Trailing-Edge
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PDP-10 Archives
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SRI_NIC_PERM_FS_1_19910112
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kccdist/lib/pml/dxexp.c
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/*
* +++ NAME +++
*
* DXEXP extract double precision numbers exponent
*
* +++ INDEX +++
*
* DXEXP
* math libraries
* machine dependent routines
*
* +++ DESCRIPTION +++
*
* Extracts exponent from a double precision number and
* returns it as a normal length integer.
*
* +++ USAGE +++
*
* int dxexp(value)
* double value;
*
* +++ PROGRAMMER +++
*
* Fred Fish
* Goodyear Aerospace Corp, Arizona Div.
* (602) 932-7000 work
* (602) 894-6881 home
*
* +++ INTERNALS +++
*
* This routine is highly machine dependent. As such, no
* attempt was made to make it general, hence it may have
* to be completely rewritten when transportation of the
* floating point library is attempted.
*
* For the DECSYSTEM-20 the double precision word format is:
*
* WORD N => SEEEEEEEEMMMMMMMMMMMMMMMMMMMMMMMMMMM
* WORD N+1 => XMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
*
* For the PDP-11 the double precision word format is:
*
* WORD N => SEEEEEEEEMMMMMMM
* WORD N+1 => MMMMMMMMMMMMMMMM
* WORD N+2 => MMMMMMMMMMMMMMMM
* WORD N+3 => MMMMMMMMMMMMMMMM
*
* Where: S => Sign bit
* E => Exponent
* X => Ignored (set to 0)
* M => Mantissa bit
*
*
*/
/*)LIBRARY
*/
#include <stdio.h>
#include "c:pmluse.h"
#include "pml.h"
#ifdef PDP10
#define EXP_MASK 0377000000000 /* Mask for exponent */
#define EXP_SHIFTS 27 /* Shifts to get into LSB's */
#endif
#ifdef pdp11
#define EXP_MASK 077600 /* Mask for exponent */
#define EXP_SHIFTS 7 /* Shifts to get into LSB's */
#endif
#ifdef vax
#define EXP_MASK 077600 /* Mask for exponent */
#define EXP_SHIFTS 7 /* Shifts to get into LSB's */
#endif
int dxexp(value)
double value;
{
register int *vpntr;
if (value == 0.0) {
return (0);
} else {
vpntr = &value;
#ifdef PDP10
if (value < 0.0) { /* Exponent is complemented */
*vpntr = ~*vpntr;
}
#endif
*vpntr &= EXP_MASK;
*vpntr = *vpntr >> EXP_SHIFTS;
return (*vpntr - 128);
}
}