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+/* flonum_multip.c - multiply two flonums
+   Copyright (C) 1987, 1990, 1991 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.  */
+
+/* static const char rcsid[] = "$Id$"; */
+
+#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 (a, b, product)
+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
+	      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 */