175 строки
4.1 KiB
C
175 строки
4.1 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Linux/PA-RISC Project (http://www.parisc-linux.org/)
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*
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* Floating-point emulation code
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* Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org>
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*/
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/*
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* BEGIN_DESC
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*
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* File:
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* @(#) pa/spmath/sfsqrt.c $Revision: 1.1 $
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*
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* Purpose:
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* Single Floating-point Square Root
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*
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* External Interfaces:
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* sgl_fsqrt(srcptr,nullptr,dstptr,status)
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*
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* Internal Interfaces:
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*
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* Theory:
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* <<please update with a overview of the operation of this file>>
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*
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* END_DESC
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*/
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#include "float.h"
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#include "sgl_float.h"
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/*
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* Single Floating-point Square Root
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*/
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/*ARGSUSED*/
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unsigned int
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sgl_fsqrt(
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sgl_floating_point *srcptr,
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unsigned int *nullptr,
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sgl_floating_point *dstptr,
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unsigned int *status)
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{
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register unsigned int src, result;
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register int src_exponent;
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register unsigned int newbit, sum;
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register boolean guardbit = FALSE, even_exponent;
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src = *srcptr;
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/*
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* check source operand for NaN or infinity
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*/
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if ((src_exponent = Sgl_exponent(src)) == SGL_INFINITY_EXPONENT) {
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/*
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* is signaling NaN?
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*/
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if (Sgl_isone_signaling(src)) {
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/* trap if INVALIDTRAP enabled */
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if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
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/* make NaN quiet */
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Set_invalidflag();
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Sgl_set_quiet(src);
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}
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/*
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* Return quiet NaN or positive infinity.
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* Fall through to negative test if negative infinity.
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*/
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if (Sgl_iszero_sign(src) || Sgl_isnotzero_mantissa(src)) {
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*dstptr = src;
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return(NOEXCEPTION);
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}
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}
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/*
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* check for zero source operand
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*/
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if (Sgl_iszero_exponentmantissa(src)) {
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*dstptr = src;
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return(NOEXCEPTION);
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}
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/*
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* check for negative source operand
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*/
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if (Sgl_isone_sign(src)) {
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/* trap if INVALIDTRAP enabled */
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if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
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/* make NaN quiet */
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Set_invalidflag();
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Sgl_makequietnan(src);
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*dstptr = src;
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return(NOEXCEPTION);
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}
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/*
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* Generate result
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*/
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if (src_exponent > 0) {
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even_exponent = Sgl_hidden(src);
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Sgl_clear_signexponent_set_hidden(src);
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}
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else {
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/* normalize operand */
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Sgl_clear_signexponent(src);
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src_exponent++;
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Sgl_normalize(src,src_exponent);
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even_exponent = src_exponent & 1;
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}
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if (even_exponent) {
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/* exponent is even */
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/* Add comment here. Explain why odd exponent needs correction */
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Sgl_leftshiftby1(src);
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}
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/*
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* Add comment here. Explain following algorithm.
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*
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* Trust me, it works.
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*
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*/
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Sgl_setzero(result);
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newbit = 1 << SGL_P;
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while (newbit && Sgl_isnotzero(src)) {
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Sgl_addition(result,newbit,sum);
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if(sum <= Sgl_all(src)) {
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/* update result */
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Sgl_addition(result,(newbit<<1),result);
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Sgl_subtract(src,sum,src);
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}
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Sgl_rightshiftby1(newbit);
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Sgl_leftshiftby1(src);
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}
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/* correct exponent for pre-shift */
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if (even_exponent) {
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Sgl_rightshiftby1(result);
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}
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/* check for inexact */
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if (Sgl_isnotzero(src)) {
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if (!even_exponent && Sgl_islessthan(result,src))
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Sgl_increment(result);
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guardbit = Sgl_lowmantissa(result);
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Sgl_rightshiftby1(result);
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/* now round result */
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switch (Rounding_mode()) {
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case ROUNDPLUS:
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Sgl_increment(result);
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break;
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case ROUNDNEAREST:
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/* stickybit is always true, so guardbit
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* is enough to determine rounding */
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if (guardbit) {
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Sgl_increment(result);
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}
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break;
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}
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/* increment result exponent by 1 if mantissa overflowed */
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if (Sgl_isone_hiddenoverflow(result)) src_exponent+=2;
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if (Is_inexacttrap_enabled()) {
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Sgl_set_exponent(result,
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((src_exponent-SGL_BIAS)>>1)+SGL_BIAS);
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*dstptr = result;
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return(INEXACTEXCEPTION);
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}
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else Set_inexactflag();
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}
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else {
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Sgl_rightshiftby1(result);
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}
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Sgl_set_exponent(result,((src_exponent-SGL_BIAS)>>1)+SGL_BIAS);
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*dstptr = result;
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return(NOEXCEPTION);
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}
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