0" : "=am" (status));

	/* Store the MXCSR register state */
	__asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));

	return ((status \| mxcsr) & excepts);
	}

	/*
	* The fegetround() function gets the current rounding direction.
	*/
	int
	fegetround(void)
	{
	unsigned short control;

	/*
	* We assume that the x87 and the SSE unit agree on the
	* rounding mode. Reading the control word on the x87 turns
	* out to be about 5 times faster than reading it on the SSE
	* unit on an Opteron 244.
	*/
	__asm__ __volatile__ ("fnstcw %0" : "=m" (control));

	return (control & X87_ROUND_MASK);
	}

	/*
	* The fesetround() function establishes the rounding direction represented by
	* its argument `round'. If the argument is not equal to the value of a rounding
	* direction macro, the rounding direction is not changed.
	*/
	int
	fesetround(int round)
	{
	unsigned short control;
	unsigned int mxcsr;

	/* Check whether requested rounding direction is supported */
	if (round & ~X87_ROUND_MASK)
	return (-1);

	/* Store the current x87 control word register */
	__asm__ __volatile__ ("fnstcw %0" : "=m" (control));

	/* Set the rounding direction */
	control &= ~X87_ROUND_MASK;
	control \|= round;

	/* Load the x87 control word register */
	__asm__ __volatile__ ("fldcw %0" : : "m" (control));

	/* Same for the SSE environment */
	__asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));
	mxcsr &= ~(X87_ROUND_MASK << SSE_ROUND_SHIFT);
	mxcsr \|= round << SSE_ROUND_SHIFT;
	__asm__ __volatile__ ("ldmxcsr %0" : : "m" (mxcsr));

	return (0);
	}

	/*
	* The fegetenv() function attempts to store the current floating-point
	* environment in the object pointed to by envp.
	*/
	int
	fegetenv(fenv_t *envp)
	{
	/* Store the current x87 floating-point environment */
	__asm__ __volatile__ ("fnstenv %0" : "=m" (*envp));

	/* Store the MXCSR register state */
	__asm__ __volatile__ ("stmxcsr %0" : "=m" (envp->__mxcsr));

	/*
	* When an FNSTENV instruction is executed, all pending exceptions are
	* essentially lost (either the x87 FPU status register is cleared or
	* all exceptions are masked).
	*
	* 8.6 X87 FPU EXCEPTION SYNCHRONIZATION -
	* Intel(R) 64 and IA-32 Architectures Softare Developer's Manual - Vol1
	*/
	__asm__ __volatile__ ("fldcw %0" : : "m" (envp->__x87.__control));

	return (0);
	}

	/*
	* The feholdexcept() function saves the current floating-point environment
	* in the object pointed to by envp, clears the floating-point status flags, and
	* then installs a non-stop (continue on floating-point exceptions) mode, if
	* available, for all floating-point exceptions.
	*/
	int
	feholdexcept(fenv_t *envp)
	{
	unsigned int mxcsr;

	/* Store the current x87 floating-point environment */
	__asm__ __volatile__ ("fnstenv %0" : "=m" (*envp));

	/* Clear all exception flags in FPU */
	__asm__ __volatile__ ("fnclex");

	/* Store the MXCSR register state */
	__asm__ __volatile__ ("stmxcsr %0" : "=m" (envp->__mxcsr));

	/* Clear exception flags in MXCSR */
	mxcsr = envp->__mxcsr;
	mxcsr &= ~FE_ALL_EXCEPT;

	/* Mask all exceptions */
	mxcsr \|= FE_ALL_EXCEPT << SSE_MASK_SHIFT;

	/* Store the MXCSR register */
	__asm__ __volatile__ ("ldmxcsr %0" : : "m" (mxcsr));

	return (0);
	}

	/*
	* The fesetenv() function attempts to establish the floating-point environment
	* represented by the object pointed to by envp. The argument `envp' points
	* to an object set by a call to fegetenv() or feholdexcept(), or equal a
	* floating-point environment macro. The fesetenv() function does not raise
	* floating-point exceptions, but only installs the state of the floating-point
	* status flags represented through its argument.
	*/
	int
	fesetenv(const fenv_t *envp)
	{
	/* Load the x87 floating-point environent */
	__asm__ __volatile__ ("fldenv %0" : : "m" (*envp));

	/* Store the MXCSR register */
	__asm__ __volatile__ ("ldmxcsr %0" : : "m" (envp->__mxcsr));

	return (0);
	}

	/*
	* The feupdateenv() function saves the currently raised floating-point
	* exceptions in its automatic storage, installs the floating-point environment
	* represented by the object pointed to by `envp', and then raises the saved
	* floating-point exceptions. The argument `envp' shall point to an object set
	* by a call to feholdexcept() or fegetenv(), or equal a floating-point
	* environment macro.
	*/
	int
	feupdateenv(const fenv_t *envp)
	{
	unsigned short status;
	unsigned int mxcsr;

	/* Store the x87 status register */
	__asm__ __volatile__ ("fnstsw %0" : "=am" (status));

	/* Store the MXCSR register */
	__asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));

	/* Install new floating-point environment */
	fesetenv(envp);

	/* Raise any previously accumulated exceptions */
	feraiseexcept(status \| mxcsr);

	return (0);
	}

	/*
	* The following functions are extentions to the standard
	*/
	int
	feenableexcept(int mask)
	{
	unsigned int mxcsr, omask;
	unsigned short control;

	mask &= FE_ALL_EXCEPT;

	__asm__ __volatile__ ("fnstcw %0" : "=m" (control));
	__asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));

	omask = ~(control \| (mxcsr >> SSE_MASK_SHIFT)) & FE_ALL_EXCEPT;
	control &= ~mask;
	__asm__ __volatile__ ("fldcw %0" : : "m" (control));

	mxcsr &= ~(mask << SSE_MASK_SHIFT);
	__asm__ __volatile__ ("ldmxcsr %0" : : "m" (mxcsr));

	return (omask);
	}

	int
	fedisableexcept(int mask)
	{
	unsigned int mxcsr, omask;
	unsigned short control;

	mask &= FE_ALL_EXCEPT;

	__asm__ __volatile__ ("fnstcw %0" : "=m" (control));
	__asm__ __volatile__ ("stmxcsr %0" : "=m" (mxcsr));

	omask = ~(control \| (mxcsr >> SSE_MASK_SHIFT)) & FE_ALL_EXCEPT;
	control \|= mask;
	__asm__ __volatile__ ("fldcw %0" : : "m" (control));

	mxcsr \|= mask << SSE_MASK_SHIFT;
	__asm__ __volatile__ ("ldmxcsr %0" : : "m" (mxcsr));

	return (omask);
	}

	int
	fegetexcept(void)
	{
	unsigned short control;

	/*
	* We assume that the masks for the x87 and the SSE unit are
	* the same.
	*/
	__asm__ __volatile__ ("fnstcw %0" : "=m" (control));

	return (~control & FE_ALL_EXCEPT);
	}