lib/float/sub_ext.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 /* $Header$ */
   7
   8 /*
   9         SUBTRACT 2 EXTENDED FORMAT NUMBERS
  10 */
  11
  12 #include "FP_types.h"
  13
  14 void
  15 sub_ext(e1,e2)
  16 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                 e1->sign = e2->sign ? 0 : 1;
  24                 return;
  25         }
  26         sft_ext(e1, e2);
  27         if (e1->sign != e2->sign) {
  28                 /* e1 - e2 = e1 + (-e2) */
  29                 if (b64_add(&e1->mantissa,&e2->mantissa)) { /* addition carry */
  30                         b64_rsft(&e1->mantissa);      /* shift mantissa one bit RIGHT */
  31                         e1->m1 |= 0x80000000L;  /* set max bit  */
  32                         e1->exp++;              /* increase the exponent */
  33                 }
  34         }
  35         else if (e2->m1 > e1->m1 ||
  36                  (e2->m1 == e1->m1 && e2->m2 > e1->m2)) {
  37                 /*      abs(e2) > abs(e1) */
  38                 if (e1->m2 > e2->m2) {
  39                         e2->m1 -= 1;    /* carry in */
  40                 }
  41                 e2->m1 -= e1->m1;
  42                 e2->m2 -= e1->m2;
  43                 *e1 = *e2;
  44                 e1->sign = e2->sign ? 0 : 1;
  45         }
  46         else {
  47                 if (e2->m2 > e1->m2)
  48                         e1->m1 -= 1;    /* carry in */
  49                 e1->m1 -= e2->m1;
  50                 e1->m2 -= e2->m2;
  51         }
  52         nrm_ext(e1);
  53 }