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+/* flonum_mult.c - multiply two flonums
+ Copyright 1987, 1990, 1991, 1992, 1995, 2000, 2002, 2003, 2007
+ Free Software Foundation, Inc.
+
+ This file is part of GAS, the GNU Assembler.
+
+ GAS is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3, or (at your option)
+ any later version.
+
+ GAS is distributed in the hope that it will be useful, but WITHOUT
+ ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
+ License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with GAS; see the file COPYING. If not, write to the Free
+ Software Foundation, 51 Franklin Street - Fifth Floor, Boston, MA
+ 02110-1301, USA. */
+
+#include "ansidecl.h"
+#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 ...) */
+
+void
+flonum_multip (const FLONUM_TYPE *a, const FLONUM_TYPE *b,
+ FLONUM_TYPE *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 work;
+ unsigned long carry;
+ long exponent;
+ LITTLENUM_TYPE *q;
+ long 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
+ /* Watch out for sign extension! Without the casts, on
+ the DEC Alpha, the multiplication result is *signed*
+ int, which gets sign-extended to convert to the
+ unsigned long! */
+ work += (unsigned long) a->low[A] * (unsigned long) 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;
+}