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gml_Fraction.h Go to the documentation of this file. /** @file gml_Fraction.h * * Extraction of the IEEE floating-point representation to do integer math. * * Copyright (c) 2003-2004 CLIPS-IMAG * * See the file "gml_LicenseTerms.txt" for information on usage and redistribution * of this file, and for a DISCLAIMER OF ALL WARRANTIES. * * Created on April, 2003 (JL). * Ported to GML on January 19, 2004 (JL). */ #ifndef __GML_FRACTION__ #define __GML_FRACTION__ #include <assert.h> #include <math.h> #include "gml/base/gml_Types.h" #include "gml/base/gml_Errors.h" #include "gml/math/gml_Math.h" /// /// gml_TFloatUnion -- /// A structure to extract the fields of an /// IEEE 32-bit floating point number. /// union gml_TFloatUnion { Float32 fFloat; ///< full floating-point representation struct { #if BYTE_ORDER == BIG_ENDIAN unsigned int fSign : 1; ///< sign bit unsigned int fExponent : 8; ///< 8-bit binary exponent unsigned int fRemainder : 23; ///< 23-bit binary mantissa #else unsigned int fRemainder : 23; ///< 23-bit binary mantissa unsigned int fExponent : 8; ///< 8-bit binary exponent unsigned int fSign : 1; ///< sign bit #endif }; }; /// /// gml_TFraction -- /// Fast integer representation of a floating-point number between 0 and 1. /// Provides a Merge() method for fast blending of two integers /// (e.g. for alpha-compositing purposes) /// class gml_TFraction { public: /// /// Constructor -- /// Build a gml_TFraction from the IEEE 32-bit float <fraction>. /// gml_TFraction (Float32 fraction) { const gml_TFloatUnion fu = { fraction }; assert (fraction >= 0.0F && fraction <= 1.0F); fExponent = 127 - fu.fExponent + 23; fNumerator1 = fu.fRemainder + (1 << 23); fNumerator2 = (1 << fExponent) - fNumerator1; } /// /// Constructor -- /// Build a gml_TFraction as <numerator> / 2 ** <exponent>. /// gml_TFraction (UInt32 numerator, UInt8 exponent) { assert (numerator < (1 << 23)); assert (exponent < (1 << 7)); fExponent = exponent; fNumerator1 = numerator; fNumerator2 = (1 << fExponent) - fNumerator1; } /// /// Constructor -- /// Build the fraction representing 1. /// gml_TFraction () { fExponent = 0; fNumerator1 = 1; fNumerator2 = 0; } /// /// Merge -- /// Return a*f + b*(1-f) using only integer arithmetics. /// inline UInt32 Merge (const UInt32 a, const UInt32 b) const { return (UInt64(a) * fNumerator1 + UInt64(b) * fNumerator2) >> fExponent; } /// /// Numerator -- /// Return the numerator. /// inline UInt32 Numerator () const { return fNumerator1; } /// /// Exponent -- /// Return the exponent. /// inline UInt8 Exponent () const { return fExponent; } /// /// Value -- /// Return the floating-point value corresponding to this fraction /// inline Float32 Value () const { return Divide (Float32(fNumerator1), Float32(1UL << fExponent)); } protected: UInt8 fExponent; ///< the opposite of the fraction's power-of-two exponent UInt32 fNumerator1; ///< the fraction's numerator UInt32 fNumerator2; ///< the numerator of the fraction's complement to 1 } ; /// /// Merge -- /// Return the <alpha>-compositon of <a> and <b>. /// inline UInt32 Merge (UInt32 a, UInt32 b, UInt8 alpha) { #ifdef __GML_AVOID_EUCLIDIAN_DIVISION // avoid doing a division using 255 ~= 2^16 / 257 return ((a * (255 - alpha) + b * alpha) * 257UL) >> 16; #else return (a * (255 - alpha) + b * alpha) / 255; #endif } #endif /* __GML_FRACTION__ */ Generated on Tue Jun 12 14:03:27 2007 for gml by Doxygen 1.5.2.

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