modules/src/flt_arith/flt_add.c

   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 /* $Id: flt_add.c,v 1.7 1994/06/24 11:15:33 ceriel Exp $ */
   7
   8 #include "flt_misc.h"
   9
  10 void
  11 flt_add(e1,e2,e3)
  12         register flt_arith *e1,*e2,*e3;
  13 {
  14         /*      Add two extended numbers e1 and e2, and put the result
  15                 in e3
  16         */
  17         flt_arith ce1, ce2;
  18         int diff;
  19
  20         flt_status = 0;
  21         if ((e2->m1 | e2->m2) == 0L) {
  22                 *e3 = *e1;
  23                 return;
  24         }
  25         if ((e1->m1 | e1->m2) == 0L) {
  26                 *e3 = *e2;
  27                 return;
  28         }
  29         ce2 = *e2;
  30         ce1 = *e1;
  31         e1 = &ce1;
  32         e2 = &ce2;
  33
  34         /* adjust mantissas to equal power */
  35         diff = e2->flt_exp - e1->flt_exp;
  36         if (diff < 0) {
  37                 diff = -diff;
  38                 e2->flt_exp += diff;
  39                 flt_b64_sft(&(e2->flt_mantissa), diff);
  40         }
  41         else if (diff > 0) {
  42                 e1->flt_exp += diff;
  43                 flt_b64_sft(&(e1->flt_mantissa), diff);
  44         }
  45         if (e1->flt_sign != e2->flt_sign) {
  46                 /* e2 + e1 = e2 - (-e1) */
  47                 int tmp = ucmp(e1->m1, e2->m1);
  48                 int tmp2 = ucmp(e1->m2, e2->m2);
  49                 if (tmp > 0 || (tmp == 0 && tmp2 > 0)) {
  50                         /*      abs(e1) > abs(e2) */
  51                         if (tmp2 < 0) {
  52                                 e1->m1 -= 1;    /* carry in */
  53                         }
  54                         e1->m1 -= e2->m1;
  55                         e1->m2 -= e2->m2;
  56                         *e3 = *e1;
  57                 }
  58                 else {
  59                         if (tmp2 > 0)
  60                                 e2->m1 -= 1;    /* carry in */
  61                         e2->m1 -= e1->m1;
  62                         e2->m2 -= e1->m2;
  63                         *e3 = *e2;
  64                 }
  65         }
  66         else {
  67                 *e3 = *e2;
  68                 if (flt_b64_add(&e3->flt_mantissa,&e1->flt_mantissa)) {/* addition carry */
  69                         flt_b64_sft(&e3->flt_mantissa, 1);
  70                         e3->m1 |= 0x80000000L;  /* set max bit  */
  71                         e3->flt_exp++;          /* increase the exponent */
  72                 }
  73         }
  74         flt_nrm(e3);
  75         flt_chk(e3);
  76 }
  77
  78 void
  79 flt_sub(e1,e2,e3)
  80         flt_arith *e1,*e2,*e3;
  81 {
  82         e2->flt_sign = ! e2->flt_sign;
  83         flt_add(e1,e2,e3);
  84         e2->flt_sign = ! e2->flt_sign;
  85 }