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

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  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   Multiply two registers to give a register result.
 25   The sources are st(deststnr) and (b,tagb,signb).
 26   The destination is st(deststnr).
 27   */
 28 /* This routine must be called with non-empty source registers */
 29 int FPU_mul(FPU_REG const *b, u_char tagb, int deststnr, int control_w)
 30 {
 31         FPU_REG *a = &st(deststnr);
 32         FPU_REG *dest = a;
 33         u_char taga = FPU_gettagi(deststnr);
 34         u_char saved_sign = getsign(dest);
 35         u_char sign = (getsign(a) ^ getsign(b));
 36         int tag;
 37 
 38         if (!(taga | tagb)) {
 39                 /* Both regs Valid, this should be the most common case. */
 40 
 41                 tag =
 42                     FPU_u_mul(a, b, dest, control_w, sign,
 43                               exponent(a) + exponent(b));
 44                 if (tag < 0) {
 45                         setsign(dest, saved_sign);
 46                         return tag;
 47                 }
 48                 FPU_settagi(deststnr, tag);
 49                 return tag;
 50         }
 51 
 52         if (taga == TAG_Special)
 53                 taga = FPU_Special(a);
 54         if (tagb == TAG_Special)
 55                 tagb = FPU_Special(b);
 56 
 57         if (((taga == TAG_Valid) && (tagb == TW_Denormal))
 58             || ((taga == TW_Denormal) && (tagb == TAG_Valid))
 59             || ((taga == TW_Denormal) && (tagb == TW_Denormal))) {
 60                 FPU_REG x, y;
 61                 if (denormal_operand() < 0)
 62                         return FPU_Exception;
 63 
 64                 FPU_to_exp16(a, &x);
 65                 FPU_to_exp16(b, &y);
 66                 tag = FPU_u_mul(&x, &y, dest, control_w, sign,
 67                                 exponent16(&x) + exponent16(&y));
 68                 if (tag < 0) {
 69                         setsign(dest, saved_sign);
 70                         return tag;
 71                 }
 72                 FPU_settagi(deststnr, tag);
 73                 return tag;
 74         } else if ((taga <= TW_Denormal) && (tagb <= TW_Denormal)) {
 75                 if (((tagb == TW_Denormal) || (taga == TW_Denormal))
 76                     && (denormal_operand() < 0))
 77                         return FPU_Exception;
 78 
 79                 /* Must have either both arguments == zero, or
 80                    one valid and the other zero.
 81                    The result is therefore zero. */
 82                 FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);
 83                 /* The 80486 book says that the answer is +0, but a real
 84                    80486 behaves this way.
 85                    IEEE-754 apparently says it should be this way. */
 86                 setsign(dest, sign);
 87                 return TAG_Zero;
 88         }
 89         /* Must have infinities, NaNs, etc */
 90         else if ((taga == TW_NaN) || (tagb == TW_NaN)) {
 91                 return real_2op_NaN(b, tagb, deststnr, &st(0));
 92         } else if (((taga == TW_Infinity) && (tagb == TAG_Zero))
 93                    || ((tagb == TW_Infinity) && (taga == TAG_Zero))) {
 94                 return arith_invalid(deststnr); /* Zero*Infinity is invalid */
 95         } else if (((taga == TW_Denormal) || (tagb == TW_Denormal))
 96                    && (denormal_operand() < 0)) {
 97                 return FPU_Exception;
 98         } else if (taga == TW_Infinity) {
 99                 FPU_copy_to_regi(a, TAG_Special, deststnr);
100                 setsign(dest, sign);
101                 return TAG_Special;
102         } else if (tagb == TW_Infinity) {
103                 FPU_copy_to_regi(b, TAG_Special, deststnr);
104                 setsign(dest, sign);
105                 return TAG_Special;
106         }
107 #ifdef PARANOID
108         else {
109                 EXCEPTION(EX_INTERNAL | 0x102);
110                 return FPU_Exception;
111         }
112 #endif /* PARANOID */
113 
114         return 0;
115 }
116 

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