arch/x86/math-emu/reg_mul.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*---------------------------------------------------------------------------+
   3  |  reg_mul.c                                                                |
   4  |                                                                           |
   5  | Multiply one FPU_REG by another, put the result in a destination FPU_REG. |
   6  |                                                                           |
   7  | Copyright (C) 1992,1993,1997                                              |
   8  |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
   9  |                  E-mail   billm@suburbia.net                              |
  10  |                                                                           |
  11  | Returns the tag of the result if no exceptions or errors occurred.        |
  12  |                                                                           |
  13  +---------------------------------------------------------------------------*/
  14
  15 /*---------------------------------------------------------------------------+
  16  | The destination may be any FPU_REG, including one of the source FPU_REGs. |
  17  +---------------------------------------------------------------------------*/
  18
  19 #include "fpu_emu.h"
  20 #include "exception.h"
  21 #include "reg_constant.h"
  22 #include "fpu_system.h"
  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         if (!(taga | tagb)) {
  40                 /* Both regs Valid, this should be the most common case. */
  41
  42                 tag =
  43                     FPU_u_mul(a, b, dest, control_w, sign,
  44                               exponent(a) + exponent(b));
  45                 if (tag < 0) {
  46                         setsign(dest, saved_sign);
  47                         return tag;
  48                 }
  49                 FPU_settagi(deststnr, tag);
  50                 return tag;
  51         }
  52
  53         if (taga == TAG_Special)
  54                 taga = FPU_Special(a);
  55         if (tagb == TAG_Special)
  56                 tagb = FPU_Special(b);
  57
  58         if (((taga == TAG_Valid) && (tagb == TW_Denormal))
  59             || ((taga == TW_Denormal) && (tagb == TAG_Valid))
  60             || ((taga == TW_Denormal) && (tagb == TW_Denormal))) {
  61                 FPU_REG x, y;
  62                 if (denormal_operand() < 0)
  63                         return FPU_Exception;
  64
  65                 FPU_to_exp16(a, &x);
  66                 FPU_to_exp16(b, &y);
  67                 tag = FPU_u_mul(&x, &y, dest, control_w, sign,
  68                                 exponent16(&x) + exponent16(&y));
  69                 if (tag < 0) {
  70                         setsign(dest, saved_sign);
  71                         return tag;
  72                 }
  73                 FPU_settagi(deststnr, tag);
  74                 return tag;
  75         } else if ((taga <= TW_Denormal) && (tagb <= TW_Denormal)) {
  76                 if (((tagb == TW_Denormal) || (taga == TW_Denormal))
  77                     && (denormal_operand() < 0))
  78                         return FPU_Exception;
  79
  80                 /* Must have either both arguments == zero, or
  81                    one valid and the other zero.
  82                    The result is therefore zero. */
  83                 FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);
  84                 /* The 80486 book says that the answer is +0, but a real
  85                    80486 behaves this way.
  86                    IEEE-754 apparently says it should be this way. */
  87                 setsign(dest, sign);
  88                 return TAG_Zero;
  89         }
  90         /* Must have infinities, NaNs, etc */
  91         else if ((taga == TW_NaN) || (tagb == TW_NaN)) {
  92                 return real_2op_NaN(b, tagb, deststnr, &st(0));
  93         } else if (((taga == TW_Infinity) && (tagb == TAG_Zero))
  94                    || ((tagb == TW_Infinity) && (taga == TAG_Zero))) {
  95                 return arith_invalid(deststnr); /* Zero*Infinity is invalid */
  96         } else if (((taga == TW_Denormal) || (tagb == TW_Denormal))
  97                    && (denormal_operand() < 0)) {
  98                 return FPU_Exception;
  99         } else if (taga == TW_Infinity) {
 100                 FPU_copy_to_regi(a, TAG_Special, deststnr);
 101                 setsign(dest, sign);
 102                 return TAG_Special;
 103         } else if (tagb == TW_Infinity) {
 104                 FPU_copy_to_regi(b, TAG_Special, deststnr);
 105                 setsign(dest, sign);
 106                 return TAG_Special;
 107         }
 108 #ifdef PARANOID
 109         else {
 110                 EXCEPTION(EX_INTERNAL | 0x102);
 111                 return FPU_Exception;
 112         }
 113 #endif /* PARANOID */
 114
 115         return 0;
 116 }