source: mainline/softfloat/generic/common.c@ aa59fa0

/*
 * 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<common.h>

/* Table for fast leading zeroes counting */
char zeroTable[256] = {
        8, 7, 7, 6, 6, 6, 6, 4, 4, 4, 4, 4, 4, 4, 4, \
        3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, \
        2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, \
        2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, \
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, \
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};



/** Take fraction shifted by 10 bits to left, round it, normalize it and detect exceptions
 * @param exp exponent with bias
 * @param cfrac fraction shifted 10 places left with added hidden bit
 * @return valied float64
 */
float64 finishFloat64(int32_t cexp, uint64_t cfrac, char sign)
{
        float64 result;

        result.parts.sign = sign;

        /* find first nonzero digit and shift result and detect possibly underflow */
        while ((cexp > 0) && (cfrac) && (!(cfrac & (FLOAT64_HIDDEN_BIT_MASK << (64 - FLOAT64_FRACTION_SIZE - 1 ) )))) {
                cexp--; 
                cfrac <<= 1;
                        /* TODO: fix underflow */
        };
        
        if ((cexp < 0) || ( cexp == 0 && (!(cfrac & (FLOAT64_HIDDEN_BIT_MASK << (64 - FLOAT64_FRACTION_SIZE - 1)))))) {
                /* FIXME: underflow */
                result.parts.exp = 0;
                if ((cexp + FLOAT64_FRACTION_SIZE + 1) < 0) { /* +1 is place for rounding */
                        result.parts.fraction = 0;
                        return result;
                }
                
                while (cexp < 0) {
                        cexp++;
                        cfrac >>= 1;
                }
        
                cfrac += (0x1 << (64 - FLOAT64_FRACTION_SIZE - 3)); 
                
                if (!(cfrac & (FLOAT64_HIDDEN_BIT_MASK << (64 - FLOAT64_FRACTION_SIZE - 1)))) {
                        
                        result.parts.fraction = ((cfrac >>(64 - FLOAT64_FRACTION_SIZE - 2) ) & (~FLOAT64_HIDDEN_BIT_MASK)); 
                        return result;
                }       
        } else {
                cfrac += (0x1 << (64 - FLOAT64_FRACTION_SIZE - 3)); 
        }
        
        ++cexp;

        if (cfrac & (FLOAT64_HIDDEN_BIT_MASK << (64 - FLOAT64_FRACTION_SIZE - 1 ))) {
                ++cexp;
                cfrac >>= 1;
        }       

        /* check overflow */
        if (cexp >= FLOAT64_MAX_EXPONENT ) {
                /* FIXME: overflow, return infinity */
                result.parts.exp = FLOAT64_MAX_EXPONENT;
                result.parts.fraction = 0;
                return result;
        }

        result.parts.exp = (uint32_t)cexp;
        
        result.parts.fraction = ((cfrac >>(64 - FLOAT64_FRACTION_SIZE - 2 ) ) & (~FLOAT64_HIDDEN_BIT_MASK)); 
        
        return result;  
}

/** Counts leading zeroes in 64bit unsigned integer
 * @param i 
 */
int countZeroes64(uint64_t i)
{
        int j;
        for (j =0; j < 64; j += 8) {
                if ( i & (0xFFll << (56 - j))) {
                        return (j + countZeroes8(i >> (56 - j)));
                }
        }

        return 64;
}

/** Counts leading zeroes in 32bit unsigned integer
 * @param i 
 */
int countZeroes32(uint32_t i)
{
        int j;
        for (j =0; j < 32; j += 8) {
                if ( i & (0xFF << (24 - j))) {
                        return (j + countZeroes8(i >> (24 - j)));
                }
        }

        return 32;
}

/** Counts leading zeroes in byte
 * @param i 
 */
int countZeroes8(uint8_t i)
{
        return zeroTable[i];
}

/** Round and normalize number expressed by exponent and fraction with first bit (equal to hidden bit) at 30. bit
 * @param exp exponent 
 * @param fraction part with hidden bit shifted to 30. bit
 */
void roundFloat32(int32_t *exp, uint32_t *fraction)
{
        /* rounding - if first bit after fraction is set then round up */
        (*fraction) += (0x1 << 6);
        
        if ((*fraction) & (FLOAT32_HIDDEN_BIT_MASK << 8)) { 
                /* rounding overflow */
                ++(*exp);
                (*fraction) >>= 1;
        };
        
        if (((*exp) >= FLOAT32_MAX_EXPONENT ) || ((*exp) < 0)) {
                /* overflow - set infinity as result */
                (*exp) = FLOAT32_MAX_EXPONENT;
                (*fraction) = 0;
                return;
        }

        return;
}

/** Round and normalize number expressed by exponent and fraction with first bit (equal to hidden bit) at 62. bit
 * @param exp exponent 
 * @param fraction part with hidden bit shifted to 62. bit
 */
void roundFloat64(int32_t *exp, uint64_t *fraction)
{
        /* rounding - if first bit after fraction is set then round up */
        (*fraction) += (0x1 << 9);
        
        if ((*fraction) & (FLOAT64_HIDDEN_BIT_MASK << 11)) { 
                /* rounding overflow */
                ++(*exp);
                (*fraction) >>= 1;
        };
        
        if (((*exp) >= FLOAT64_MAX_EXPONENT ) || ((*exp) < 0)) {
                /* overflow - set infinity as result */
                (*exp) = FLOAT64_MAX_EXPONENT;
                (*fraction) = 0;
                return;
        }

        return;
}