source: mainline/uspace/lib/softfloat/sub.c@ c300bb5

/*
 * Copyright (c) 2005 Josef Cejka
 * Copyright (c) 2011 Petr Koupy
 * 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.
 */

/** @addtogroup softfloat
 * @{
 */
/** @file Substraction functions.
 */

#include "sub.h"
#include "comparison.h"
#include "common.h"
#include "add.h"

/** Subtract two single-precision floats with the same sign.
 *
 * @param a First input operand.
 * @param b Second input operand.
 *
 * @return Result of substraction.
 *
 */
float32 sub_float32(float32 a, float32 b)
{
        int expdiff;
        uint32_t exp1, exp2, frac1, frac2;
        float32 result;

        result.bin = 0;

        expdiff = a.parts.exp - b.parts.exp;
        if ((expdiff < 0) || ((expdiff == 0) &&
            (a.parts.fraction < b.parts.fraction))) {
                if (is_float32_nan(b)) {
                        if (is_float32_signan(b)) {
                                // TODO: fix SigNaN
                        }

                        return b;
                }

                if (b.parts.exp == FLOAT32_MAX_EXPONENT) {
                        /* num -(+-inf) = -+inf */
                        b.parts.sign = !b.parts.sign;
                        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 (is_float32_nan(a)) {
                        if ((is_float32_signan(a)) || (is_float32_signan(b))) {
                                // TODO: fix SigNaN
                        }

                        return a;
                }

                if (a.parts.exp == FLOAT32_MAX_EXPONENT) {
                        if (b.parts.exp == FLOAT32_MAX_EXPONENT) {
                                /* inf - inf => nan */
                                // TODO: fix exception
                                result.bin = 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;
}

/** Subtract two double-precision floats with the same sign.
 *
 * @param a First input operand.
 * @param b Second input operand.
 *
 * @return Result of substraction.
 *
 */
float64 sub_float64(float64 a, float64 b)
{
        int expdiff;
        uint32_t exp1, exp2;
        uint64_t frac1, frac2;
        float64 result;

        result.bin = 0;

        expdiff = a.parts.exp - b.parts.exp;
        if ((expdiff < 0) ||
            ((expdiff == 0) && (a.parts.fraction < b.parts.fraction))) {
                if (is_float64_nan(b)) {
                        if (is_float64_signan(b)) {
                                // TODO: fix SigNaN
                        }

                        return b;
                }

                if (b.parts.exp == FLOAT64_MAX_EXPONENT) {
                        /* num -(+-inf) = -+inf */
                        b.parts.sign = !b.parts.sign;
                        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 (is_float64_nan(a)) {
                        if (is_float64_signan(a) || is_float64_signan(b)) {
                                // TODO: fix SigNaN
                        }

                        return a;
                }

                if (a.parts.exp == FLOAT64_MAX_EXPONENT) {
                        if (b.parts.exp == FLOAT64_MAX_EXPONENT) {
                                /* inf - inf => nan */
                                // TODO: fix exception
                                result.bin = 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;
}

/** Subtract two quadruple-precision floats with the same sign.
 *
 * @param a First input operand.
 * @param b Second input operand.
 *
 * @return Result of substraction.
 *
 */
float128 sub_float128(float128 a, float128 b)
{
        int expdiff;
        uint32_t exp1, exp2;
        uint64_t frac1_hi, frac1_lo, frac2_hi, frac2_lo, tmp_hi, tmp_lo;
        float128 result;

        result.bin.hi = 0;
        result.bin.lo = 0;

        expdiff = a.parts.exp - b.parts.exp;
        if ((expdiff < 0) || ((expdiff == 0) &&
            lt128(a.parts.frac_hi, a.parts.frac_lo, b.parts.frac_hi, b.parts.frac_lo))) {
                if (is_float128_nan(b)) {
                        if (is_float128_signan(b)) {
                                // TODO: fix SigNaN
                        }

                        return b;
                }

                if (b.parts.exp == FLOAT128_MAX_EXPONENT) {
                        /* num -(+-inf) = -+inf */
                        b.parts.sign = !b.parts.sign;
                        return b;
                }

                result.parts.sign = !a.parts.sign;

                frac1_hi = b.parts.frac_hi;
                frac1_lo = b.parts.frac_lo;
                exp1 = b.parts.exp;
                frac2_hi = a.parts.frac_hi;
                frac2_lo = a.parts.frac_lo;
                exp2 = a.parts.exp;
                expdiff *= -1;
        } else {
                if (is_float128_nan(a)) {
                        if (is_float128_signan(a) || is_float128_signan(b)) {
                                // TODO: fix SigNaN
                        }

                        return a;
                }

                if (a.parts.exp == FLOAT128_MAX_EXPONENT) {
                        if (b.parts.exp == FLOAT128_MAX_EXPONENT) {
                                /* inf - inf => nan */
                                // TODO: fix exception
                                result.bin.hi = FLOAT128_NAN_HI;
                                result.bin.lo = FLOAT128_NAN_LO;
                                return result;
                        }
                        return a;
                }

                result.parts.sign = a.parts.sign;

                frac1_hi = a.parts.frac_hi;
                frac1_lo = a.parts.frac_lo;
                exp1 = a.parts.exp;
                frac2_hi = b.parts.frac_hi;
                frac2_lo = b.parts.frac_lo;
                exp2 = b.parts.exp;
        }

        if (exp1 == 0) {
                /* both are denormalized */
                sub128(frac1_hi, frac1_lo, frac2_hi, frac2_lo, &tmp_hi, &tmp_lo);
                result.parts.frac_hi = tmp_hi;
                result.parts.frac_lo = tmp_lo;
                if (lt128(frac1_hi, frac1_lo, result.parts.frac_hi, result.parts.frac_lo)) {
                        // TODO: underflow exception
                        return result;
                }

                result.parts.exp = 0;
                return result;
        }

        /* add hidden bit */
        or128(frac1_hi, frac1_lo,
            FLOAT128_HIDDEN_BIT_MASK_HI, FLOAT128_HIDDEN_BIT_MASK_LO,
            &frac1_hi, &frac1_lo);

        if (exp2 == 0) {
                /* denormalized */
                --expdiff;
        } else {
                /* normalized */
                or128(frac2_hi, frac2_lo,
                    FLOAT128_HIDDEN_BIT_MASK_HI, FLOAT128_HIDDEN_BIT_MASK_LO,
                    &frac2_hi, &frac2_lo);
        }

        /* create some space for rounding */
        lshift128(frac1_hi, frac1_lo, 6, &frac1_hi, &frac1_lo);
        lshift128(frac2_hi, frac2_lo, 6, &frac2_hi, &frac2_lo);

        if (expdiff > FLOAT128_FRACTION_SIZE + 1)
                goto done;

        rshift128(frac2_hi, frac2_lo, expdiff, &tmp_hi, &tmp_lo);
        sub128(frac1_hi, frac1_lo, tmp_hi, tmp_lo, &frac1_hi, &frac1_lo);

done:
        /* TODO: find first nonzero digit and shift result and detect possibly underflow */
        lshift128(FLOAT128_HIDDEN_BIT_MASK_HI, FLOAT128_HIDDEN_BIT_MASK_LO, 6,
            &tmp_hi, &tmp_lo);
        and128(frac1_hi, frac1_lo, tmp_hi, tmp_lo, &tmp_hi, &tmp_lo);
        while ((exp1 > 0) && (!lt128(0x0ll, 0x0ll, tmp_hi, tmp_lo))) {
                --exp1;
                lshift128(frac1_hi, frac1_lo, 1, &frac1_hi, &frac1_lo);
                /* TODO: fix underflow - frac1 == 0 does not necessary means underflow... */

                lshift128(FLOAT128_HIDDEN_BIT_MASK_HI, FLOAT128_HIDDEN_BIT_MASK_LO, 6,
                    &tmp_hi, &tmp_lo);
                and128(frac1_hi, frac1_lo, tmp_hi, tmp_lo, &tmp_hi, &tmp_lo);
        }

        /* rounding - if first bit after fraction is set then round up */
        add128(frac1_hi, frac1_lo, 0x0ll, 0x20ll, &frac1_hi, &frac1_lo);

        lshift128(FLOAT128_HIDDEN_BIT_MASK_HI, FLOAT128_HIDDEN_BIT_MASK_LO, 7,
            &tmp_hi, &tmp_lo);
        and128(frac1_hi, frac1_lo, tmp_hi, tmp_lo, &tmp_hi, &tmp_lo);
        if (lt128(0x0ll, 0x0ll, tmp_hi, tmp_lo)) {
                ++exp1;
                rshift128(frac1_hi, frac1_lo, 1, &frac1_hi, &frac1_lo);
        }

        /* Clear hidden bit and shift */
        rshift128(frac1_hi, frac1_lo, 6, &frac1_hi, &frac1_lo);
        not128(FLOAT128_HIDDEN_BIT_MASK_HI, FLOAT128_HIDDEN_BIT_MASK_LO,
            &tmp_hi, &tmp_lo);
        and128(frac1_hi, frac1_lo, tmp_hi, tmp_lo, &tmp_hi, &tmp_lo);
        result.parts.frac_hi = tmp_hi;
        result.parts.frac_lo = tmp_lo;

        result.parts.exp = exp1;

        return result;
}

#ifdef float32_t

float32_t __subsf3(float32_t a, float32_t b)
{
        float32_u ua;
        ua.val = a;

        float32_u ub;
        ub.val = b;

        float32_u res;

        if (ua.data.parts.sign != ub.data.parts.sign) {
                ub.data.parts.sign = !ub.data.parts.sign;
                res.data = add_float32(ua.data, ub.data);
        } else
                res.data = sub_float32(ua.data, ub.data);

        return res.val;
}

float32_t __aeabi_fsub(float32_t a, float32_t b)
{
        float32_u ua;
        ua.val = a;

        float32_u ub;
        ub.val = b;

        float32_u res;

        if (ua.data.parts.sign != ub.data.parts.sign) {
                ub.data.parts.sign = !ub.data.parts.sign;
                res.data = add_float32(ua.data, ub.data);
        } else
                res.data = sub_float32(ua.data, ub.data);

        return res.val;
}

#endif

#ifdef float64_t

float64_t __subdf3(float64_t a, float64_t b)
{
        float64_u ua;
        ua.val = a;

        float64_u ub;
        ub.val = b;

        float64_u res;

        if (ua.data.parts.sign != ub.data.parts.sign) {
                ub.data.parts.sign = !ub.data.parts.sign;
                res.data = add_float64(ua.data, ub.data);
        } else
                res.data = sub_float64(ua.data, ub.data);

        return res.val;
}

float64_t __aeabi_dsub(float64_t a, float64_t b)
{
        float64_u ua;
        ua.val = a;

        float64_u ub;
        ub.val = b;

        float64_u res;

        if (ua.data.parts.sign != ub.data.parts.sign) {
                ub.data.parts.sign = !ub.data.parts.sign;
                res.data = add_float64(ua.data, ub.data);
        } else
                res.data = sub_float64(ua.data, ub.data);

        return res.val;
}

#endif

#ifdef float128_t

float128_t __subtf3(float128_t a, float128_t b)
{
        float128_u ua;
        ua.val = a;

        float128_u ub;
        ub.val = b;

        float128_u res;

        if (ua.data.parts.sign != ub.data.parts.sign) {
                ub.data.parts.sign = !ub.data.parts.sign;
                res.data = add_float128(ua.data, ub.data);
        } else
                res.data = sub_float128(ua.data, ub.data);

        return res.val;
}

void _Qp_sub(float128_t *c, float128_t *a, float128_t *b)
{
        *c = __subtf3(*a, *b);
}

#endif

/** @}
 */