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    Length: 5526 (0x1596)
    Types: TextFile
    Names: »missing.c«

└─⟦a0efdde77⟧ Bits:30001252 EUUGD11 Tape, 1987 Spring Conference Helsinki
    └─⟦this⟧ »EUUGD11/gnu-31mar87/scheme/microcode/missing.c« 

TextFile

/* -*-C-*- is a horrible language, and Emacs agrees. */

/****************************************************************
*                                                               *
*                         Copyright (c) 1986                    *
*               Massachusetts Institute of Technology           *
*                                                               *
* This material was developed by the Scheme project at the      *
* Massachusetts Institute of Technology, Department of          *
* Electrical Engineering and Computer Science.  Permission to   *
* copy this software, to redistribute it, and to use it for any *
* purpose is granted, subject to the following restrictions and *
* understandings.                                               *
*                                                               *
* 1. Any copy made of this software must include this copyright *
* notice in full.                                               *
*                                                               *
* 2. Users of this software agree to make their best efforts (a)*
* to return to the MIT Scheme project any improvements or       *
* extensions that they make, so that these may be included in   *
* future releases; and (b) to inform MIT of noteworthy uses of  *
* this software.                                                *
*                                                               *
* 3.  All materials developed as a consequence of the use of    *
* this software shall duly acknowledge such use, in accordance  *
* with the usual standards of acknowledging credit in academic  *
* research.                                                     *
*                                                               *
* 4. MIT has made no warrantee or representation that the       *
* operation of this software will be error-free, and MIT is     *
* under no obligation to provide any services, by way of        *
* maintenance, update, or otherwise.                            *
*                                                               *
* 5.  In conjunction with products arising from the use of this *
* material, there shall be no use of the name of the            *
* Massachusetts Institute of Technology nor of any adaptation   *
* thereof in any advertising, promotional, or sales literature  *
* without prior written consent from MIT in each case.          *
*                                                               *
****************************************************************/
\f


/* File: MISSING.C
 * This file contains utilities potentially missing from the math library
 */

#include "config.h"
#define boolean int
#define false 0
#define true 1

extern double frexp(), ldexp();

static boolean floating_table_initialized = false;
static double floating_table[(2*FLONUM_EXPT_SIZE)-1];
static int exponent_table[(2*FLONUM_EXPT_SIZE)-1];

initialize_floating_table()
{ register int index, exponent;
  register int *int_table = &exponent_table[FLONUM_EXPT_SIZE-1];
  register double *the_table = &floating_table[FLONUM_EXPT_SIZE-1];
  register double x;
  the_table[0] = 1.0;
  int_table[0] = 0;
  for (x = 2.0, index = 1, exponent = 1;
       index < FLONUM_EXPT_SIZE;
       x *= x, index += 1, exponent += exponent)
  { the_table[index] = x;
    int_table[index] = exponent;
  }
  for (x = 0.5, index = -1, exponent = -1;
       index > -FLONUM_EXPT_SIZE;
       x *= x, index -= 1, exponent += exponent)
  { the_table[index] = x;
    int_table[index] = exponent;
  }
  floating_table_initialized = true;
}

double frexp(value, eptr)
double value;
int *eptr;
{ register double mant;
  register int exponent, index;
  register double *the_table = &floating_table[FLONUM_EXPT_SIZE-1];
  register int *int_table = &exponent_table[FLONUM_EXPT_SIZE-1];

  if (value == 0.0)
  { *eptr = 0;
    return 0.0;
  }
  if (!floating_table_initialized) initialize_floating_table();
  mant = ((value < 0.0) ? -value : value);
  exponent = 0;
  while (mant < 0.5)
  { for (index = -FLONUM_EXPT_SIZE+1;
	 the_table[index] < mant;
	 index += 1) ;
    exponent += int_table[index];
    mant /= the_table[index];
  }
  if (mant >= 1.0)
  { while (mant >= 2.0)
    { for (index = FLONUM_EXPT_SIZE-1;
	   the_table[index] > mant;
	   index -= 1) ;
      exponent += int_table[index];
      mant /= the_table[index];
    }
    mant /= 2.0;
    exponent += 1;
  }
  *eptr = exponent;
  return ((value < 0.0) ? -mant : mant);
}

double ldexp(value, exponent)
register double value;
register int exponent;
{ register int index;
  register double *the_table = &floating_table[FLONUM_EXPT_SIZE-1];
  register int *int_table = &exponent_table[FLONUM_EXPT_SIZE-1];

  if (value == 0.0) return 0.0;
  if (!floating_table_initialized) initialize_floating_table();
  while (exponent > 0)
  { for(index = FLONUM_EXPT_SIZE-1;
	int_table[index] > exponent;
	index -= 1) ;
    exponent -= int_table[index];
    value *= the_table[index];
  }
  while (exponent < 0)
  { for(index = -FLONUM_EXPT_SIZE+1;
	int_table[index] < exponent;
	index += 1) ;
    exponent -= int_table[index];
    value *= the_table[index];
  }
  return value;
}

\f


#if DEBUG

#include <stdio.h>

main()
{ double input, output;
  int exponent;

  while (true)
  { printf("Number -> ");
    scanf("%F", &input);
    output = frexp(input, &exponent);
    printf("Input = %G; Output = %G; Exponent = %d\n",
	   input, output, exponent);
    printf("Result = %G\n", ldexp(output, exponent));
  }
}
#endif