fsmul.c

sdcc是为51等小型嵌入式cpu设计的c语言编译器支持数种不同类型的cpu

/*
** libgcc support for software floating point.
** Copyright (C) 1991 by Pipeline Associates, Inc.  All rights reserved.
** Permission is granted to do *anything* you want with this file,
** commercial or otherwise, provided this message remains intact.  So there!
** I would appreciate receiving any updates/patches/changes that anyone
** makes, and am willing to be the repository for said changes (am I
** making a big mistake?).
**
** Pat Wood
** Pipeline Associates, Inc.
** pipeline![e-mail] or
** sun!pipeline!phw or
** uunet!motown!pipeline!phw
*/

/*
** $Id: fsmul.c 3513 2004-10-01 14:49:51Z vrokas $
*/

/* (c)2000/2001: hacked a little by [e-mail] for sdcc */

#include <float.h>

union float_long
  {
    float f;
    unsigned long l;
  };

/* multiply two floats */
float __fsmul (float a1, float a2) _FS_REENTRANT
{
  FS_STATIC volatile union float_long fl1, fl2;
  unsigned long result;
  int exp;
  char sign;
  
  fl1.f = a1;
  fl2.f = a2;

  if (!fl1.l || !fl2.l)
    return (0);

  /* compute sign and exponent */
  sign = SIGN (fl1.l) ^ SIGN (fl2.l);
  exp = EXP (fl1.l) - EXCESS;
  exp += EXP (fl2.l);

  fl1.l = MANT (fl1.l);
  fl2.l = MANT (fl2.l);

  /* the multiply is done as one 16x16 multiply and two 16x8 multiples */
  result = (fl1.l >> 8) * (fl2.l >> 8);
  result += ((fl1.l & (unsigned long) 0xFF) * (fl2.l >> 8)) >> 8;
  result += ((fl2.l & (unsigned long) 0xFF) * (fl1.l >> 8)) >> 8;

  if (0 != (result & SIGNBIT))
    {
      /* round */
      result += 0x80;
      result >>= 8;
    }
  else
    {
      /* round */
      result += 0x40;
      result >>= 7;
      exp--;
    }

  result &= ~HIDDEN;

  /* pack up and go home */
  if (exp >= 0x100)
    fl1.l = (sign ? SIGNBIT : 0) | 0x7F800000;
  else if (exp < 0)
    fl1.l = 0;
  else
    fl1.l = PACK (sign ? SIGNBIT : 0 , exp, result);
  return (fl1.f);
}