+/* flonum_multip.c - multiply two flonums
+ Copyright (C) 1987 Free Software Foundation, Inc.
+
+This file is part of Gas, the GNU Assembler.
+
+The GNU assembler is distributed in the hope that it will be
+useful, but WITHOUT ANY WARRANTY. No author or distributor
+accepts responsibility to anyone for the consequences of using it
+or for whether it serves any particular purpose or works at all,
+unless he says so in writing. Refer to the GNU Assembler General
+Public License for full details.
+
+Everyone is granted permission to copy, modify and redistribute
+the GNU Assembler, but only under the conditions described in the
+GNU Assembler General Public License. A copy of this license is
+supposed to have been given to you along with the GNU Assembler
+so you can know your rights and responsibilities. It should be
+in a file named COPYING. Among other things, the copyright
+notice and this notice must be preserved on all copies. */
+
+#include "flonum.h"
+
+/* plan for a . b => p(roduct)
+
+
+ +-------+-------+-/ /-+-------+-------+
+ | a | a | ... | a | a |
+ | A | A-1 | | 1 | 0 |
+ +-------+-------+-/ /-+-------+-------+
+
+
+ +-------+-------+-/ /-+-------+-------+
+ | b | b | ... | b | b |
+ | B | B-1 | | 1 | 0 |
+ +-------+-------+-/ /-+-------+-------+
+
+
+ +-------+-------+-/ /-+-------+-/ /-+-------+-------+
+ | p | p | ... | p | ... | p | p |
+ | A+B+1| A+B | | N | | 1 | 0 |
+ +-------+-------+-/ /-+-------+-/ /-+-------+-------+
+
+ /^\
+ (carry) a .b ... | ... a .b a .b
+ A B | 0 1 0 0
+ |
+ ... | ... a .b
+ | 1 0
+ |
+ | ...
+ |
+ |
+ |
+ | ___
+ | \
+ +----- P = > a .b
+ N /__ i j
+
+ N = 0 ... A+B
+
+ for all i,j where i+j=N
+ [i,j integers > 0]
+
+a[], b[], p[] may not intersect.
+Zero length factors signify 0 significant bits: treat as 0.0.
+0.0 factors do the right thing.
+Zero length product OK.
+
+I chose the ForTran accent "foo[bar]" instead of the C accent "*garply"
+because I felt the ForTran way was more intuitive. The C way would
+probably yield better code on most C compilers. Dean Elsner.
+(C style also gives deeper insight [to me] ... oh well ...)
+*/
+\f
+void
+flonum_multip (a, b, product)
+ FLONUM_TYPE * a,
+ * b,
+ * product;
+{
+ int size_of_a; /* 0 origin */
+ int size_of_b; /* 0 origin */
+ int size_of_product; /* 0 origin */
+ int size_of_sum; /* 0 origin */
+ int extra_product_positions;/* 1 origin */
+ unsigned long int work;
+ unsigned long int carry;
+ long int exponent;
+ LITTLENUM_TYPE * q;
+ long int significant; /* TRUE when we emit a non-0 littlenum */
+ /* ForTran accent follows. */
+ int P; /* Scan product low-order -> high. */
+ int N; /* As in sum above. */
+ int A; /* Which [] of a? */
+ int B; /* Which [] of b? */
+
+ if((a->sign!='-' && a->sign!='+') || (b->sign!='-' && b->sign!='+')) {
+ /* ...
+ Got to fail somehow. Any suggestions? */
+ product->sign=0;
+ return;
+ }
+ product -> sign = (a->sign == b->sign) ? '+' : '-';
+ size_of_a = a -> leader - a -> low;
+ size_of_b = b -> leader - b -> low;
+ exponent = a -> exponent + b -> exponent;
+ size_of_product = product -> high - product -> low;
+ size_of_sum = size_of_a + size_of_b;
+ extra_product_positions = size_of_product - size_of_sum;
+ if (extra_product_positions < 0)
+ {
+ P = extra_product_positions; /* P < 0 */
+ exponent -= extra_product_positions; /* Increases exponent. */
+ }
+ else
+ {
+ P = 0;
+ }
+ carry = 0;
+ significant = 0;
+ for (N = 0;
+ N <= size_of_sum;
+ N++)
+ {
+ work = carry;
+ carry = 0;
+ for (A = 0;
+ A <= N;
+ A ++)
+ {
+ B = N - A;
+ if (A <= size_of_a && B <= size_of_b && B >= 0)
+ {
+#ifdef TRACE
+printf("a:low[%d.]=%04x b:low[%d.]=%04x work_before=%08x\n", A, a->low[A], B, b->low[B], work);
+#endif
+ work += a -> low [A] * b -> low [B];
+ carry += work >> LITTLENUM_NUMBER_OF_BITS;
+ work &= LITTLENUM_MASK;
+#ifdef TRACE
+printf("work=%08x carry=%04x\n", work, carry);
+#endif
+ }
+ }
+ significant |= work;
+ if (significant || P<0)
+ {
+ if (P >= 0)
+ {
+ product -> low [P] = work;
+#ifdef TRACE
+printf("P=%d. work[p]:=%04x\n", P, work);
+#endif
+ }
+ P ++;
+ }
+ else
+ {
+ extra_product_positions ++;
+ exponent ++;
+ }
+ }
+ /*
+ * [P]-> position # size_of_sum + 1.
+ * This is where 'carry' should go.
+ */
+#ifdef TRACE
+printf("final carry =%04x\n", carry);
+#endif
+ if (carry)
+ {
+ if (extra_product_positions > 0)
+ {
+ product -> low [P] = carry;
+ }
+ else
+ {
+ /* No room at high order for carry littlenum. */
+ /* Shift right 1 to make room for most significant littlenum. */
+ exponent ++;
+ P --;
+ for (q = product -> low + P;
+ q >= product -> low;
+ q --)
+ {
+ work = * q;
+ * q = carry;
+ carry = work;
+ }
+ }
+ }
+ else
+ {
+ P --;
+ }
+ product -> leader = product -> low + P;
+ product -> exponent = exponent;
+}
+
+/* end: flonum_multip.c */
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