summaryrefslogtreecommitdiffstats
path: root/arch/blackfin/lib/udivsi3.S
blob: 357b63241f9705618828ae94e6995de247cf2b10 (plain)
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
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
/*
 * File:         arch/blackfin/lib/udivsi3.S
 * Based on:
 * Author:
 *
 * Created:
 * Description:
 *
 * Rev:          $Id: udivsi3.S 2795 2007-03-05 06:25:33Z cooloney $
 *
 * Modified:
 *               Copyright 2004-2006 Analog Devices Inc.
 *
 * Bugs:         Enter bugs at http://blackfin.uclinux.org/
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#define CARRY AC0

#ifdef CONFIG_ARITHMETIC_OPS_L1
.section .l1.text
#else
.text
#endif


.globl ___udivsi3;

___udivsi3:
  CC = R0 < R1 (IU);    /* If X < Y, always return 0 */
  IF CC JUMP .Lreturn_ident;

  R2 = R1 << 16;
  CC = R2 <= R0 (IU);
  IF CC JUMP .Lidents;

  R2 = R0 >> 31;       /* if X is a 31-bit number */
  R3 = R1 >> 15;       /* and Y is a 15-bit number */
  R2 = R2 | R3;        /* then it's okay to use the DIVQ builtins (fallthrough to fast)*/
  CC = R2;
  IF CC JUMP .Ly_16bit;

/* METHOD 1: FAST DIVQ
   We know we have a 31-bit dividend, and 15-bit divisor so we can use the
   simple divq approach (first setting AQ to 0 - implying unsigned division,
   then 16 DIVQ's).
*/

  AQ = CC;             /* Clear AQ (CC==0) */

/* ISR States: When dividing two integers (32.0/16.0) using divide primitives,
   we need to shift the dividend one bit to the left.
   We have already checked that we have a 31-bit number so we are safe to do
   that.
*/
  R0 <<= 1;
  DIVQ(R0, R1); // 1
  DIVQ(R0, R1); // 2
  DIVQ(R0, R1); // 3
  DIVQ(R0, R1); // 4
  DIVQ(R0, R1); // 5
  DIVQ(R0, R1); // 6
  DIVQ(R0, R1); // 7
  DIVQ(R0, R1); // 8
  DIVQ(R0, R1); // 9
  DIVQ(R0, R1); // 10
  DIVQ(R0, R1); // 11
  DIVQ(R0, R1); // 12
  DIVQ(R0, R1); // 13
  DIVQ(R0, R1); // 14
  DIVQ(R0, R1); // 15
  DIVQ(R0, R1); // 16
  R0 = R0.L (Z);
  RTS;

.Ly_16bit:
  /* We know that the upper 17 bits of Y might have bits set,
  ** or that the sign bit of X might have a bit. If Y is a
  ** 16-bit number, but not bigger, then we can use the builtins
  ** with a post-divide correction.
  ** R3 currently holds Y>>15, which means R3's LSB is the
  ** bit we're interested in.
  */

  /* According to the ISR, to use the Divide primitives for
  ** unsigned integer divide, the useable range is 31 bits
  */
  CC = ! BITTST(R0, 31);

  /* IF condition is true we can scale our inputs and use the divide primitives,
  ** with some post-adjustment
  */
  R3 += -1;		/* if so, Y is 0x00008nnn */
  CC &= AZ;

  /* If condition is true we can scale our inputs and use the divide primitives,
  ** with some post-adjustment
  */
  R3 = R1 >> 1;		/* Pre-scaled divisor for primitive case */
  R2 = R0 >> 16; 

  R2 = R3 - R2;		/* shifted divisor < upper 16 bits of dividend */
  CC &= CARRY;
  IF CC JUMP .Lshift_and_correct;

  /* Fall through to the identities */

/* METHOD 2: identities and manual calculation
   We are not able to use the divide primites, but may still catch some special
   cases.
*/
.Lidents:
  /* Test for common identities. Value to be returned is placed in R2. */
  CC = R0 == 0;        /* 0/Y => 0 */
  IF CC JUMP .Lreturn_r0;
  CC = R0 == R1;       /* X==Y => 1 */
  IF CC JUMP .Lreturn_ident;
  CC = R1 == 1;        /* X/1 => X */
  IF CC JUMP .Lreturn_ident;

  R2.L = ONES R1;
  R2 = R2.L (Z);
  CC = R2 == 1;
  IF CC JUMP .Lpower_of_two;

  [--SP] = (R7:5);                /* Push registers R5-R7 */

  /* Idents don't match. Go for the full operation. */


  R6 = 2;                         /* assume we'll shift two */
  R3 = 1;

  P2 = R1;
                                  /* If either R0 or R1 have sign set, */
                                  /* divide them by two, and note it's */
                                  /* been done. */
  CC = R1 < 0;
  R2 = R1 >> 1;
  IF CC R1 = R2;                  /* Possibly-shifted R1 */
  IF !CC R6 = R3;                 /* R1 doesn't, so at most 1 shifted */

  P0 = 0;
  R3 = -R1;
  [--SP] = R3;
  R2 = R0 >> 1;
  R2 = R0 >> 1;
  CC = R0 < 0;
  IF CC P0 = R6;                  /* Number of values divided */
  IF !CC R2 = R0;                 /* Shifted R0 */

                                  /* P0 is 0, 1 (NR/=2) or 2 (NR/=2, DR/=2) */

                                  /* r2 holds Copy dividend  */
  R3 = 0;                         /* Clear partial remainder */
  R7 = 0;                         /* Initialise quotient bit */

  P1 = 32;                        /* Set loop counter */
  LSETUP(.Lulst, .Lulend) LC0 = P1; /* Set loop counter */
.Lulst:  R6 = R2 >> 31;             /* R6 = sign bit of R2, for carry */
       R2 = R2 << 1;              /* Shift 64 bit dividend up by 1 bit */
       R3 = R3 << 1 || R5 = [SP];
       R3 = R3 | R6;              /* Include any carry */
       CC = R7 < 0;               /* Check quotient(AQ) */
                                  /* If AQ==0, we'll sub divisor */
       IF CC R5 = R1;             /* and if AQ==1, we'll add it. */
       R3 = R3 + R5;              /* Add/sub divsor to partial remainder */
       R7 = R3 ^ R1;              /* Generate next quotient bit */

       R5 = R7 >> 31;             /* Get AQ */
       BITTGL(R5, 0);             /* Invert it, to get what we'll shift */
.Lulend: R2 = R2 + R5;              /* and "shift" it in. */

  CC = P0 == 0;                   /* Check how many inputs we shifted */
  IF CC JUMP .Lno_mult;            /* if none... */
  R6 = R2 << 1;
  CC = P0 == 1;
  IF CC R2 = R6;                  /* if 1, Q = Q*2 */
  IF !CC R1 = P2;                 /* if 2, restore stored divisor */

  R3 = R2;                        /* Copy of R2 */
  R3 *= R1;                       /* Q * divisor */
  R5 = R0 - R3;                   /* Z = (dividend - Q * divisor) */
  CC = R1 <= R5 (IU);             /* Check if divisor <= Z? */
  R6 = CC;                        /* if yes, R6 = 1 */
  R2 = R2 + R6;                   /* if yes, add one to quotient(Q) */
.Lno_mult:
  SP += 4;
  (R7:5) = [SP++];                /* Pop registers R5-R7 */
  R0 = R2;                        /* Store quotient */
  RTS;

.Lreturn_ident:
  CC = R0 < R1 (IU);    /* If X < Y, always return 0 */
  R2 = 0;
  IF CC JUMP .Ltrue_return_ident;
  R2 = -1 (X);         /* X/0 => 0xFFFFFFFF */
  CC = R1 == 0;
  IF CC JUMP .Ltrue_return_ident;
  R2 = -R2;            /* R2 now 1 */
  CC = R0 == R1;       /* X==Y => 1 */
  IF CC JUMP .Ltrue_return_ident;
  R2 = R0;             /* X/1 => X */
  /*FALLTHRU*/

.Ltrue_return_ident:
  R0 = R2;
.Lreturn_r0:
  RTS;

.Lpower_of_two:
  /* Y has a single bit set, which means it's a power of two.
  ** That means we can perform the division just by shifting
  ** X to the right the appropriate number of bits
  */

  /* signbits returns the number of sign bits, minus one.
  ** 1=>30, 2=>29, ..., 0x40000000=>0. Which means we need
  ** to shift right n-signbits spaces. It also means 0x80000000
  ** is a special case, because that *also* gives a signbits of 0
  */

  R2 = R0 >> 31;
  CC = R1 < 0;
  IF CC JUMP .Ltrue_return_ident;

  R1.l = SIGNBITS R1;
  R1 = R1.L (Z);
  R1 += -30;
  R0 = LSHIFT R0 by R1.L;
  RTS;

/* METHOD 3: PRESCALE AND USE THE DIVIDE PRIMITIVES WITH SOME POST-CORRECTION
  Two scaling operations are required to use the divide primitives with a
  divisor > 0x7FFFF.
  Firstly (as in method 1) we need to shift the dividend 1 to the left for
  integer division.
  Secondly we need to shift both the divisor and dividend 1 to the right so
  both are in range for the primitives.
  The left/right shift of the dividend does nothing so we can skip it.
*/
.Lshift_and_correct:
  R2 = R0;
  // R3 is already R1 >> 1
  CC=!CC;
  AQ = CC;                        /* Clear AQ, got here with CC = 0 */
  DIVQ(R2, R3); // 1
  DIVQ(R2, R3); // 2
  DIVQ(R2, R3); // 3
  DIVQ(R2, R3); // 4
  DIVQ(R2, R3); // 5
  DIVQ(R2, R3); // 6
  DIVQ(R2, R3); // 7
  DIVQ(R2, R3); // 8
  DIVQ(R2, R3); // 9
  DIVQ(R2, R3); // 10
  DIVQ(R2, R3); // 11
  DIVQ(R2, R3); // 12
  DIVQ(R2, R3); // 13
  DIVQ(R2, R3); // 14
  DIVQ(R2, R3); // 15
  DIVQ(R2, R3); // 16

  /* According to the Instruction Set Reference:
     To divide by a divisor > 0x7FFF,
     1. prescale and perform divide to obtain quotient (Q) (done above),
     2. multiply quotient by unscaled divisor (result M)
     3. subtract the product from the divident to get an error (E = X - M)
     4. if E < divisor (Y) subtract 1, if E > divisor (Y) add 1, else return quotient (Q)
   */
  R3 = R2.L (Z);		/* Q = X' / Y' */
  R2 = R3;		/* Preserve Q */
  R2 *= R1;		/* M = Q * Y */
  R2 = R0 - R2;		/* E = X - M */
  R0 = R3;		/* Copy Q into result reg */

/* Correction: If result of the multiply is negative, we overflowed
   and need to correct the result by subtracting 1 from the result.*/
  R3 = 0xFFFF (Z);
  R2 = R2 >> 16;		/* E >> 16 */
  CC = R2 == R3;
  R3 = 1 ;
  R1 = R0 - R3;
  IF CC R0 = R1;
  RTS;