// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Linux/PA-RISC Project (http://www.parisc-linux.org/)
 *
 * Floating-point emulation code
 *  Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org>
 */
/*
 * BEGIN_DESC
 *
 *  File:
 *      @(#)    pa/spmath/sfsqrt.c              $Revision: 1.1 $
 *
 *  Purpose:
 *      Single Floating-point Square Root
 *
 *  External Interfaces:
 *      sgl_fsqrt(srcptr,_nullptr,dstptr,status)
 *
 *  Internal Interfaces:
 *
 *  Theory:
 *      <<please update with a overview of the operation of this file>>
 *
 * END_DESC
*/


#include "float.h"
#include "sgl_float.h"

/*
 *  Single Floating-point Square Root
 */

/*ARGSUSED*/
unsigned int
sgl_fsqrt(
    sgl_floating_point *srcptr,
    unsigned int *_nullptr,
    sgl_floating_point *dstptr,
    unsigned int *status)
{
        register unsigned int src, result;
        register int src_exponent;
        register unsigned int newbit, sum;
        register boolean guardbit = FALSE, even_exponent;

        src = *srcptr;
        /*
         * check source operand for NaN or infinity
         */
        if ((src_exponent = Sgl_exponent(src)) == SGL_INFINITY_EXPONENT) {
                /*
                 * is signaling NaN?
                 */
                if (Sgl_isone_signaling(src)) {
                        /* trap if INVALIDTRAP enabled */
                        if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
                        /* make NaN quiet */
                        Set_invalidflag();
                        Sgl_set_quiet(src);
                }
                /*
                 * Return quiet NaN or positive infinity.
                 *  Fall through to negative test if negative infinity.
                 */
                if (Sgl_iszero_sign(src) || Sgl_isnotzero_mantissa(src)) {
                        *dstptr = src;
                        return(NOEXCEPTION);
                }
        }

        /*
         * check for zero source operand
         */
        if (Sgl_iszero_exponentmantissa(src)) {
                *dstptr = src;
                return(NOEXCEPTION);
        }

        /*
         * check for negative source operand 
         */
        if (Sgl_isone_sign(src)) {
                /* trap if INVALIDTRAP enabled */
                if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
                /* make NaN quiet */
                Set_invalidflag();
                Sgl_makequietnan(src);
                *dstptr = src;
                return(NOEXCEPTION);
        }

        /*
         * Generate result
         */
        if (src_exponent > 0) {
                even_exponent = Sgl_hidden(src);
                Sgl_clear_signexponent_set_hidden(src);
        }
        else {
                /* normalize operand */
                Sgl_clear_signexponent(src);
                src_exponent++;
                Sgl_normalize(src,src_exponent);
                even_exponent = src_exponent & 1;
        }
        if (even_exponent) {
                /* exponent is even */
                /* Add comment here.  Explain why odd exponent needs correction */
                Sgl_leftshiftby1(src);
        }
        /*
         * Add comment here.  Explain following algorithm.
         * 
         * Trust me, it works.
         *
         */
        Sgl_setzero(result);
        newbit = 1 << SGL_P;
        while (newbit && Sgl_isnotzero(src)) {
                Sgl_addition(result,newbit,sum);
                if(sum <= Sgl_all(src)) {
                        /* update result */
                        Sgl_addition(result,(newbit<<1),result);
                        Sgl_subtract(src,sum,src);
                }
                Sgl_rightshiftby1(newbit);
                Sgl_leftshiftby1(src);
        }
        /* correct exponent for pre-shift */
        if (even_exponent) {
                Sgl_rightshiftby1(result);
        }

        /* check for inexact */
        if (Sgl_isnotzero(src)) {
                if (!even_exponent && Sgl_islessthan(result,src)) 
                        Sgl_increment(result);
                guardbit = Sgl_lowmantissa(result);
                Sgl_rightshiftby1(result);

                /*  now round result  */
                switch (Rounding_mode()) {
                case ROUNDPLUS:
                     Sgl_increment(result);
                     break;
                case ROUNDNEAREST:
                     /* stickybit is always true, so guardbit 
                      * is enough to determine rounding */
                     if (guardbit) {
                        Sgl_increment(result);
                     }
                     break;
                }
                /* increment result exponent by 1 if mantissa overflowed */
                if (Sgl_isone_hiddenoverflow(result)) src_exponent+=2;

                if (Is_inexacttrap_enabled()) {
                        Sgl_set_exponent(result,
                         ((src_exponent-SGL_BIAS)>>1)+SGL_BIAS);
                        *dstptr = result;
                        return(INEXACTEXCEPTION);
                }
                else Set_inexactflag();
        }
        else {
                Sgl_rightshiftby1(result);
        }
        Sgl_set_exponent(result,((src_exponent-SGL_BIAS)>>1)+SGL_BIAS);
        *dstptr = result;
        return(NOEXCEPTION);
}