glibc/sysdeps/arm/fpu/fpu_control.h

/* FPU control word definitions.  ARM version.
   Copyright (C) 1996, 1997, 1998 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#ifndef _FPU_CONTROL_H
#define _FPU_CONTROL_H

/* We have a slight terminology confusion here.  On the ARM, the register
 * we're interested in is actually the FPU status word - the FPU control
 * word is something different (which is implementation-defined and only
 * accessible from supervisor mode.)  
 *
 * The FPSR looks like this:
 *
 *     31-24        23-16          15-8              7-0
 * | system ID | trap enable | system control | exception flags | 
 *
 * We ignore the system ID bits; for interest's sake they are:
 *
 *  0000	"old" FPE
 *  1000	FPPC hardware
 *  0001	FPE 400
 *  1001	FPA hardware
 *
 * The trap enable and exception flags are both structured like this:
 *
 *     7 - 5     4     3     2     1     0
 * | reserved | INX | UFL | OFL | DVZ | IVO | 
 *
 * where a `1' bit in the enable byte means that the trap can occur, and
 * a `1' bit in the flags byte means the exception has occurred.
 *
 * The exceptions are:
 *
 *  IVO - invalid operation
 *  DVZ - divide by zero
 *  OFL - overflow
 *  UFL - underflow
 *  INX - inexact (do not use; implementations differ)
 *
 * The system control byte looks like this:
 *
 *     7-5      4    3    2    1    0
 * | reserved | AC | EP | SO | NE | ND |
 * 
 * where the bits mean
 *
 *  ND - no denormalised numbers (force them all to zero)
 *  NE - enable NaN exceptions
 *  SO - synchronous operation
 *  EP - use expanded packed-decimal format
 *  AC - use alternate definition for C flag on compare operations
 */

#define _FPU_RESERVED 0xfff0e0f0  /* These bits are reserved.  */

/* The fdlibm code requires no interrupts for exceptions.  Don't
   change the rounding mode, it would break long double I/O!  */
#define _FPU_DEFAULT  0x00000000 /* Default value.  */

/* Type of the control word.  */
typedef unsigned int fpu_control_t;

/* Macros for accessing the hardware control word.  */
#define _FPU_GETCW(cw) __asm__ ("rfs %0" : "=r" (cw))
#define _FPU_SETCW(cw) __asm__ ("wfs %0" : : "r" (cw))

/* Default control word set at startup.  */
extern fpu_control_t __fpu_control;

#endif /* _FPU_CONTROL_H */