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[/] [openrisc/] [trunk/] [gnu-old/] [binutils-2.18.50/] [gas/] [flonum-mult.c] - Blame information for rev 816

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/* flonum_mult.c - multiply two flonums
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   Copyright 1987, 1990, 1991, 1992, 1995, 2000, 2002, 2003, 2007
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   Free Software Foundation, Inc.
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   This file is part of GAS, the GNU Assembler.
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   GAS is free software; you can redistribute it and/or modify
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   it under the terms of the GNU General Public License as published by
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   the Free Software Foundation; either version 3, or (at your option)
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   any later version.
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   GAS is distributed in the hope that it will be useful, but WITHOUT
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   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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   or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
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   License for more details.
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   You should have received a copy of the GNU General Public License
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   along with GAS; see the file COPYING.  If not, write to the Free
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   Software Foundation, 51 Franklin Street - Fifth Floor, Boston, MA
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   02110-1301, USA.  */
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#include "ansidecl.h"
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#include "flonum.h"
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/*      plan for a . b => p(roduct)
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        +-------+-------+-/   /-+-------+-------+
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        | a     | a     |  ...  | a     | a     |
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        |  A    |  A-1  |       |  1    |  0    |
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        +-------+-------+-/   /-+-------+-------+
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        +-------+-------+-/   /-+-------+-------+
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        | b     | b     |  ...  | b     | b     |
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        |  B    |  B-1  |       |  1    |  0    |
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        +-------+-------+-/   /-+-------+-------+
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        +-------+-------+-/   /-+-------+-/   /-+-------+-------+
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        | p     | p     |  ...  | p     |  ...  | p     | p     |
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        |  A+B+1|  A+B  |       |  N    |       |  1    |  0    |
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        +-------+-------+-/   /-+-------+-/   /-+-------+-------+
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        /^\
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        (carry) a .b       ...      |      ...   a .b    a .b
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        A  B                |             0  1    0  0
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        |
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        ...         |      ...   a .b
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        |                 1  0
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        |
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        |          ...
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        |
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        |
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        |
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        |                 ___
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        |                 \
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        +-----  P  =   >  a .b
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        N         /__  i  j
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        N = 0 ... A+B
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        for all i,j where i+j=N
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        [i,j integers > 0]
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        a[], b[], p[] may not intersect.
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        Zero length factors signify 0 significant bits: treat as 0.0.
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        0.0 factors do the right thing.
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        Zero length product OK.
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        I chose the ForTran accent "foo[bar]" instead of the C accent "*garply"
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        because I felt the ForTran way was more intuitive. The C way would
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        probably yield better code on most C compilers. Dean Elsner.
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        (C style also gives deeper insight [to me] ... oh well ...)  */
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void
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flonum_multip (const FLONUM_TYPE *a, const FLONUM_TYPE *b,
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               FLONUM_TYPE *product)
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{
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  int size_of_a;                /* 0 origin  */
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  int size_of_b;                /* 0 origin  */
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  int size_of_product;          /* 0 origin  */
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  int size_of_sum;              /* 0 origin  */
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  int extra_product_positions;  /* 1 origin  */
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  unsigned long work;
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  unsigned long carry;
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  long exponent;
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  LITTLENUM_TYPE *q;
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  long significant;             /* TRUE when we emit a non-0 littlenum  */
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  /* ForTran accent follows.  */
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  int P;                        /* Scan product low-order -> high.  */
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  int N;                        /* As in sum above.  */
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  int A;                        /* Which [] of a?  */
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  int B;                        /* Which [] of b?  */
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  if ((a->sign != '-' && a->sign != '+')
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      || (b->sign != '-' && b->sign != '+'))
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    {
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      /* Got to fail somehow.  Any suggestions?  */
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      product->sign = 0;
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      return;
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    }
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  product->sign = (a->sign == b->sign) ? '+' : '-';
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  size_of_a = a->leader - a->low;
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  size_of_b = b->leader - b->low;
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  exponent = a->exponent + b->exponent;
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  size_of_product = product->high - product->low;
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  size_of_sum = size_of_a + size_of_b;
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  extra_product_positions = size_of_product - size_of_sum;
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  if (extra_product_positions < 0)
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    {
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      P = extra_product_positions;      /* P < 0  */
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      exponent -= extra_product_positions;      /* Increases exponent.  */
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    }
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  else
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    {
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      P = 0;
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    }
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  carry = 0;
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  significant = 0;
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  for (N = 0; N <= size_of_sum; N++)
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    {
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      work = carry;
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      carry = 0;
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      for (A = 0; A <= N; A++)
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        {
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          B = N - A;
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          if (A <= size_of_a && B <= size_of_b && B >= 0)
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            {
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#ifdef TRACE
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              printf ("a:low[%d.]=%04x b:low[%d.]=%04x work_before=%08x\n",
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                      A, a->low[A], B, b->low[B], work);
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#endif
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              /* Watch out for sign extension!  Without the casts, on
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                 the DEC Alpha, the multiplication result is *signed*
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                 int, which gets sign-extended to convert to the
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                 unsigned long!  */
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              work += (unsigned long) a->low[A] * (unsigned long) b->low[B];
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              carry += work >> LITTLENUM_NUMBER_OF_BITS;
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              work &= LITTLENUM_MASK;
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#ifdef TRACE
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              printf ("work=%08x carry=%04x\n", work, carry);
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#endif
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            }
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        }
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      significant |= work;
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      if (significant || P < 0)
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        {
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          if (P >= 0)
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            {
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              product->low[P] = work;
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#ifdef TRACE
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              printf ("P=%d. work[p]:=%04x\n", P, work);
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#endif
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            }
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          P++;
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        }
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      else
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        {
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          extra_product_positions++;
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          exponent++;
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        }
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    }
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  /* [P]-> position # size_of_sum + 1.
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     This is where 'carry' should go.  */
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#ifdef TRACE
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  printf ("final carry =%04x\n", carry);
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#endif
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  if (carry)
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    {
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      if (extra_product_positions > 0)
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        product->low[P] = carry;
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      else
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        {
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          /* No room at high order for carry littlenum.  */
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          /* Shift right 1 to make room for most significant littlenum.  */
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          exponent++;
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          P--;
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          for (q = product->low + P; q >= product->low; q--)
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            {
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              work = *q;
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              *q = carry;
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              carry = work;
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            }
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        }
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    }
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  else
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    P--;
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  product->leader = product->low + P;
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  product->exponent = exponent;
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}

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