156 lines
5.8 KiB
C
156 lines
5.8 KiB
C
#ifndef _ROUND_INTERNAL_H
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/*
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* round_internal.h
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*
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* $Id$
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*
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* Provides a generic implementation of the numerical rounding
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* algorithm, which is shared by all functions in the `round()',
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* `lround()' and `llround()' families.
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*
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* Written by Keith Marshall <keithmarshall@users.sourceforge.net>
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*
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* This is free software. You may redistribute and/or modify it as you
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* see fit, without restriction of copyright.
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*
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* This software is provided "as is", in the hope that it may be useful,
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* but WITHOUT WARRANTY OF ANY KIND, not even any implied warranty of
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* MERCHANTABILITY, nor of FITNESS FOR ANY PARTICULAR PURPOSE. At no
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* time will the author accept any form of liability for any damages,
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* however caused, resulting from the use of this software.
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*
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*/
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#define _ROUND_INTERNAL_H
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#include <math.h>
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#include <fenv.h>
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#define TYPE_PASTE( NAME, TYPE ) NAME##TYPE
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#define INPUT_TYPE INPUT_TYPEDEF( FUNCTION )
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#define INPUT_TYPEDEF( FUNCTION ) TYPE_PASTE( FUNCTION, _input_type )
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/*
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* The types for the formal parameter, to each of the derived functions.
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*/
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#define round_input_type double
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#define roundf_input_type float
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#define roundl_input_type long double
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#define lround_input_type double
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#define lroundf_input_type float
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#define lroundl_input_type long double
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#define llround_input_type double
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#define llroundf_input_type float
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#define llroundl_input_type long double
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#define RETURN_TYPE RETURN_TYPEDEF( FUNCTION )
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#define RETURN_TYPEDEF( FUNCTION ) TYPE_PASTE( FUNCTION, _return_type )
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/*
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* The types for the return value, from each of the derived functions.
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*/
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#define round_return_type double
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#define roundf_return_type float
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#define roundl_return_type long double
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#define lround_return_type long
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#define lroundf_return_type long
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#define lroundl_return_type long
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#define llround_return_type long long
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#define llroundf_return_type long long
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#define llroundl_return_type long long
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#define MAX_RETURN_VALUE RETURN_MAX( FUNCTION )
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#define RETURN_MAX( FUNCTION ) TYPE_PASTE( FUNCTION, _return_max )
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/*
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* The maximum values which may be returned by each of the derived functions
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* in the `lround' or the `llround' families.
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*/
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#define lround_return_max LONG_MAX
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#define lroundf_return_max LONG_MAX
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#define lroundl_return_max LONG_MAX
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#define llround_return_max LLONG_MAX
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#define llroundf_return_max LLONG_MAX
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#define llroundl_return_max LLONG_MAX
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#define MIN_RETURN_VALUE RETURN_MIN( FUNCTION )
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#define RETURN_MIN( FUNCTION ) TYPE_PASTE( FUNCTION, _return_min )
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/*
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* The minimum values which may be returned by each of the derived functions
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* in the `lround' or the `llround' families.
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*/
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#define lround_return_min LONG_MIN
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#define lroundf_return_min LONG_MIN
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#define lroundl_return_min LONG_MIN
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#define llround_return_min LLONG_MIN
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#define llroundf_return_min LLONG_MIN
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#define llroundl_return_min LLONG_MIN
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#define REF_VALUE( VALUE ) REF_TYPE( FUNCTION, VALUE )
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#define REF_TYPE( FUNC, VAL ) TYPE_PASTE( FUNC, _ref )( VAL )
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/*
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* Macros for expressing constant values of the appropriate data type,
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* for use in each of the derived functions.
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*/
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#define round_ref( VALUE ) VALUE
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#define lround_ref( VALUE ) VALUE
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#define llround_ref( VALUE ) VALUE
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#define roundl_ref( VALUE ) TYPE_PASTE( VALUE, L )
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#define lroundl_ref( VALUE ) TYPE_PASTE( VALUE, L )
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#define llroundl_ref( VALUE ) TYPE_PASTE( VALUE, L )
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#define roundf_ref( VALUE ) TYPE_PASTE( VALUE, F )
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#define lroundf_ref( VALUE ) TYPE_PASTE( VALUE, F )
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#define llroundf_ref( VALUE ) TYPE_PASTE( VALUE, F )
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static __inline__
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INPUT_TYPE __attribute__(( always_inline )) round_internal( INPUT_TYPE x )
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#define ROUND_MODES ( FE_TONEAREST | FE_UPWARD | FE_DOWNWARD | FE_TOWARDZERO )
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{
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/* Generic helper function, for rounding of the input parameter value to
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* the nearest integer value.
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*/
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INPUT_TYPE z;
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unsigned short saved_CW, tmp_required_CW;
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/* Rounding method suggested by Danny Smith <dannysmith@users.sf.net>
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*
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* Save the FPU control word state, set rounding mode TONEAREST, round the
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* input value, then restore the original FPU control word state.
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*/
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__asm__( "fnstcw %0;" : "=m"( saved_CW ));
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tmp_required_CW = ( saved_CW & ~ROUND_MODES ) | FE_TONEAREST;
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__asm__( "fldcw %0;" :: "m"( tmp_required_CW ));
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__asm__( "frndint;" : "=t"( z ) : "0"( x ));
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__asm__( "fldcw %0;" :: "m"( saved_CW ));
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/* We now have a possible rounded value; unfortunately the FPU uses the
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* `round-to-even' rule for exact mid-way cases, where both C99 and POSIX
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* require us to always round away from zero, so we need to adjust those
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* mid-way cases which the FPU rounded in the wrong direction.
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*
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* Correction method suggested by Greg Chicares <gchicares@sbcglobal.net>
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*/
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return x < REF_VALUE( 0.0 )
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? /*
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* For negative input values, an incorrectly rounded value will be
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* exactly 0.5 greater than the original value; when we find such an
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* exact rounding offset, we must subtract an additional 1.0 from the
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* rounded result, otherwise we return the rounded result unchanged.
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*/
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z - x == REF_VALUE( 0.5 ) ? z - REF_VALUE( 1.0 ) : z
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: /* For positive input values, an incorrectly rounded value will be
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* exactly 0.5 less than the original value; when we find such an exact
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* rounding offset, we must add an additional 1.0 to the rounded result,
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* otherwise we return the rounded result unchanged.
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*/
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x - z == REF_VALUE( 0.5 ) ? z + REF_VALUE( 1.0 ) : z;
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}
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#endif /* !defined _ROUND_INTERNAL_H: $RCSfile$: end of file */
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