1 |
2 | scale.sa 3.3 7/30/91
3 |
4 | The entry point sSCALE computes the destination operand
5 | scaled by the source operand. If the absolute value of
6 | the source operand is (>= 2^14) an overflow or underflow
7 | is returned.
8 |
9 | The entry point sscale is called from do_func to emulate
10 | the fscale unimplemented instruction.
11 |
12 | Input: Double-extended destination operand in FPTEMP,
13 | double-extended source operand in ETEMP.
14 |
15 | Output: The function returns scale(X,Y) to fp0.
16 |
17 | Modifies: fp0.
18 |
19 | Algorithm:
20 |
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24 | THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA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.
27
28 |SCALE idnt 2,1 | Motorola 040 Floating Point Software Package
29
30 |section 8
31
32 .include "fpsp.h"
33
34 |xref t_ovfl2
35 |xref t_unfl
36 |xref round
37 |xref t_resdnrm
38
39 SRC_BNDS: .short 0x3fff,0x400c
40
41 |
42 | This entry point is used by the unimplemented instruction exception
43 | handler.
44 |
45 |
46 |
47 | FSCALE
48 |
49 .global sscale
50 sscale:
51 fmovel #0,%fpcr |clr user enabled exc
52 clrl %d1
53 movew FPTEMP(%a6),%d1 |get dest exponent
54 smi L_SCR1(%a6) |use L_SCR1 to hold sign
55 andil #0x7fff,%d1 |strip sign
56 movew ETEMP(%a6),%d0 |check src bounds
57 andiw #0x7fff,%d0 |clr sign bit
58 cmp2w SRC_BNDS,%d0
59 bccs src_in
60 cmpiw #0x400c,%d0 |test for too large
61 bge src_out
62 |
63 | The source input is below 1, so we check for denormalized numbers
64 | and set unfl.
65 |
66 src_small:
67 moveb DTAG(%a6),%d0
68 andib #0xe0,%d0
69 tstb %d0
70 beqs no_denorm
71 st STORE_FLG(%a6) |dest already contains result
72 orl #unfl_mask,USER_FPSR(%a6) |set UNFL
73 den_done:
74 leal FPTEMP(%a6),%a0
75 bra t_resdnrm
76 no_denorm:
77 fmovel USER_FPCR(%a6),%FPCR
78 fmovex FPTEMP(%a6),%fp0 |simply return dest
79 rts
80
81
82 |
83 | Source is within 2^14 range. To perform the int operation,
84 | move it to d0.
85 |
86 src_in:
87 fmovex ETEMP(%a6),%fp0 |move in src for int
88 fmovel #rz_mode,%fpcr |force rz for src conversion
89 fmovel %fp0,%d0 |int src to d0
90 fmovel #0,%FPSR |clr status from above
91 tstw ETEMP(%a6) |check src sign
92 blt src_neg
93 |
94 | Source is positive. Add the src to the dest exponent.
95 | The result can be denormalized, if src = 0, or overflow,
96 | if the result of the add sets a bit in the upper word.
97 |
98 src_pos:
99 tstw %d1 |check for denorm
100 beq dst_dnrm
101 addl %d0,%d1 |add src to dest exp
102 beqs denorm |if zero, result is denorm
103 cmpil #0x7fff,%d1 |test for overflow
104 bges ovfl
105 tstb L_SCR1(%a6)
106 beqs spos_pos
107 orw #0x8000,%d1
108 spos_pos:
109 movew %d1,FPTEMP(%a6) |result in FPTEMP
110 fmovel USER_FPCR(%a6),%FPCR
111 fmovex FPTEMP(%a6),%fp0 |write result to fp0
112 rts
113 ovfl:
114 tstb L_SCR1(%a6)
115 beqs sovl_pos
116 orw #0x8000,%d1
117 sovl_pos:
118 movew FPTEMP(%a6),ETEMP(%a6) |result in ETEMP
119 movel FPTEMP_HI(%a6),ETEMP_HI(%a6)
120 movel FPTEMP_LO(%a6),ETEMP_LO(%a6)
121 bra t_ovfl2
122
123 denorm:
124 tstb L_SCR1(%a6)
125 beqs den_pos
126 orw #0x8000,%d1
127 den_pos:
128 tstl FPTEMP_HI(%a6) |check j bit
129 blts nden_exit |if set, not denorm
130 movew %d1,ETEMP(%a6) |input expected in ETEMP
131 movel FPTEMP_HI(%a6),ETEMP_HI(%a6)
132 movel FPTEMP_LO(%a6),ETEMP_LO(%a6)
133 orl #unfl_bit,USER_FPSR(%a6) |set unfl
134 leal ETEMP(%a6),%a0
135 bra t_resdnrm
136 nden_exit:
137 movew %d1,FPTEMP(%a6) |result in FPTEMP
138 fmovel USER_FPCR(%a6),%FPCR
139 fmovex FPTEMP(%a6),%fp0 |write result to fp0
140 rts
141
142 |
143 | Source is negative. Add the src to the dest exponent.
144 | (The result exponent will be reduced). The result can be
145 | denormalized.
146 |
147 src_neg:
148 addl %d0,%d1 |add src to dest
149 beqs denorm |if zero, result is denorm
150 blts fix_dnrm |if negative, result is
151 | ;needing denormalization
152 tstb L_SCR1(%a6)
153 beqs sneg_pos
154 orw #0x8000,%d1
155 sneg_pos:
156 movew %d1,FPTEMP(%a6) |result in FPTEMP
157 fmovel USER_FPCR(%a6),%FPCR
158 fmovex FPTEMP(%a6),%fp0 |write result to fp0
159 rts
160
161
162 |
163 | The result exponent is below denorm value. Test for catastrophic
164 | underflow and force zero if true. If not, try to shift the
165 | mantissa right until a zero exponent exists.
166 |
167 fix_dnrm:
168 cmpiw #0xffc0,%d1 |lower bound for normalization
169 blt fix_unfl |if lower, catastrophic unfl
170 movew %d1,%d0 |use d0 for exp
171 movel %d2,-(%a7) |free d2 for norm
172 movel FPTEMP_HI(%a6),%d1
173 movel FPTEMP_LO(%a6),%d2
174 clrl L_SCR2(%a6)
175 fix_loop:
176 addw #1,%d0 |drive d0 to 0
177 lsrl #1,%d1 |while shifting the
178 roxrl #1,%d2 |mantissa to the right
179 bccs no_carry
180 st L_SCR2(%a6) |use L_SCR2 to capture inex
181 no_carry:
182 tstw %d0 |it is finished when
183 blts fix_loop |d0 is zero or the mantissa
184 tstb L_SCR2(%a6)
185 beqs tst_zero
186 orl #unfl_inx_mask,USER_FPSR(%a6)
187 | ;set unfl, aunfl, ainex
188 |
189 | Test for zero. If zero, simply use fmove to return +/- zero
190 | to the fpu.
191 |
192 tst_zero:
193 clrw FPTEMP_EX(%a6)
194 tstb L_SCR1(%a6) |test for sign
195 beqs tst_con
196 orw #0x8000,FPTEMP_EX(%a6) |set sign bit
197 tst_con:
198 movel %d1,FPTEMP_HI(%a6)
199 movel %d2,FPTEMP_LO(%a6)
200 movel (%a7)+,%d2
201 tstl %d1
202 bnes not_zero
203 tstl FPTEMP_LO(%a6)
204 bnes not_zero
205 |
206 | Result is zero. Check for rounding mode to set lsb. If the
207 | mode is rp, and the zero is positive, return smallest denorm.
208 | If the mode is rm, and the zero is negative, return smallest
209 | negative denorm.
210 |
211 btstb #5,FPCR_MODE(%a6) |test if rm or rp
212 beqs no_dir
213 btstb #4,FPCR_MODE(%a6) |check which one
214 beqs zer_rm
215 zer_rp:
216 tstb L_SCR1(%a6) |check sign
217 bnes no_dir |if set, neg op, no inc
218 movel #1,FPTEMP_LO(%a6) |set lsb
219 bras sm_dnrm
220 zer_rm:
221 tstb L_SCR1(%a6) |check sign
222 beqs no_dir |if clr, neg op, no inc
223 movel #1,FPTEMP_LO(%a6) |set lsb
224 orl #neg_mask,USER_FPSR(%a6) |set N
225 bras sm_dnrm
226 no_dir:
227 fmovel USER_FPCR(%a6),%FPCR
228 fmovex FPTEMP(%a6),%fp0 |use fmove to set cc's
229 rts
230
231 |
232 | The rounding mode changed the zero to a smallest denorm. Call
233 | t_resdnrm with exceptional operand in ETEMP.
234 |
235 sm_dnrm:
236 movel FPTEMP_EX(%a6),ETEMP_EX(%a6)
237 movel FPTEMP_HI(%a6),ETEMP_HI(%a6)
238 movel FPTEMP_LO(%a6),ETEMP_LO(%a6)
239 leal ETEMP(%a6),%a0
240 bra t_resdnrm
241
242 |
243 | Result is still denormalized.
244 |
245 not_zero:
246 orl #unfl_mask,USER_FPSR(%a6) |set unfl
247 tstb L_SCR1(%a6) |check for sign
248 beqs fix_exit
249 orl #neg_mask,USER_FPSR(%a6) |set N
250 fix_exit:
251 bras sm_dnrm
252
253
254 |
255 | The result has underflowed to zero. Return zero and set
256 | unfl, aunfl, and ainex.
257 |
258 fix_unfl:
259 orl #unfl_inx_mask,USER_FPSR(%a6)
260 btstb #5,FPCR_MODE(%a6) |test if rm or rp
261 beqs no_dir2
262 btstb #4,FPCR_MODE(%a6) |check which one
263 beqs zer_rm2
264 zer_rp2:
265 tstb L_SCR1(%a6) |check sign
266 bnes no_dir2 |if set, neg op, no inc
267 clrl FPTEMP_EX(%a6)
268 clrl FPTEMP_HI(%a6)
269 movel #1,FPTEMP_LO(%a6) |set lsb
270 bras sm_dnrm |return smallest denorm
271 zer_rm2:
272 tstb L_SCR1(%a6) |check sign
273 beqs no_dir2 |if clr, neg op, no inc
274 movew #0x8000,FPTEMP_EX(%a6)
275 clrl FPTEMP_HI(%a6)
276 movel #1,FPTEMP_LO(%a6) |set lsb
277 orl #neg_mask,USER_FPSR(%a6) |set N
278 bra sm_dnrm |return smallest denorm
279
280 no_dir2:
281 tstb L_SCR1(%a6)
282 bges pos_zero
283 neg_zero:
284 clrl FP_SCR1(%a6) |clear the exceptional operand
285 clrl FP_SCR1+4(%a6) |for gen_except.
286 clrl FP_SCR1+8(%a6)
287 fmoves #0x80000000,%fp0
288 rts
289 pos_zero:
290 clrl FP_SCR1(%a6) |clear the exceptional operand
291 clrl FP_SCR1+4(%a6) |for gen_except.
292 clrl FP_SCR1+8(%a6)
293 fmoves #0x00000000,%fp0
294 rts
295
296 |
297 | The destination is a denormalized number. It must be handled
298 | by first shifting the bits in the mantissa until it is normalized,
299 | then adding the remainder of the source to the exponent.
300 |
301 dst_dnrm:
302 moveml %d2/%d3,-(%a7)
303 movew FPTEMP_EX(%a6),%d1
304 movel FPTEMP_HI(%a6),%d2
305 movel FPTEMP_LO(%a6),%d3
306 dst_loop:
307 tstl %d2 |test for normalized result
308 blts dst_norm |exit loop if so
309 tstl %d0 |otherwise, test shift count
310 beqs dst_fin |if zero, shifting is done
311 subil #1,%d0 |dec src
312 lsll #1,%d3
313 roxll #1,%d2
314 bras dst_loop
315 |
316 | Destination became normalized. Simply add the remaining
317 | portion of the src to the exponent.
318 |
319 dst_norm:
320 addw %d0,%d1 |dst is normalized; add src
321 tstb L_SCR1(%a6)
322 beqs dnrm_pos
323 orl #0x8000,%d1
324 dnrm_pos:
325 movemw %d1,FPTEMP_EX(%a6)
326 moveml %d2,FPTEMP_HI(%a6)
327 moveml %d3,FPTEMP_LO(%a6)
328 fmovel USER_FPCR(%a6),%FPCR
329 fmovex FPTEMP(%a6),%fp0
330 moveml (%a7)+,%d2/%d3
331 rts
332
333 |
334 | Destination remained denormalized. Call t_excdnrm with
335 | exceptional operand in ETEMP.
336 |
337 dst_fin:
338 tstb L_SCR1(%a6) |check for sign
339 beqs dst_exit
340 orl #neg_mask,USER_FPSR(%a6) |set N
341 orl #0x8000,%d1
342 dst_exit:
343 movemw %d1,ETEMP_EX(%a6)
344 moveml %d2,ETEMP_HI(%a6)
345 moveml %d3,ETEMP_LO(%a6)
346 orl #unfl_mask,USER_FPSR(%a6) |set unfl
347 moveml (%a7)+,%d2/%d3
348 leal ETEMP(%a6),%a0
349 bra t_resdnrm
350
351 |
352 | Source is outside of 2^14 range. Test the sign and branch
353 | to the appropriate exception handler.
354 |
355 src_out:
356 tstb L_SCR1(%a6)
357 beqs scro_pos
358 orl #0x8000,%d1
359 scro_pos:
360 movel FPTEMP_HI(%a6),ETEMP_HI(%a6)
361 movel FPTEMP_LO(%a6),ETEMP_LO(%a6)
362 tstw ETEMP(%a6)
363 blts res_neg
364 res_pos:
365 movew %d1,ETEMP(%a6) |result in ETEMP
366 bra t_ovfl2
367 res_neg:
368 movew %d1,ETEMP(%a6) |result in ETEMP
369 leal ETEMP(%a6),%a0
370 bra t_unfl
371 |end
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