131 lines
2.6 KiB
C
131 lines
2.6 KiB
C
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/***
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*util.c - utilities for fp transcendentals
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*
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* Copyright (c) 1991-2001, Microsoft Corporation. All rights reserved.
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*
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*Purpose:
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* _set_exp and _add_exp are as those defined in Cody & Waite
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*
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*Revision History:
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* 08-15-91 GDP written
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* 10-20-91 GDP removed _rint, unsafe_intrnd
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* 02-05-92 GDP added _fpclass
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* 03-27-92 GDP added _d_min
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* 06-23-92 GDP added _d_mzero
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*
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*******************************************************************************/
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#include "trans.h"
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/* define special values */
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_dbl _d_inf = {SET_DBL (0x7ff00000, 0x0) }; //positive infinity
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_dbl _d_ind = {SET_DBL (D_IND_HI, D_IND_LO)}; //real indefinite
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_dbl _d_max = {SET_DBL (0x7fefffff, 0xffffffff)}; //max double
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_dbl _d_min = {SET_DBL (0x00100000, 0x00000000)}; //min normalized double
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_dbl _d_mzero = {SET_DBL (0x80000000, 0x00000000)}; //negative zero
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double _set_exp(double x, int exp)
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/* does not check validity of exp */
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{
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double retval;
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int biased_exp;
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retval = x;
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biased_exp = exp + D_BIASM1;
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*D_EXP(retval) = (unsigned short) (*D_EXP(x) & 0x800f | (biased_exp << 4));
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return retval;
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}
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int _get_exp(double x)
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{
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signed short exp;
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exp = (signed short)((*D_EXP(x) & 0x7ff0) >> 4);
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exp -= D_BIASM1; //unbias
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return (int) exp;
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}
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double _add_exp(double x, int exp)
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{
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return _set_exp(x, INTEXP(x)+exp);
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}
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double _set_bexp(double x, int bexp)
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/* does not check validity of bexp */
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{
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double retval;
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retval = x;
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*D_EXP(retval) = (unsigned short) (*D_EXP(x) & 0x800f | (bexp << 4));
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return retval;
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}
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int _sptype(double x)
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{
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if (IS_D_INF(x))
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return T_PINF;
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if (IS_D_MINF(x))
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return T_NINF;
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if (IS_D_QNAN(x))
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return T_QNAN;
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if (IS_D_SNAN(x))
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return T_SNAN;
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return 0;
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}
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/***
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*double _decomp(double x, double *expptr)
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*
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*Purpose:
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* decompose a number to a normalized mantisa and exponent
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*
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*Entry:
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*
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*Exit:
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*
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*Exceptions:
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*
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*******************************************************************************/
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double _decomp(double x, int *pexp)
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{
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int exp;
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double man;
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if (x == 0) {
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man = 0;
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exp = 0;
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}
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else if (IS_D_DENORM(x)) {
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int neg;
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exp = 1-D_BIASM1;
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neg = x < 0.0;
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while((*D_EXP(x) & 0x0010) == 0) {
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/* shift mantissa to the left until bit 52 is 1 */
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(*D_HI(x)) <<= 1;
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if (*D_LO(x) & 0x80000000)
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(*D_HI(x)) |= 0x1;
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(*D_LO(x)) <<= 1;
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exp--;
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}
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(*D_EXP(x)) &= 0xffef; /* clear bit 52 */
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if (neg) {
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(*D_EXP(x)) |= 0x8000; /* set sign bit */
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}
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man = _set_exp(x,0);
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}
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else {
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man = _set_exp(x,0);
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exp = INTEXP(x);
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}
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*pexp = exp;
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return man;
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}
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