4.3BSD - /usr/src/ucb/lisp/franz/68k/dsmult.c

   1: /* Copyright (c) 1982, Regents, University of California */
   2: /*
   3:  * $Header $
   4:  *
   5:  * dsmult(top,bot,mul) --
   6:  * multiply an array of longs on the stack, by mul.
   7:  * the element top through bot (inclusive) get changed.
   8:  * if you expect a carry out of the most significant,
   9:  * it is up to you to provide a space for it to overflow.
  10:  */
  11: 
  12: struct vl   { long high; long low; };
  13: dsmult(top,bot,mul)
  14: long *top, *bot, mul;
  15: {
  16:     register long *p;
  17:     struct vl work;
  18:     long add = 0;
  19: 
  20:     for(p = top; p >= bot; p--) {
  21:         emul(*p,mul,add,&work); /* *p has 30 bits of info, mul has 32
  22: 					   yielding a 62 bit product. */
  23:         *p = work.low & 0x3fffffff; /* the stack gets the low 30 bits */
  24:         add = work.high;        /* we want add to get the next 32 bits.
  25: 					   on a 68k you might better be able to
  26: 					   do this by shifts and tests on the
  27: 					   carry but I don't know how to do this
  28: 					   from C, and the code generated here
  29: 					   will not be much worse.  Far less
  30: 					   bad than shifting work.low to the
  31: 					   right 30 bits just to get the top 2.
  32: 					   */
  33:         add <<= 2;
  34:         if(work.low < 0) add += 2;
  35:         if(work.low & 0x40000000) add += 1;
  36:     }
  37:     p[1] = work.low;  /* on the final store want all 32 bits. */
  38: }

Defined functions

Defined struct's