/* $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>
/*
* The i387 defaults to Intel extended precision mode and round to nearest,
* with all exceptions masked.
*/
#define __INITIAL_NPXCW__ 0x037f
#define __INITIAL_MXCSR__ 0x1f80
#define __INITIAL_MXCSR_MASK__ 0xffbf
#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);
}