84 lines
2.8 KiB
C
84 lines
2.8 KiB
C
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/**
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* PANDA 3D SOFTWARE
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* Copyright (c) Carnegie Mellon University. All rights reserved.
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*
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* All use of this software is subject to the terms of the revised BSD
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* license. You should have received a copy of this license along
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* with this source code in a file named "LICENSE."
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*
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* @file nearly_zero.h
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* @author drose
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* @date 2000-03-08
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*/
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#ifndef NEARLY_ZERO_H
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#define NEARLY_ZERO_H
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#include "dtoolbase.h"
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// The following two functions are defined just to make the NEARLY_ZERO()
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// macro work. They each return a suitable nearly-zero value for their
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// corresponding numeric type.
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// Note that declaring these small numeric values first as a static const
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// identifier, and then returning the value of that identifier, seems to lead
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// to compilation errors (at least in VC7) in which sometimes
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// IS_THRESHOLD_COMPEQ(a, a, get_nearly_zero_value(a)) != 0.
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constexpr double
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get_nearly_zero_value(double) {
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return 1.0e-12;
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}
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constexpr float
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get_nearly_zero_value(float) {
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return 1.0e-6f;
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}
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constexpr int
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get_nearly_zero_value(int) {
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// This is a bit silly, but we should nevertheless define it in case it is
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// called for an integer type.
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return 0;
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}
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// IS_THRESHOLD_ZERO(value, threshold) returns true if the value is within
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// threshold of zero.
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#define IS_THRESHOLD_ZERO(value, threshold) \
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((value) < (threshold) && (value) > -(threshold))
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// IS_THRESHOLD_EQUAL(value1, value2, threshold) returns true if the two
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// values are within threshold of each other.
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#define IS_THRESHOLD_EQUAL(value1, value2, threshold) \
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(IS_THRESHOLD_ZERO((value1) - (value2), threshold))
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// IS_THRESHOLD_COMPEQ(value1, value2, threshold) returns true if the two
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// values are equal within threshold tolerance. Unlike IS_THRESHOLD_EQUAL,
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// the transitive principle is guaranteed: IS_THRESHOLD_COMPEQ(a, b, t) &&
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// IS_THRESHOLD_COMPEQ(b, c, t) implies IS_THRESHOLD_COMPEQ(a, c, t).
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#define IS_THRESHOLD_COMPEQ(value1, value2, threshold) \
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(cfloor(value1 / threshold + 0.5f) == cfloor(value2 / threshold + 0.5f))
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// NEARLY_ZERO(float) returns a number that is considered to be so close to
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// zero as not to matter for a float. NEARLY_ZERO(double) returns a similar,
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// smaller number for a double.
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#define NEARLY_ZERO(FLOATTYPE) (get_nearly_zero_value((FLOATTYPE)0))
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// IS_NEARLY_ZERO(value) returns true if the value is very close to zero.
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#define IS_NEARLY_ZERO(value) \
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(IS_THRESHOLD_ZERO(value, get_nearly_zero_value(value)))
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// IS_NEARLY_EQUAL(value1, value2) returns true if the two values are very
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// close to each other.
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#define IS_NEARLY_EQUAL(value1, value2) \
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(IS_THRESHOLD_EQUAL(value1, value2, get_nearly_zero_value(value1)))
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// MAYBE_ZERO(value) returns 0 if the value is nearly zero, and the value
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// itself otherwise.
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#define MAYBE_ZERO(value) \
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(IS_NEARLY_ZERO(value) ? 0 : (value))
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#endif
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