lib/ack/fphook/add_ext.fc

   1 /*
   2   (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
   3   See the copyright notice in the ACK home directory, in the file "Copyright".
   4 */
   5
   6 /* $Header$ */
   7
   8 /*
   9         ADD TWO EXTENDED FORMAT NUMBERS
  10 */
  11
  12 #include "FP_types.h"
  13
  14 void
  15 add_ext(e1,e2)
  16 register EXTEND *e1,*e2;
  17 {
  18         if ((e2->m1 | e2->m2) == 0L) {
  19                 return;
  20         }
  21         if ((e1->m1 | e1->m2) == 0L) {
  22                 *e1 = *e2;
  23                 return;
  24         }
  25         sft_ext(e1, e2);        /* adjust mantissas to equal powers */
  26         if (e1->sign != e2->sign) {
  27                 /* e1 + e2 = e1 - (-e2) */
  28                 if (e2->m1 > e1->m1 ||
  29                     (e2->m1 == e1->m1 && e2->m2 > e1->m2)) {
  30                         /*      abs(e2) > abs(e1) */
  31                         EXTEND x;
  32
  33                         x = *e1;
  34                         *e1 = *e2;
  35                         if (x.m2 > e1->m2) {
  36                                 e1->m1 -= 1;    /* carry in */
  37                         }
  38                         e1->m1 -= x.m1;
  39                         e1->m2 -= x.m2;
  40                 }
  41                 else {
  42                         if (e2->m2 > e1->m2)
  43                                 e1->m1 -= 1;    /* carry in */
  44                         e1->m1 -= e2->m1;
  45                         e1->m2 -= e2->m2;
  46                 }
  47         }
  48         else {
  49                 if (b64_add(&e1->mantissa,&e2->mantissa)) {     /* addition carry */
  50                         b64_rsft(&e1->mantissa);        /* shift mantissa one bit RIGHT */
  51                         e1->m1 |= 0x80000000L;  /* set max bit  */
  52                         e1->exp++;              /* increase the exponent */
  53                 }
  54         }
  55         nrm_ext(e1);
  56 }