arch/i386/math-emu/reg_u_sub.S

   1         .file   "reg_u_sub.S"
   2 /*---------------------------------------------------------------------------+
   3  |  reg_u_sub.S                                                              |
   4  |                                                                           |
   5  | Core floating point subtraction routine.                                  |
   6  |                                                                           |
   7  | Copyright (C) 1992,1993,1995,1997                                         |
   8  |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
   9  |                  E-mail   billm@suburbia.net                              |
  10  |                                                                           |
  11  | Call from C as:                                                           |
  12  |    int FPU_u_sub(FPU_REG *arg1, FPU_REG *arg2, FPU_REG *answ,             |
  13  |                                                int control_w)             |
  14  |    Return value is the tag of the answer, or-ed with FPU_Exception if     |
  15  |    one was raised, or -1 on internal error.                               |
  16  |                                                                           |
  17  +---------------------------------------------------------------------------*/
  18
  19 /*
  20  |    Kernel subtraction routine FPU_u_sub(reg *arg1, reg *arg2, reg *answ).
  21  |    Takes two valid reg f.p. numbers (TAG_Valid), which are
  22  |    treated as unsigned numbers,
  23  |    and returns their difference as a TAG_Valid or TAG_Zero f.p.
  24  |    number.
  25  |    The first number (arg1) must be the larger.
  26  |    The returned number is normalized.
  27  |    Basic checks are performed if PARANOID is defined.
  28  */
  29
  30 #include "exception.h"
  31 #include "fpu_emu.h"
  32 #include "control_w.h"
  33
  34 .text
  35 ENTRY(FPU_u_sub)
  36         pushl   %ebp
  37         movl    %esp,%ebp
  38         pushl   %esi
  39         pushl   %edi
  40         pushl   %ebx
  41
  42         movl    PARAM1,%esi     /* source 1 */
  43         movl    PARAM2,%edi     /* source 2 */
  44
  45         movl    PARAM6,%ecx
  46         subl    PARAM7,%ecx     /* exp1 - exp2 */
  47
  48 #ifdef PARANOID
  49         /* source 2 is always smaller than source 1 */
  50         js      L_bugged_1
  51
  52         testl   $0x80000000,SIGH(%edi)  /* The args are assumed to be be normalized */
  53         je      L_bugged_2
  54
  55         testl   $0x80000000,SIGH(%esi)
  56         je      L_bugged_2
  57 #endif /* PARANOID */
  58
  59 /*--------------------------------------+
  60  |      Form a register holding the     |
  61  |      smaller number                  |
  62  +--------------------------------------*/
  63         movl    SIGH(%edi),%eax /* register ms word */
  64         movl    SIGL(%edi),%ebx /* register ls word */
  65
  66         movl    PARAM3,%edi     /* destination */
  67         movl    PARAM6,%edx
  68         movw    %dx,EXP(%edi)   /* Copy exponent to destination */
  69
  70         xorl    %edx,%edx       /* register extension */
  71
  72 /*--------------------------------------+
  73  |      Shift the temporary register    |
  74  |      right the required number of    |
  75  |      places.                         |
  76  +--------------------------------------*/
  77
  78         cmpw    $32,%cx         /* shrd only works for 0..31 bits */
  79         jnc     L_more_than_31
  80
  81 /* less than 32 bits */
  82         shrd    %cl,%ebx,%edx
  83         shrd    %cl,%eax,%ebx
  84         shr     %cl,%eax
  85         jmp     L_shift_done
  86
  87 L_more_than_31:
  88         cmpw    $64,%cx
  89         jnc     L_more_than_63
  90
  91         subb    $32,%cl
  92         jz      L_exactly_32
  93
  94         shrd    %cl,%eax,%edx
  95         shr     %cl,%eax
  96         orl     %ebx,%ebx
  97         jz      L_more_31_no_low        /* none of the lowest bits is set */
  98
  99         orl     $1,%edx                 /* record the fact in the extension */
 100
 101 L_more_31_no_low:
 102         movl    %eax,%ebx
 103         xorl    %eax,%eax
 104         jmp     L_shift_done
 105
 106 L_exactly_32:
 107         movl    %ebx,%edx
 108         movl    %eax,%ebx
 109         xorl    %eax,%eax
 110         jmp     L_shift_done
 111
 112 L_more_than_63:
 113         cmpw    $65,%cx
 114         jnc     L_more_than_64
 115
 116         /* Shift right by 64 bits */
 117         movl    %eax,%edx
 118         orl     %ebx,%ebx
 119         jz      L_more_63_no_low
 120
 121         orl     $1,%edx
 122         jmp     L_more_63_no_low
 123
 124 L_more_than_64:
 125         jne     L_more_than_65
 126
 127         /* Shift right by 65 bits */
 128         /* Carry is clear if we get here */
 129         movl    %eax,%edx
 130         rcrl    %edx
 131         jnc     L_shift_65_nc
 132
 133         orl     $1,%edx
 134         jmp     L_more_63_no_low
 135
 136 L_shift_65_nc:
 137         orl     %ebx,%ebx
 138         jz      L_more_63_no_low
 139
 140         orl     $1,%edx
 141         jmp     L_more_63_no_low
 142
 143 L_more_than_65:
 144         movl    $1,%edx         /* The shifted nr always at least one '1' */
 145
 146 L_more_63_no_low:
 147         xorl    %ebx,%ebx
 148         xorl    %eax,%eax
 149
 150 L_shift_done:
 151 L_subtr:
 152 /*------------------------------+
 153  |      Do the subtraction      |
 154  +------------------------------*/
 155         xorl    %ecx,%ecx
 156         subl    %edx,%ecx
 157         movl    %ecx,%edx
 158         movl    SIGL(%esi),%ecx
 159         sbbl    %ebx,%ecx
 160         movl    %ecx,%ebx
 161         movl    SIGH(%esi),%ecx
 162         sbbl    %eax,%ecx
 163         movl    %ecx,%eax
 164
 165 #ifdef PARANOID
 166         /* We can never get a borrow */
 167         jc      L_bugged
 168 #endif /* PARANOID */
 169
 170 /*--------------------------------------+
 171  |      Normalize the result            |
 172  +--------------------------------------*/
 173         testl   $0x80000000,%eax
 174         jnz     L_round         /* no shifting needed */
 175
 176         orl     %eax,%eax
 177         jnz     L_shift_1       /* shift left 1 - 31 bits */
 178
 179         orl     %ebx,%ebx
 180         jnz     L_shift_32      /* shift left 32 - 63 bits */
 181
 182 /*
 183  *       A rare case, the only one which is non-zero if we got here
 184  *         is:           1000000 .... 0000
 185  *                      -0111111 .... 1111 1
 186  *                       --------------------
 187  *                       0000000 .... 0000 1
 188  */
 189
 190         cmpl    $0x80000000,%edx
 191         jnz     L_must_be_zero
 192
 193         /* Shift left 64 bits */
 194         subw    $64,EXP(%edi)
 195         xchg    %edx,%eax
 196         jmp     fpu_reg_round
 197
 198 L_must_be_zero:
 199 #ifdef PARANOID
 200         orl     %edx,%edx
 201         jnz     L_bugged_3
 202 #endif /* PARANOID */
 203
 204         /* The result is zero */
 205         movw    $0,EXP(%edi)            /* exponent */
 206         movl    $0,SIGL(%edi)
 207         movl    $0,SIGH(%edi)
 208         movl    TAG_Zero,%eax
 209         jmp     L_exit
 210
 211 L_shift_32:
 212         movl    %ebx,%eax
 213         movl    %edx,%ebx
 214         movl    $0,%edx
 215         subw    $32,EXP(%edi)   /* Can get underflow here */
 216
 217 /* We need to shift left by 1 - 31 bits */
 218 L_shift_1:
 219         bsrl    %eax,%ecx       /* get the required shift in %ecx */
 220         subl    $31,%ecx
 221         negl    %ecx
 222         shld    %cl,%ebx,%eax
 223         shld    %cl,%edx,%ebx
 224         shl     %cl,%edx
 225         subw    %cx,EXP(%edi)   /* Can get underflow here */
 226
 227 L_round:
 228         jmp     fpu_reg_round   /* Round the result */
 229
 230
 231 #ifdef PARANOID
 232 L_bugged_1:
 233         pushl   EX_INTERNAL|0x206
 234         call    EXCEPTION
 235         pop     %ebx
 236         jmp     L_error_exit
 237
 238 L_bugged_2:
 239         pushl   EX_INTERNAL|0x209
 240         call    EXCEPTION
 241         pop     %ebx
 242         jmp     L_error_exit
 243
 244 L_bugged_3:
 245         pushl   EX_INTERNAL|0x210
 246         call    EXCEPTION
 247         pop     %ebx
 248         jmp     L_error_exit
 249
 250 L_bugged_4:
 251         pushl   EX_INTERNAL|0x211
 252         call    EXCEPTION
 253         pop     %ebx
 254         jmp     L_error_exit
 255
 256 L_bugged:
 257         pushl   EX_INTERNAL|0x212
 258         call    EXCEPTION
 259         pop     %ebx
 260         jmp     L_error_exit
 261
 262 L_error_exit:
 263         movl    $-1,%eax
 264
 265 #endif /* PARANOID */
 266
 267 L_exit:
 268         popl    %ebx
 269         popl    %edi
 270         popl    %esi
 271         leave
 272         ret