arch/i386/math-emu/reg_mul.c

   1 /*---------------------------------------------------------------------------+
   2  |  reg_mul.c                                                                |
   3  |                                                                           |
   4  | Multiply one FPU_REG by another, put the result in a destination FPU_REG. |
   5  |                                                                           |
   6  | Copyright (C) 1992,1993,1997                                              |
   7  |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
   8  |                  E-mail   billm@suburbia.net                              |
   9  |                                                                           |
  10  | Returns the tag of the result if no exceptions or errors occurred.        |
  11  |                                                                           |
  12  +---------------------------------------------------------------------------*/
  13
  14 /*---------------------------------------------------------------------------+
  15  | The destination may be any FPU_REG, including one of the source FPU_REGs. |
  16  +---------------------------------------------------------------------------*/
  17
  18 #include "fpu_emu.h"
  19 #include "exception.h"
  20 #include "reg_constant.h"
  21 #include "fpu_system.h"
  22
  23
  24 /*
  25   Multiply two registers to give a register result.
  26   The sources are st(deststnr) and (b,tagb,signb).
  27   The destination is st(deststnr).
  28   */
  29 /* This routine must be called with non-empty source registers */
  30 int FPU_mul(FPU_REG const *b, u_char tagb, int deststnr, int control_w)
  31 {
  32   FPU_REG *a = &st(deststnr);
  33   FPU_REG *dest = a;
  34   u_char taga = FPU_gettagi(deststnr);
  35   u_char saved_sign = getsign(dest);
  36   u_char sign = (getsign(a) ^ getsign(b));
  37   int tag;
  38
  39
  40   if ( !(taga | tagb) )
  41     {
  42       /* Both regs Valid, this should be the most common case. */
  43
  44       tag = FPU_u_mul(a, b, dest, control_w, sign, exponent(a) + exponent(b));
  45       if ( tag < 0 )
  46         {
  47           setsign(dest, saved_sign);
  48           return tag;
  49         }
  50       FPU_settagi(deststnr, tag);
  51       return tag;
  52     }
  53
  54   if ( taga == TAG_Special )
  55     taga = FPU_Special(a);
  56   if ( tagb == TAG_Special )
  57     tagb = FPU_Special(b);
  58
  59   if ( ((taga == TAG_Valid) && (tagb == TW_Denormal))
  60             || ((taga == TW_Denormal) && (tagb == TAG_Valid))
  61             || ((taga == TW_Denormal) && (tagb == TW_Denormal)) )
  62     {
  63       FPU_REG x, y;
  64       if ( denormal_operand() < 0 )
  65         return FPU_Exception;
  66
  67       FPU_to_exp16(a, &x);
  68       FPU_to_exp16(b, &y);
  69       tag = FPU_u_mul(&x, &y, dest, control_w, sign,
  70                       exponent16(&x) + exponent16(&y));
  71       if ( tag < 0 )
  72         {
  73           setsign(dest, saved_sign);
  74           return tag;
  75         }
  76       FPU_settagi(deststnr, tag);
  77       return tag;
  78     }
  79   else if ( (taga <= TW_Denormal) && (tagb <= TW_Denormal) )
  80     {
  81       if ( ((tagb == TW_Denormal) || (taga == TW_Denormal))
  82            && (denormal_operand() < 0) )
  83         return FPU_Exception;
  84
  85       /* Must have either both arguments == zero, or
  86          one valid and the other zero.
  87          The result is therefore zero. */
  88       FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);
  89       /* The 80486 book says that the answer is +0, but a real
  90          80486 behaves this way.
  91          IEEE-754 apparently says it should be this way. */
  92       setsign(dest, sign);
  93       return TAG_Zero;
  94     }
  95       /* Must have infinities, NaNs, etc */
  96   else if ( (taga == TW_NaN) || (tagb == TW_NaN) )
  97     {
  98       return real_2op_NaN(b, tagb, deststnr, &st(0));
  99     }
 100   else if ( ((taga == TW_Infinity) && (tagb == TAG_Zero))
 101             || ((tagb == TW_Infinity) && (taga == TAG_Zero)) )
 102     {
 103       return arith_invalid(deststnr);  /* Zero*Infinity is invalid */
 104     }
 105   else if ( ((taga == TW_Denormal) || (tagb == TW_Denormal))
 106             && (denormal_operand() < 0) )
 107     {
 108       return FPU_Exception;
 109     }
 110   else if (taga == TW_Infinity)
 111     {
 112       FPU_copy_to_regi(a, TAG_Special, deststnr);
 113       setsign(dest, sign);
 114       return TAG_Special;
 115     }
 116   else if (tagb == TW_Infinity)
 117     {
 118       FPU_copy_to_regi(b, TAG_Special, deststnr);
 119       setsign(dest, sign);
 120       return TAG_Special;
 121     }
 122
 123 #ifdef PARANOID
 124   else
 125     {
 126       EXCEPTION(EX_INTERNAL|0x102);
 127       return FPU_Exception;
 128     }
 129 #endif /* PARANOID */
 130
 131         return 0;
 132 }