1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
|
.file "reg_u_sub.S"
/*---------------------------------------------------------------------------+
| reg_u_sub.S |
| |
| Core floating point subtraction routine. |
| |
| Copyright (C) 1992,1993,1995,1997 |
| W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
| E-mail billm@suburbia.net |
| |
| Call from C as: |
| int FPU_u_sub(FPU_REG *arg1, FPU_REG *arg2, FPU_REG *answ, |
| int control_w) |
| Return value is the tag of the answer, or-ed with FPU_Exception if |
| one was raised, or -1 on internal error. |
| |
+---------------------------------------------------------------------------*/
/*
| Kernel subtraction routine FPU_u_sub(reg *arg1, reg *arg2, reg *answ).
| Takes two valid reg f.p. numbers (TAG_Valid), which are
| treated as unsigned numbers,
| and returns their difference as a TAG_Valid or TAG_Zero f.p.
| number.
| The first number (arg1) must be the larger.
| The returned number is normalized.
| Basic checks are performed if PARANOID is defined.
*/
#include "exception.h"
#include "fpu_emu.h"
#include "control_w.h"
.text
ENTRY(FPU_u_sub)
pushl %ebp
movl %esp,%ebp
pushl %esi
pushl %edi
pushl %ebx
movl PARAM1,%esi /* source 1 */
movl PARAM2,%edi /* source 2 */
movl PARAM6,%ecx
subl PARAM7,%ecx /* exp1 - exp2 */
#ifdef PARANOID
/* source 2 is always smaller than source 1 */
js L_bugged_1
testl $0x80000000,SIGH(%edi) /* The args are assumed to be be normalized */
je L_bugged_2
testl $0x80000000,SIGH(%esi)
je L_bugged_2
#endif /* PARANOID */
/*--------------------------------------+
| Form a register holding the |
| smaller number |
+--------------------------------------*/
movl SIGH(%edi),%eax /* register ms word */
movl SIGL(%edi),%ebx /* register ls word */
movl PARAM3,%edi /* destination */
movl PARAM6,%edx
movw %dx,EXP(%edi) /* Copy exponent to destination */
xorl %edx,%edx /* register extension */
/*--------------------------------------+
| Shift the temporary register |
| right the required number of |
| places. |
+--------------------------------------*/
cmpw $32,%cx /* shrd only works for 0..31 bits */
jnc L_more_than_31
/* less than 32 bits */
shrd %cl,%ebx,%edx
shrd %cl,%eax,%ebx
shr %cl,%eax
jmp L_shift_done
L_more_than_31:
cmpw $64,%cx
jnc L_more_than_63
subb $32,%cl
jz L_exactly_32
shrd %cl,%eax,%edx
shr %cl,%eax
orl %ebx,%ebx
jz L_more_31_no_low /* none of the lowest bits is set */
orl $1,%edx /* record the fact in the extension */
L_more_31_no_low:
movl %eax,%ebx
xorl %eax,%eax
jmp L_shift_done
L_exactly_32:
movl %ebx,%edx
movl %eax,%ebx
xorl %eax,%eax
jmp L_shift_done
L_more_than_63:
cmpw $65,%cx
jnc L_more_than_64
/* Shift right by 64 bits */
movl %eax,%edx
orl %ebx,%ebx
jz L_more_63_no_low
orl $1,%edx
jmp L_more_63_no_low
L_more_than_64:
jne L_more_than_65
/* Shift right by 65 bits */
/* Carry is clear if we get here */
movl %eax,%edx
rcrl %edx
jnc L_shift_65_nc
orl $1,%edx
jmp L_more_63_no_low
L_shift_65_nc:
orl %ebx,%ebx
jz L_more_63_no_low
orl $1,%edx
jmp L_more_63_no_low
L_more_than_65:
movl $1,%edx /* The shifted nr always at least one '1' */
L_more_63_no_low:
xorl %ebx,%ebx
xorl %eax,%eax
L_shift_done:
L_subtr:
/*------------------------------+
| Do the subtraction |
+------------------------------*/
xorl %ecx,%ecx
subl %edx,%ecx
movl %ecx,%edx
movl SIGL(%esi),%ecx
sbbl %ebx,%ecx
movl %ecx,%ebx
movl SIGH(%esi),%ecx
sbbl %eax,%ecx
movl %ecx,%eax
#ifdef PARANOID
/* We can never get a borrow */
jc L_bugged
#endif /* PARANOID */
/*--------------------------------------+
| Normalize the result |
+--------------------------------------*/
testl $0x80000000,%eax
jnz L_round /* no shifting needed */
orl %eax,%eax
jnz L_shift_1 /* shift left 1 - 31 bits */
orl %ebx,%ebx
jnz L_shift_32 /* shift left 32 - 63 bits */
/*
* A rare case, the only one which is non-zero if we got here
* is: 1000000 .... 0000
* -0111111 .... 1111 1
* --------------------
* 0000000 .... 0000 1
*/
cmpl $0x80000000,%edx
jnz L_must_be_zero
/* Shift left 64 bits */
subw $64,EXP(%edi)
xchg %edx,%eax
jmp fpu_reg_round
L_must_be_zero:
#ifdef PARANOID
orl %edx,%edx
jnz L_bugged_3
#endif /* PARANOID */
/* The result is zero */
movw $0,EXP(%edi) /* exponent */
movl $0,SIGL(%edi)
movl $0,SIGH(%edi)
movl TAG_Zero,%eax
jmp L_exit
L_shift_32:
movl %ebx,%eax
movl %edx,%ebx
movl $0,%edx
subw $32,EXP(%edi) /* Can get underflow here */
/* We need to shift left by 1 - 31 bits */
L_shift_1:
bsrl %eax,%ecx /* get the required shift in %ecx */
subl $31,%ecx
negl %ecx
shld %cl,%ebx,%eax
shld %cl,%edx,%ebx
shl %cl,%edx
subw %cx,EXP(%edi) /* Can get underflow here */
L_round:
jmp fpu_reg_round /* Round the result */
#ifdef PARANOID
L_bugged_1:
pushl EX_INTERNAL|0x206
call EXCEPTION
pop %ebx
jmp L_error_exit
L_bugged_2:
pushl EX_INTERNAL|0x209
call EXCEPTION
pop %ebx
jmp L_error_exit
L_bugged_3:
pushl EX_INTERNAL|0x210
call EXCEPTION
pop %ebx
jmp L_error_exit
L_bugged_4:
pushl EX_INTERNAL|0x211
call EXCEPTION
pop %ebx
jmp L_error_exit
L_bugged:
pushl EX_INTERNAL|0x212
call EXCEPTION
pop %ebx
jmp L_error_exit
L_error_exit:
movl $-1,%eax
#endif /* PARANOID */
L_exit:
popl %ebx
popl %edi
popl %esi
leave
ret
ENDPROC(FPU_u_sub)
|
