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    Length: 3812 (0xee4)
    Types: TextFile
    Names: »mul.c«

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

TextFile

/*	Emacs -*-C-*-an't tell the language			*/

/****************************************************************
*                                                               *
*                         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: MUL.C
 *
 * This file contains the portable fixnum multiplication procedure.
 * Returns NIL if the result does not fit in a fixnum.
 * Note: This has only been tried on machines with long = 32 bits.
 * This file is included in the appropriate os file if needed.
 */

#define HALF_WORD_SIZE	((sizeof(long)*CHAR_SIZE)/2)
#define HALF_WORD_MASK	(1<<HALF_WORD_SIZE)-1
#define MAX_MIDDLE	(1<<((ADDRESS_LENGTH-1)-HALF_WORD_SIZE))
#define MAX_FIXNUM	(1<<ADDRESS_LENGTH)
#define	ABS(x)		(((x) < 0) ? -(x) : (x))

Pointer Mul(Arg1, Arg2)
long Arg1, Arg2;
{ long A, B, C;
  fast long Hi_A, Hi_B, Lo_A, Lo_B, Lo_C, Middle_C;
  Boolean Sign;
  Sign_Extend(Arg1, A); Sign_Extend(Arg2, B);
  Sign = ((A < 0) == (B < 0));
  A = ABS(A); B = ABS(B);
  Hi_A = (A >> HALF_WORD_SIZE) & HALF_WORD_MASK;
  Hi_B = (B >> HALF_WORD_SIZE) & HALF_WORD_MASK;
  Lo_A = A & HALF_WORD_MASK;  Lo_B = B & HALF_WORD_MASK;
  Lo_C = Lo_A * Lo_B;
  if (Lo_C > FIXNUM_SIGN_BIT) return NIL;
  Middle_C = Lo_A * Hi_B + Hi_A * Lo_B;
  if (Middle_C >= MAX_MIDDLE) return NIL;
  if ((Hi_A * Hi_B) > 0) return NIL;
  C = Lo_C + (Middle_C << HALF_WORD_SIZE);
  if (Fixnum_Fits(C))
  { if (Sign || (C == 0)) return FIXNUM_0 + C;
    else return FIXNUM_0 + (MAX_FIXNUM - C);
  }
  return NIL;
}