1   /* This file is generated from divrem.m4; DO NOT EDIT! */
2/*
3 * Division and remainder, from Appendix E of the Sparc Version 8
4 * Architecture Manual, with fixes from Gordon Irlam.
5 */
6
7/*
8 * Input: dividend and divisor in %o0 and %o1 respectively.
9 *
10 * m4 parameters:
11 *  .urem	name of function to generate
12 *  rem		rem=div => %o0 / %o1; rem=rem => %o0 % %o1
13 *  false		false=true => signed; false=false => unsigned
14 *
15 * Algorithm parameters:
16 *  N		how many bits per iteration we try to get (4)
17 *  WORDSIZE	total number of bits (32)
18 *
19 * Derived constants:
20 *  TOPBITS	number of bits in the top decade of a number
21 *
22 * Important variables:
23 *  Q		the partial quotient under development (initially 0)
24 *  R		the remainder so far, initially the dividend
25 *  ITER	number of main division loop iterations required;
26 *		equal to ceil(log2(quotient) / N).  Note that this
27 *		is the log base (2^N) of the quotient.
28 *  V		the current comparand, initially divisor*2^(ITER*N-1)
29 *
30 * Cost:
31 *  Current estimate for non-large dividend is
32 *	ceil(log2(quotient) / N) * (10 + 7N/2) + C
33 *  A large dividend is one greater than 2^(31-TOPBITS) and takes a
34 *  different path, as the upper bits of the quotient must be developed
35 *  one bit at a time.
36 */
37
38
39
40ENTRY(.urem)
41
42	! Ready to divide.  Compute size of quotient; scale comparand.
43	orcc	%o1, %g0, %o5
44	bne	1f
45	mov	%o0, %o3
46
47		! Divide by zero trap.  If it returns, return 0 (about as
48		! wrong as possible, but that is what SunOS does...).
49		ta	ST_DIV0
50		retl
51		clr	%o0
52
531:
54	cmp	%o3, %o5			! if %o1 exceeds %o0, done
55	blu	LOC(got_result)		! (and algorithm fails otherwise)
56	clr	%o2
57	sethi	%hi(1 << (32 - 4 - 1)), %g1
58	cmp	%o3, %g1
59	blu	LOC(not_really_big)
60	clr	%o4
61
62	! Here the dividend is >= 2**(31-N) or so.  We must be careful here,
63	! as our usual N-at-a-shot divide step will cause overflow and havoc.
64	! The number of bits in the result here is N*ITER+SC, where SC <= N.
65	! Compute ITER in an unorthodox manner: know we need to shift V into
66	! the top decade: so do not even bother to compare to R.
67	1:
68		cmp	%o5, %g1
69		bgeu	3f
70		mov	1, %g2
71		sll	%o5, 4, %o5
72		b	1b
73		add	%o4, 1, %o4
74
75	! Now compute %g2.
76	2:	addcc	%o5, %o5, %o5
77		bcc	LOC(not_too_big)
78		add	%g2, 1, %g2
79
80		! We get here if the %o1 overflowed while shifting.
81		! This means that %o3 has the high-order bit set.
82		! Restore %o5 and subtract from %o3.
83		sll	%g1, 4, %g1	! high order bit
84		srl	%o5, 1, %o5		! rest of %o5
85		add	%o5, %g1, %o5
86		b	LOC(do_single_div)
87		sub	%g2, 1, %g2
88
89	LOC(not_too_big):
90	3:	cmp	%o5, %o3
91		blu	2b
92		nop
93		be	LOC(do_single_div)
94		nop
95	/* NB: these are commented out in the V8-Sparc manual as well */
96	/* (I do not understand this) */
97	! %o5 > %o3: went too far: back up 1 step
98	!	srl	%o5, 1, %o5
99	!	dec	%g2
100	! do single-bit divide steps
101	!
102	! We have to be careful here.  We know that %o3 >= %o5, so we can do the
103	! first divide step without thinking.  BUT, the others are conditional,
104	! and are only done if %o3 >= 0.  Because both %o3 and %o5 may have the high-
105	! order bit set in the first step, just falling into the regular
106	! division loop will mess up the first time around.
107	! So we unroll slightly...
108	LOC(do_single_div):
109		subcc	%g2, 1, %g2
110		bl	LOC(end_regular_divide)
111		nop
112		sub	%o3, %o5, %o3
113		mov	1, %o2
114		b	LOC(end_single_divloop)
115		nop
116	LOC(single_divloop):
117		sll	%o2, 1, %o2
118		bl	1f
119		srl	%o5, 1, %o5
120		! %o3 >= 0
121		sub	%o3, %o5, %o3
122		b	2f
123		add	%o2, 1, %o2
124	1:	! %o3 < 0
125		add	%o3, %o5, %o3
126		sub	%o2, 1, %o2
127	2:
128	LOC(end_single_divloop):
129		subcc	%g2, 1, %g2
130		bge	LOC(single_divloop)
131		tst	%o3
132		b,a	LOC(end_regular_divide)
133
134LOC(not_really_big):
1351:
136	sll	%o5, 4, %o5
137	cmp	%o5, %o3
138	bleu	1b
139	addcc	%o4, 1, %o4
140	be	LOC(got_result)
141	sub	%o4, 1, %o4
142
143	tst	%o3	! set up for initial iteration
144LOC(divloop):
145	sll	%o2, 4, %o2
146		! depth 1, accumulated bits 0
147	bl	LOC(1.16)
148	srl	%o5,1,%o5
149	! remainder is positive
150	subcc	%o3,%o5,%o3
151			! depth 2, accumulated bits 1
152	bl	LOC(2.17)
153	srl	%o5,1,%o5
154	! remainder is positive
155	subcc	%o3,%o5,%o3
156			! depth 3, accumulated bits 3
157	bl	LOC(3.19)
158	srl	%o5,1,%o5
159	! remainder is positive
160	subcc	%o3,%o5,%o3
161			! depth 4, accumulated bits 7
162	bl	LOC(4.23)
163	srl	%o5,1,%o5
164	! remainder is positive
165	subcc	%o3,%o5,%o3
166		b	9f
167		add	%o2, (7*2+1), %o2
168
169LOC(4.23):
170	! remainder is negative
171	addcc	%o3,%o5,%o3
172		b	9f
173		add	%o2, (7*2-1), %o2
174
175
176LOC(3.19):
177	! remainder is negative
178	addcc	%o3,%o5,%o3
179			! depth 4, accumulated bits 5
180	bl	LOC(4.21)
181	srl	%o5,1,%o5
182	! remainder is positive
183	subcc	%o3,%o5,%o3
184		b	9f
185		add	%o2, (5*2+1), %o2
186
187LOC(4.21):
188	! remainder is negative
189	addcc	%o3,%o5,%o3
190		b	9f
191		add	%o2, (5*2-1), %o2
192
193
194
195LOC(2.17):
196	! remainder is negative
197	addcc	%o3,%o5,%o3
198			! depth 3, accumulated bits 1
199	bl	LOC(3.17)
200	srl	%o5,1,%o5
201	! remainder is positive
202	subcc	%o3,%o5,%o3
203			! depth 4, accumulated bits 3
204	bl	LOC(4.19)
205	srl	%o5,1,%o5
206	! remainder is positive
207	subcc	%o3,%o5,%o3
208		b	9f
209		add	%o2, (3*2+1), %o2
210
211LOC(4.19):
212	! remainder is negative
213	addcc	%o3,%o5,%o3
214		b	9f
215		add	%o2, (3*2-1), %o2
216
217
218LOC(3.17):
219	! remainder is negative
220	addcc	%o3,%o5,%o3
221			! depth 4, accumulated bits 1
222	bl	LOC(4.17)
223	srl	%o5,1,%o5
224	! remainder is positive
225	subcc	%o3,%o5,%o3
226		b	9f
227		add	%o2, (1*2+1), %o2
228
229LOC(4.17):
230	! remainder is negative
231	addcc	%o3,%o5,%o3
232		b	9f
233		add	%o2, (1*2-1), %o2
234
235
236
237
238LOC(1.16):
239	! remainder is negative
240	addcc	%o3,%o5,%o3
241			! depth 2, accumulated bits -1
242	bl	LOC(2.15)
243	srl	%o5,1,%o5
244	! remainder is positive
245	subcc	%o3,%o5,%o3
246			! depth 3, accumulated bits -1
247	bl	LOC(3.15)
248	srl	%o5,1,%o5
249	! remainder is positive
250	subcc	%o3,%o5,%o3
251			! depth 4, accumulated bits -1
252	bl	LOC(4.15)
253	srl	%o5,1,%o5
254	! remainder is positive
255	subcc	%o3,%o5,%o3
256		b	9f
257		add	%o2, (-1*2+1), %o2
258
259LOC(4.15):
260	! remainder is negative
261	addcc	%o3,%o5,%o3
262		b	9f
263		add	%o2, (-1*2-1), %o2
264
265
266LOC(3.15):
267	! remainder is negative
268	addcc	%o3,%o5,%o3
269			! depth 4, accumulated bits -3
270	bl	LOC(4.13)
271	srl	%o5,1,%o5
272	! remainder is positive
273	subcc	%o3,%o5,%o3
274		b	9f
275		add	%o2, (-3*2+1), %o2
276
277LOC(4.13):
278	! remainder is negative
279	addcc	%o3,%o5,%o3
280		b	9f
281		add	%o2, (-3*2-1), %o2
282
283
284
285LOC(2.15):
286	! remainder is negative
287	addcc	%o3,%o5,%o3
288			! depth 3, accumulated bits -3
289	bl	LOC(3.13)
290	srl	%o5,1,%o5
291	! remainder is positive
292	subcc	%o3,%o5,%o3
293			! depth 4, accumulated bits -5
294	bl	LOC(4.11)
295	srl	%o5,1,%o5
296	! remainder is positive
297	subcc	%o3,%o5,%o3
298		b	9f
299		add	%o2, (-5*2+1), %o2
300
301LOC(4.11):
302	! remainder is negative
303	addcc	%o3,%o5,%o3
304		b	9f
305		add	%o2, (-5*2-1), %o2
306
307
308LOC(3.13):
309	! remainder is negative
310	addcc	%o3,%o5,%o3
311			! depth 4, accumulated bits -7
312	bl	LOC(4.9)
313	srl	%o5,1,%o5
314	! remainder is positive
315	subcc	%o3,%o5,%o3
316		b	9f
317		add	%o2, (-7*2+1), %o2
318
319LOC(4.9):
320	! remainder is negative
321	addcc	%o3,%o5,%o3
322		b	9f
323		add	%o2, (-7*2-1), %o2
324
325
326
327
328	9:
329LOC(end_regular_divide):
330	subcc	%o4, 1, %o4
331	bge	LOC(divloop)
332	tst	%o3
333	bl,a	LOC(got_result)
334	! non-restoring fixup here (one instruction only!)
335	add	%o3, %o1, %o3
336
337
338LOC(got_result):
339
340	retl
341	mov %o3, %o0
342
343END(.urem)
344