| blob | 077fcc230fcc5fde1f1e4bd4df6ba54f9093f9e6 |
1 |
2 | x_unfl.sa 3.4 7/1/91
3 |
4 | fpsp_unfl --- FPSP handler for underflow exception
5 |
6 | Trap disabled results
7 | For 881/2 compatibility, sw must denormalize the intermediate
8 | result, then store the result. Denormalization is accomplished
9 | by taking the intermediate result (which is always normalized) and
10 | shifting the mantissa right while incrementing the exponent until
11 | it is equal to the denormalized exponent for the destination
12 | format. After denormalization, the result is rounded to the
13 | destination format.
14 |
15 | Trap enabled results
16 | All trap disabled code applies. In addition the exceptional
17 | operand needs to made available to the user with a bias of $6000
18 | added to the exponent.
19 |
21 | Copyright (C) Motorola, Inc. 1990
22 | All Rights Reserved
23 |
24 | THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA
25 | The copyright notice above does not evidence any
26 | actual or intended publication of such source code.
28 X_UNFL: |idnt 2,1 | Motorola 040 Floating Point Software Package
30 |section 8
32 #include "fpsp.h"
34 |xref denorm
35 |xref round
36 |xref store
37 |xref g_rndpr
38 |xref g_opcls
39 |xref g_dfmtou
40 |xref real_unfl
41 |xref real_inex
42 |xref fpsp_done
43 |xref b1238_fix
45 .global fpsp_unfl
46 fpsp_unfl:
47 link %a6,#-LOCAL_SIZE
48 fsave -(%a7)
49 moveml %d0-%d1/%a0-%a1,USER_DA(%a6)
50 fmovemx %fp0-%fp3,USER_FP0(%a6)
51 fmoveml %fpcr/%fpsr/%fpiar,USER_FPCR(%a6)
53 |
54 bsrl unf_res |denormalize, round & store interm op
55 |
56 | If underflow exceptions are not enabled, check for inexact
57 | exception
58 |
59 btstb #unfl_bit,FPCR_ENABLE(%a6)
60 beqs ck_inex
62 btstb #E3,E_BYTE(%a6)
63 beqs no_e3_1
64 |
65 | Clear dirty bit on dest resister in the frame before branching
66 | to b1238_fix.
67 |
68 bfextu CMDREG3B(%a6){#6:#3},%d0 |get dest reg no
69 bclrb %d0,FPR_DIRTY_BITS(%a6) |clr dest dirty bit
70 bsrl b1238_fix |test for bug1238 case
71 movel USER_FPSR(%a6),FPSR_SHADOW(%a6)
72 orl #sx_mask,E_BYTE(%a6)
73 no_e3_1:
74 moveml USER_DA(%a6),%d0-%d1/%a0-%a1
75 fmovemx USER_FP0(%a6),%fp0-%fp3
76 fmoveml USER_FPCR(%a6),%fpcr/%fpsr/%fpiar
77 frestore (%a7)+
78 unlk %a6
79 bral real_unfl
80 |
81 | It is possible to have either inex2 or inex1 exceptions with the
82 | unfl. If the inex enable bit is set in the FPCR, and either
83 | inex2 or inex1 occurred, we must clean up and branch to the
84 | real inex handler.
85 |
86 ck_inex:
87 moveb FPCR_ENABLE(%a6),%d0
88 andb FPSR_EXCEPT(%a6),%d0
89 andib #0x3,%d0
90 beqs unfl_done
92 |
93 | Inexact enabled and reported, and we must take an inexact exception
94 |
95 take_inex:
96 btstb #E3,E_BYTE(%a6)
97 beqs no_e3_2
98 |
99 | Clear dirty bit on dest resister in the frame before branching
100 | to b1238_fix.
101 |
102 bfextu CMDREG3B(%a6){#6:#3},%d0 |get dest reg no
103 bclrb %d0,FPR_DIRTY_BITS(%a6) |clr dest dirty bit
104 bsrl b1238_fix |test for bug1238 case
105 movel USER_FPSR(%a6),FPSR_SHADOW(%a6)
106 orl #sx_mask,E_BYTE(%a6)
107 no_e3_2:
108 moveb #INEX_VEC,EXC_VEC+1(%a6)
109 moveml USER_DA(%a6),%d0-%d1/%a0-%a1
110 fmovemx USER_FP0(%a6),%fp0-%fp3
111 fmoveml USER_FPCR(%a6),%fpcr/%fpsr/%fpiar
112 frestore (%a7)+
113 unlk %a6
114 bral real_inex
116 unfl_done:
117 bclrb #E3,E_BYTE(%a6)
118 beqs e1_set |if set then branch
119 |
120 | Clear dirty bit on dest resister in the frame before branching
121 | to b1238_fix.
122 |
123 bfextu CMDREG3B(%a6){#6:#3},%d0 |get dest reg no
124 bclrb %d0,FPR_DIRTY_BITS(%a6) |clr dest dirty bit
125 bsrl b1238_fix |test for bug1238 case
126 movel USER_FPSR(%a6),FPSR_SHADOW(%a6)
127 orl #sx_mask,E_BYTE(%a6)
128 moveml USER_DA(%a6),%d0-%d1/%a0-%a1
129 fmovemx USER_FP0(%a6),%fp0-%fp3
130 fmoveml USER_FPCR(%a6),%fpcr/%fpsr/%fpiar
131 frestore (%a7)+
132 unlk %a6
133 bral fpsp_done
134 e1_set:
135 moveml USER_DA(%a6),%d0-%d1/%a0-%a1
136 fmovemx USER_FP0(%a6),%fp0-%fp3
137 fmoveml USER_FPCR(%a6),%fpcr/%fpsr/%fpiar
138 unlk %a6
139 bral fpsp_done
140 |
141 | unf_res --- underflow result calculation
142 |
143 unf_res:
144 bsrl g_rndpr |returns RND_PREC in d0 0=ext,
145 | ;1=sgl, 2=dbl
146 | ;we need the RND_PREC in the
147 | ;upper word for round
148 movew #0,-(%a7)
149 movew %d0,-(%a7) |copy RND_PREC to stack
150 |
151 |
152 | If the exception bit set is E3, the exceptional operand from the
153 | fpu is in WBTEMP; else it is in FPTEMP.
154 |
155 btstb #E3,E_BYTE(%a6)
156 beqs unf_E1
157 unf_E3:
158 lea WBTEMP(%a6),%a0 |a0 now points to operand
159 |
160 | Test for fsgldiv and fsglmul. If the inst was one of these, then
161 | force the precision to extended for the denorm routine. Use
162 | the user's precision for the round routine.
163 |
164 movew CMDREG3B(%a6),%d1 |check for fsgldiv or fsglmul
165 andiw #0x7f,%d1
166 cmpiw #0x30,%d1 |check for sgldiv
167 beqs unf_sgl
168 cmpiw #0x33,%d1 |check for sglmul
169 bnes unf_cont |if not, use fpcr prec in round
170 unf_sgl:
171 clrl %d0
172 movew #0x1,(%a7) |override g_rndpr precision
173 | ;force single
174 bras unf_cont
175 unf_E1:
176 lea FPTEMP(%a6),%a0 |a0 now points to operand
177 unf_cont:
178 bclrb #sign_bit,LOCAL_EX(%a0) |clear sign bit
179 sne LOCAL_SGN(%a0) |store sign
181 bsrl denorm |returns denorm, a0 points to it
182 |
183 | WARNING:
184 | ;d0 has guard,round sticky bit
185 | ;make sure that it is not corrupted
186 | ;before it reaches the round subroutine
187 | ;also ensure that a0 isn't corrupted
189 |
190 | Set up d1 for round subroutine d1 contains the PREC/MODE
191 | information respectively on upper/lower register halves.
192 |
193 bfextu FPCR_MODE(%a6){#2:#2},%d1 |get mode from FPCR
194 | ;mode in lower d1
195 addl (%a7)+,%d1 |merge PREC/MODE
196 |
197 | WARNING: a0 and d0 are assumed to be intact between the denorm and
198 | round subroutines. All code between these two subroutines
199 | must not corrupt a0 and d0.
200 |
201 |
202 | Perform Round
203 | Input: a0 points to input operand
204 | d0{31:29} has guard, round, sticky
205 | d1{01:00} has rounding mode
206 | d1{17:16} has rounding precision
207 | Output: a0 points to rounded operand
208 |
210 bsrl round |returns rounded denorm at (a0)
211 |
212 | Differentiate between store to memory vs. store to register
213 |
214 unf_store:
215 bsrl g_opcls |returns opclass in d0{2:0}
216 cmpib #0x3,%d0
217 bnes not_opc011
218 |
219 | At this point, a store to memory is pending
220 |
221 opc011:
222 bsrl g_dfmtou
223 tstb %d0
224 beqs ext_opc011 |If extended, do not subtract
225 | ;If destination format is sgl/dbl,
226 tstb LOCAL_HI(%a0) |If rounded result is normal,don't
227 | ;subtract
228 bmis ext_opc011
229 subqw #1,LOCAL_EX(%a0) |account for denorm bias vs.
230 | ;normalized bias
231 | ; normalized denormalized
232 | ;single $7f $7e
233 | ;double $3ff $3fe
234 |
235 ext_opc011:
236 bsrl store |stores to memory
237 bras unf_done |finish up
239 |
240 | At this point, a store to a float register is pending
241 |
242 not_opc011:
243 bsrl store |stores to float register
244 | ;a0 is not corrupted on a store to a
245 | ;float register.
246 |
247 | Set the condition codes according to result
248 |
249 tstl LOCAL_HI(%a0) |check upper mantissa
250 bnes ck_sgn
251 tstl LOCAL_LO(%a0) |check lower mantissa
252 bnes ck_sgn
253 bsetb #z_bit,FPSR_CC(%a6) |set condition codes if zero
254 ck_sgn:
255 btstb #sign_bit,LOCAL_EX(%a0) |check the sign bit
256 beqs unf_done
257 bsetb #neg_bit,FPSR_CC(%a6)
259 |
260 | Finish.
261 |
262 unf_done:
263 btstb #inex2_bit,FPSR_EXCEPT(%a6)
264 beqs no_aunfl
265 bsetb #aunfl_bit,FPSR_AEXCEPT(%a6)
266 no_aunfl:
267 rts
269 |end