/* $OpenBSD: dfsqrt.c,v 1.7 2003/04/10 17:27:58 mickey Exp $ */ /* (c) Copyright 1986 HEWLETT-PACKARD COMPANY To anyone who acknowledges that this file is provided "AS IS" without any express or implied warranty: permission to use, copy, modify, and distribute this file for any purpose is hereby granted without fee, provided that the above copyright notice and this notice appears in all copies, and that the name of Hewlett-Packard Company not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission. Hewlett-Packard Company makes no representations about the suitability of this software for any purpose. */ /* @(#)dfsqrt.c: Revision: 1.9.88.1 Date: 93/12/07 15:05:46 */ #include "float.h" #include "dbl_float.h" /* * Double Floating-point Square Root */ /*ARGSUSED*/ int dbl_fsqrt(srcptr, null, dstptr, status) dbl_floating_point *srcptr, *null, *dstptr; unsigned int *status; { register unsigned int srcp1, srcp2, resultp1, resultp2; register unsigned int newbitp1, newbitp2, sump1, sump2; register int src_exponent; register int guardbit = FALSE, even_exponent; Dbl_copyfromptr(srcptr,srcp1,srcp2); /* * check source operand for NaN or infinity */ if ((src_exponent = Dbl_exponent(srcp1)) == DBL_INFINITY_EXPONENT) { /* * is signaling NaN? */ if (Dbl_isone_signaling(srcp1)) { /* trap if INVALIDTRAP enabled */ if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION); /* make NaN quiet */ Set_invalidflag(); Dbl_set_quiet(srcp1); } /* * Return quiet NaN or positive infinity. * Fall thru to negative test if negative infinity. */ if (Dbl_iszero_sign(srcp1) || Dbl_isnotzero_mantissa(srcp1,srcp2)) { Dbl_copytoptr(srcp1,srcp2,dstptr); return(NOEXCEPTION); } } /* * check for zero source operand */ if (Dbl_iszero_exponentmantissa(srcp1,srcp2)) { Dbl_copytoptr(srcp1,srcp2,dstptr); return(NOEXCEPTION); } /* * check for negative source operand */ if (Dbl_isone_sign(srcp1)) { /* trap if INVALIDTRAP enabled */ if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION); /* make NaN quiet */ Set_invalidflag(); Dbl_makequietnan(srcp1,srcp2); Dbl_copytoptr(srcp1,srcp2,dstptr); return(NOEXCEPTION); } /* * Generate result */ if (src_exponent > 0) { even_exponent = Dbl_hidden(srcp1); Dbl_clear_signexponent_set_hidden(srcp1); } else { /* normalize operand */ Dbl_clear_signexponent(srcp1); src_exponent++; Dbl_normalize(srcp1,srcp2,src_exponent); even_exponent = src_exponent & 1; } if (even_exponent) { /* exponent is even */ /* Add comment here. Explain why odd exponent needs correction */ Dbl_leftshiftby1(srcp1,srcp2); } /* * Add comment here. Explain following algorithm. * * Trust me, it works. * */ Dbl_setzero(resultp1,resultp2); Dbl_allp1(newbitp1) = 1 << (DBL_P - 32); Dbl_setzero_mantissap2(newbitp2); while (Dbl_isnotzero(newbitp1,newbitp2) && Dbl_isnotzero(srcp1,srcp2)) { Dbl_addition(resultp1,resultp2,newbitp1,newbitp2,sump1,sump2); if(Dbl_isnotgreaterthan(sump1,sump2,srcp1,srcp2)) { Dbl_leftshiftby1(newbitp1,newbitp2); /* update result */ Dbl_addition(resultp1,resultp2,newbitp1,newbitp2, resultp1,resultp2); Dbl_subtract(srcp1,srcp2,sump1,sump2,srcp1,srcp2); Dbl_rightshiftby2(newbitp1,newbitp2); } else { Dbl_rightshiftby1(newbitp1,newbitp2); } Dbl_leftshiftby1(srcp1,srcp2); } /* correct exponent for pre-shift */ if (even_exponent) { Dbl_rightshiftby1(resultp1,resultp2); } /* check for inexact */ if (Dbl_isnotzero(srcp1,srcp2)) { if (!even_exponent & Dbl_islessthan(resultp1,resultp2,srcp1,srcp2)) { Dbl_increment(resultp1,resultp2); } guardbit = Dbl_lowmantissap2(resultp2); Dbl_rightshiftby1(resultp1,resultp2); /* now round result */ switch (Rounding_mode()) { case ROUNDPLUS: Dbl_increment(resultp1,resultp2); break; case ROUNDNEAREST: /* stickybit is always true, so guardbit * is enough to determine rounding */ if (guardbit) { Dbl_increment(resultp1,resultp2); } break; } /* increment result exponent by 1 if mantissa overflowed */ if (Dbl_isone_hiddenoverflow(resultp1)) src_exponent+=2; if (Is_inexacttrap_enabled()) { Dbl_set_exponent(resultp1, ((src_exponent-DBL_BIAS)>>1)+DBL_BIAS); Dbl_copytoptr(resultp1,resultp2,dstptr); return(INEXACTEXCEPTION); } else Set_inexactflag(); } else { Dbl_rightshiftby1(resultp1,resultp2); } Dbl_set_exponent(resultp1,((src_exponent-DBL_BIAS)>>1)+DBL_BIAS); Dbl_copytoptr(resultp1,resultp2,dstptr); return(NOEXCEPTION); }