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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>

/** Subtract two float32 numbers with same signs

 */

float32 subFloat32(float32 a, float32 b)

{

    int expdiff;

    __u32 exp1, exp2, mant1, mant2;

    float32 result;

    result.f = 0;

    expdiff = a.parts.exp - b.parts.exp;

    if ((expdiff < 0 ) || ((expdiff == 0) && (a.parts.mantisa < b.parts.mantisa))) {

        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;

        mant1 = b.parts.mantisa;

        exp1 = b.parts.exp;

        mant2 = a.parts.mantisa;

        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;

        mant1 = a.parts.mantisa;

        exp1 = a.parts.exp;

        mant2 = b.parts.mantisa;

        exp2 = b.parts.exp;

    };

    if (exp1 == 0) {

        //both are denormalized

        result.parts.mantisa = mant1-mant2;

        if (result.parts.mantisa > mant1) {

            //TODO: underflow exception

            return result;

        };

        result.parts.exp = 0;

        return result;

    };

    /* add hidden bit */

    mant1 |= FLOAT32_HIDDEN_BIT_MASK;

    if (exp2 == 0) {

        /* denormalized */

        --expdiff; 

    } else {

        /* normalized */

        mant2 |= FLOAT32_HIDDEN_BIT_MASK;

    };

    /* create some space for rounding */

    mant1 <<= 6;

    mant2 <<= 6;

    if (expdiff > FLOAT32_MANTISA_SIZE + 1) {

         goto done;

         };

    mant1 = mant1 - (mant2 >> expdiff);

done:

    //TODO: find first nonzero digit and shift result and detect possibly underflow

    while ((exp1 > 0) && (!(mant1 & (FLOAT32_HIDDEN_BIT_MASK << 6 )))) {

        --exp1;

        mant1 <<= 1;

            /* TODO: fix underflow - mant1 == 0 does not necessary means underflow... */

    };

    /* rounding - if first bit after mantisa is set then round up */

    mant1 += 0x20;

    if (mant1 & (FLOAT32_HIDDEN_BIT_MASK << 7)) {

        ++exp1;

        mant1 >>= 1;

    };

    /*Clear hidden bit and shift */

    result.parts.mantisa = ((mant1 >> 6) & (~FLOAT32_HIDDEN_BIT_MASK));

    result.parts.exp = exp1;

    return result;

}

/** Subtract two float64 numbers with same signs

 */

float64 subFloat64(float64 a, float64 b)

{

    int expdiff;

    __u32 exp1, exp2;

    __u64 mant1, mant2;

    float64 result;

    result.d = 0;

    expdiff = a.parts.exp - b.parts.exp;

    if ((expdiff < 0 ) || ((expdiff == 0) && (a.parts.mantisa < b.parts.mantisa))) {

        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;

        mant1 = b.parts.mantisa;

        exp1 = b.parts.exp;

        mant2 = a.parts.mantisa;

        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;

        mant1 = a.parts.mantisa;

        exp1 = a.parts.exp;

        mant2 = b.parts.mantisa;

        exp2 = b.parts.exp;

    };

    if (exp1 == 0) {

        //both are denormalized

        result.parts.mantisa = mant1 - mant2;

        if (result.parts.mantisa > mant1) {

            //TODO: underflow exception

            return result;

        };

        result.parts.exp = 0;

        return result;

    };

    /* add hidden bit */

    mant1 |= FLOAT64_HIDDEN_BIT_MASK;

    if (exp2 == 0) {

        /* denormalized */

        --expdiff; 

    } else {

        /* normalized */

        mant2 |= FLOAT64_HIDDEN_BIT_MASK;

    };

    /* create some space for rounding */

    mant1 <<= 6;

    mant2 <<= 6;

    if (expdiff > FLOAT64_MANTISA_SIZE + 1) {

         goto done;

         };

    mant1 = mant1 - (mant2 >> expdiff);

done:

    //TODO: find first nonzero digit and shift result and detect possibly underflow

    while ((exp1 > 0) && (!(mant1 & (FLOAT64_HIDDEN_BIT_MASK << 6 )))) {

        --exp1;

        mant1 <<= 1;

            /* TODO: fix underflow - mant1 == 0 does not necessary means underflow... */

    };

    /* rounding - if first bit after mantisa is set then round up */

    mant1 += 0x20;

    if (mant1 & (FLOAT64_HIDDEN_BIT_MASK << 7)) {

        ++exp1;

        mant1 >>= 1;

    };

    /*Clear hidden bit and shift */

    result.parts.mantisa = ((mant1 >> 6) & (~FLOAT64_HIDDEN_BIT_MASK));

    result.parts.exp = exp1;

    return result;

}