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glibc  2.9
fenv.h
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00001 /* Copyright (C) 1997, 1998, 1999, 2000 Free Software Foundation, Inc.
00002    This file is part of the GNU C Library.
00003 
00004    The GNU C Library is free software; you can redistribute it and/or
00005    modify it under the terms of the GNU Lesser General Public
00006    License as published by the Free Software Foundation; either
00007    version 2.1 of the License, or (at your option) any later version.
00008 
00009    The GNU C Library is distributed in the hope that it will be useful,
00010    but WITHOUT ANY WARRANTY; without even the implied warranty of
00011    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00012    Lesser General Public License for more details.
00013 
00014    You should have received a copy of the GNU Lesser General Public
00015    License along with the GNU C Library; if not, write to the Free
00016    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00017    02111-1307 USA.  */
00018 
00019 #ifndef _FENV_H
00020 # error "Never use <bits/fenv.h> directly; include <fenv.h> instead."
00021 #endif
00022 
00023 
00024 /* Define the bits representing the exception.
00025 
00026    Note that these are the bit positions as defined by the OSF/1
00027    ieee_{get,set}_control_word interface and not by the hardware fpcr.
00028 
00029    See the Alpha Architecture Handbook section 4.7.7.3 for details,
00030    but in summary, trap shadows mean the hardware register can acquire
00031    extra exception bits so for proper IEEE support the tracking has to
00032    be done in software -- in this case with kernel support.
00033 
00034    As to why the system call interface isn't in the same format as
00035    the hardware register, only those crazy folks at DEC can tell you.  */
00036 
00037 enum
00038   {
00039 #ifdef __USE_GNU
00040     FE_DENORMAL =    1UL << 22,
00041 #define FE_DENORMAL  FE_DENORMAL
00042 #endif
00043 
00044     FE_INEXACT =     1UL << 21,
00045 #define FE_INEXACT   FE_INEXACT
00046 
00047     FE_UNDERFLOW =   1UL << 20,
00048 #define FE_UNDERFLOW FE_UNDERFLOW
00049 
00050     FE_OVERFLOW =    1UL << 19,
00051 #define FE_OVERFLOW  FE_OVERFLOW
00052 
00053     FE_DIVBYZERO =   1UL << 18,
00054 #define FE_DIVBYZERO FE_DIVBYZERO
00055 
00056     FE_INVALID =     1UL << 17,
00057 #define FE_INVALID   FE_INVALID
00058 
00059     FE_ALL_EXCEPT =  0x3f << 17
00060 #define FE_ALL_EXCEPT       FE_ALL_EXCEPT
00061   };
00062 
00063 /* Alpha chips support all four defined rouding modes.
00064 
00065    Note that code must be compiled to use dynamic rounding (/d) instructions
00066    to see these changes.  For gcc this is -mfp-rounding-mode=d; for DEC cc
00067    this is -fprm d.  The default for both is static rounding to nearest.
00068 
00069    These are shifted down 58 bits from the hardware fpcr because the
00070    functions are declared to take integers.  */
00071 
00072 enum
00073   {
00074     FE_TOWARDZERO =  0,
00075 #define FE_TOWARDZERO       FE_TOWARDZERO
00076 
00077     FE_DOWNWARD =    1,
00078 #define FE_DOWNWARD  FE_DOWNWARD
00079 
00080     FE_TONEAREST =   2,
00081 #define FE_TONEAREST FE_TONEAREST
00082 
00083     FE_UPWARD =             3,
00084 #define FE_UPWARD    FE_UPWARD
00085   };
00086 
00087 #ifdef __USE_GNU
00088 /* On later hardware, and later kernels for earlier hardware, we can forcibly
00089    underflow denormal inputs and outputs.  This can speed up certain programs
00090    significantly, usually without affecting accuracy.  */
00091 enum
00092   {
00093     FE_MAP_DMZ =     1UL << 12,    /* Map denorm inputs to zero */
00094 #define FE_MAP_DMZ   FE_MAP_DMZ
00095 
00096     FE_MAP_UMZ =     1UL << 13,    /* Map underflowed outputs to zero */
00097 #define FE_MAP_UMZ   FE_MAP_UMZ
00098   };
00099 #endif
00100 
00101 /* Type representing exception flags.  */
00102 typedef unsigned long int fexcept_t;
00103 
00104 /* Type representing floating-point environment.  */
00105 typedef unsigned long int fenv_t;
00106 
00107 /* If the default argument is used we use this value.  Note that due to
00108    architecture-specified page mappings, no user-space pointer will ever
00109    have its two high bits set.  Co-opt one.  */
00110 #define FE_DFL_ENV   ((__const fenv_t *) 0x8800000000000000UL)
00111 
00112 #ifdef __USE_GNU
00113 /* Floating-point environment where none of the exceptions are masked.  */
00114 # define FE_NOMASK_ENV      ((__const fenv_t *) 0x880000000000003eUL)
00115 
00116 /* Floating-point environment with (processor-dependent) non-IEEE floating
00117    point.  In this case, mapping denormals to zero.  */
00118 # define FE_NONIEEE_ENV ((__const fenv_t *) 0x8800000000003000UL)
00119 #endif
00120 
00121 /* The system calls to talk to the kernel's FP code.  */
00122 extern unsigned long int __ieee_get_fp_control (void) __THROW;
00123 extern void __ieee_set_fp_control (unsigned long int __value) __THROW;