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Linux/arch/x86/math-emu/reg_mul.c

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  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 }
117 

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