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* The SB-Prolog System *
* Copyright SUNY at Stony Brook, 1986; University of Arizona, 1987 *
* *
************************************************************************/
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/* WAM representation of floats:
* bits 0-2 : tag (010);
* bits 3-7 : absolute value of exponent;
* bits 8-28: absolute value of mantissa;
* bit 29: sign of exponent (1: negative);
* bit 30: sign of mantissa (1: negative).
*/
#include "sim.h"
#include "aux.h"
#define Bit20 0x100000
#define Bits15to19 0x0f8000
#define MIN(x, y) (x > y ? y : x)
#define EXP_SIGN 0x20000000
#define MANT_SIGN 0x40000000
#define EXP_MAGN(op) (((unsigned)(op & 0xf8)) >> 3)
#define MANT_MAGN(op) (((unsigned)(op & 0x1fffff00)) >> 8)
double frexp(), ldexp(); /* C library routines */
/* "floatval" converts floats from the WAM representation to
* the machine representation.
*/
double floatval(op)
LONG op;
{
LONG exponent, exp;
double fval;
fval = (double)MANT_MAGN(op);
exponent = EXP_MAGN(op);
exp = (op & EXP_SIGN) ? -exponent : exponent;
if (op & MANT_SIGN)
fval = -fval;
fval = ldexp(fval, exp);
return fval;
}
/* "makefloat" converts floats from the machine representation
* to the WAM representation.
*/
LONG makefloat(op)
double op;
{
LONG exp_sign, mant_sign, int_op;
int exponent, nshift;
WORD num_gaps;
unsigned int mask;
if (op < 0) {
mant_sign = MANT_SIGN;
op = -op;
}
else mant_sign = 0;
op = frexp(op, &exponent);
if (op == 0.0 || exponent <= -32) {
int_op = 0;
exponent = 0;
} else {
while(!((int_op = (int)(op + 0.5)) & Bit20) && exponent > -31) {
/* keep top 10 bits clear for shifting */
mask = (int_op & Bits15to19) >> 15;
switch (mask) {
case 0: num_gaps = 6; break;
case 1: num_gaps = 5; break;
case 2:
case 3: num_gaps = 4; break;
case 4:
case 5:
case 6:
case 7: num_gaps = 3; break;
case 8:
case 9:
case 10:
case 11:
case 12:
case 13:
case 14:
case 15: num_gaps = 2; break;
default: /* cases 16 to 31 */
num_gaps = 1; break;
}
nshift = MIN(exponent - (-31), num_gaps);
switch (nshift) {
case 0 : break;
case 1 : op *= 2; break;
case 2 : op *= 4; break;
case 3 : op *= 8; break;
case 4 : op *= 16; break;
case 5 : op *= 32; break;
case 6 : op *= 64; break;
default: printf("makefloat: unexpected multiplier %d\n", nshift);
}
exponent -= nshift;
} /* while */
} /* else */
if (exponent < 0) {
exponent = -exponent;
exp_sign = EXP_SIGN;
} else exp_sign = 0;
return (((LONG)int_op << 8) | (exponent << 3) |
exp_sign | mant_sign | FLOAT_TAG);
}
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.