sub.c

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/*
 * Copyright (c) 2005 Josef Cejka
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sftypes.h>
#include <sub.h>
#include <comparison.h>

float32 subFloat32(float32 a, float32 b)
{
        int expdiff;
        uint32_t exp1, exp2, frac1, frac2;
        float32 result;

        result.f = 0;
        
        expdiff = a.parts.exp - b.parts.exp;
        if ((expdiff < 0 ) || ((expdiff == 0) && (a.parts.fraction < b.parts.fraction))) {
                if (isFloat32NaN(b)) {
                        /* TODO: fix SigNaN */
                        if (isFloat32SigNaN(b)) {
                        };
                        return b;
                };
                
                if (b.parts.exp == FLOAT32_MAX_EXPONENT) { 
                        b.parts.sign = !b.parts.sign; /* num -(+-inf) = -+inf */
                        return b;
                }
                
                result.parts.sign = !a.parts.sign; 
                
                frac1 = b.parts.fraction;
                exp1 = b.parts.exp;
                frac2 = a.parts.fraction;
                exp2 = a.parts.exp;
                expdiff *= -1;
        } else {
                if (isFloat32NaN(a)) {
                        /* TODO: fix SigNaN */
                        if (isFloat32SigNaN(a) || isFloat32SigNaN(b)) {
                        };
                        return a;
                };
                
                if (a.parts.exp == FLOAT32_MAX_EXPONENT) { 
                        if (b.parts.exp == FLOAT32_MAX_EXPONENT) {
                                /* inf - inf => nan */
                                /* TODO: fix exception */
                                result.binary = FLOAT32_NAN;
                                return result;
                        };
                        return a;
                }
                
                result.parts.sign = a.parts.sign;
                
                frac1 = a.parts.fraction;
                exp1 = a.parts.exp;
                frac2 = b.parts.fraction;
                exp2 = b.parts.exp;     
        };
        
        if (exp1 == 0) {
                /* both are denormalized */
                result.parts.fraction = frac1-frac2;
                if (result.parts.fraction > frac1) {
                        /* TODO: underflow exception */
                        return result;
                };
                result.parts.exp = 0;
                return result;
        };

        /* add hidden bit */
        frac1 |= FLOAT32_HIDDEN_BIT_MASK; 
        
        if (exp2 == 0) {
                /* denormalized */
                --expdiff;      
        } else {
                /* normalized */
                frac2 |= FLOAT32_HIDDEN_BIT_MASK;
        };
        
        /* create some space for rounding */
        frac1 <<= 6;
        frac2 <<= 6;
        
        if (expdiff > FLOAT32_FRACTION_SIZE + 1) {
             goto done; 
             };
        
        frac1 = frac1 - (frac2 >> expdiff);
done:
        /* TODO: find first nonzero digit and shift result and detect possibly underflow */
        while ((exp1 > 0) && (!(frac1 & (FLOAT32_HIDDEN_BIT_MASK << 6 )))) {
                --exp1;
                frac1 <<= 1;
                        /* TODO: fix underflow - frac1 == 0 does not necessary means underflow... */
        };
        
        /* rounding - if first bit after fraction is set then round up */
        frac1 += 0x20;

        if (frac1 & (FLOAT32_HIDDEN_BIT_MASK << 7)) {
                ++exp1;
                frac1 >>= 1;
        };
        
        /*Clear hidden bit and shift */
        result.parts.fraction = ((frac1 >> 6) & (~FLOAT32_HIDDEN_BIT_MASK)); 
        result.parts.exp = exp1;
        
        return result;
}

float64 subFloat64(float64 a, float64 b)
{
        int expdiff;
        uint32_t exp1, exp2;
        uint64_t frac1, frac2;
        float64 result;

        result.d = 0;
        
        expdiff = a.parts.exp - b.parts.exp;
        if ((expdiff < 0 ) || ((expdiff == 0) && (a.parts.fraction < b.parts.fraction))) {
                if (isFloat64NaN(b)) {
                        /* TODO: fix SigNaN */
                        if (isFloat64SigNaN(b)) {
                        };
                        return b;
                };
                
                if (b.parts.exp == FLOAT64_MAX_EXPONENT) { 
                        b.parts.sign = !b.parts.sign; /* num -(+-inf) = -+inf */
                        return b;
                }
                
                result.parts.sign = !a.parts.sign; 
                
                frac1 = b.parts.fraction;
                exp1 = b.parts.exp;
                frac2 = a.parts.fraction;
                exp2 = a.parts.exp;
                expdiff *= -1;
        } else {
                if (isFloat64NaN(a)) {
                        /* TODO: fix SigNaN */
                        if (isFloat64SigNaN(a) || isFloat64SigNaN(b)) {
                        };
                        return a;
                };
                
                if (a.parts.exp == FLOAT64_MAX_EXPONENT) { 
                        if (b.parts.exp == FLOAT64_MAX_EXPONENT) {
                                /* inf - inf => nan */
                                /* TODO: fix exception */
                                result.binary = FLOAT64_NAN;
                                return result;
                        };
                        return a;
                }
                
                result.parts.sign = a.parts.sign;
                
                frac1 = a.parts.fraction;
                exp1 = a.parts.exp;
                frac2 = b.parts.fraction;
                exp2 = b.parts.exp;     
        };
        
        if (exp1 == 0) {
                /* both are denormalized */
                result.parts.fraction = frac1 - frac2;
                if (result.parts.fraction > frac1) {
                        /* TODO: underflow exception */
                        return result;
                };
                result.parts.exp = 0;
                return result;
        };

        /* add hidden bit */
        frac1 |= FLOAT64_HIDDEN_BIT_MASK; 
        
        if (exp2 == 0) {
                /* denormalized */
                --expdiff;      
        } else {
                /* normalized */
                frac2 |= FLOAT64_HIDDEN_BIT_MASK;
        };
        
        /* create some space for rounding */
        frac1 <<= 6;
        frac2 <<= 6;
        
        if (expdiff > FLOAT64_FRACTION_SIZE + 1) {
             goto done; 
             };
        
        frac1 = frac1 - (frac2 >> expdiff);
done:
        /* TODO: find first nonzero digit and shift result and detect possibly underflow */
        while ((exp1 > 0) && (!(frac1 & (FLOAT64_HIDDEN_BIT_MASK << 6 )))) {
                --exp1;
                frac1 <<= 1;
                        /* TODO: fix underflow - frac1 == 0 does not necessary means underflow... */
        };
        
        /* rounding - if first bit after fraction is set then round up */
        frac1 += 0x20;

        if (frac1 & (FLOAT64_HIDDEN_BIT_MASK << 7)) {
                ++exp1;
                frac1 >>= 1;
        };
        
        /*Clear hidden bit and shift */
        result.parts.fraction = ((frac1 >> 6) & (~FLOAT64_HIDDEN_BIT_MASK)); 
        result.parts.exp = exp1;
        
        return result;
}

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