File: /usr/src/linux/arch/cris/lib/memset.c
1 /*#************************************************************************#*/
2 /*#-------------------------------------------------------------------------*/
3 /*# */
4 /*# FUNCTION NAME: memset() */
5 /*# */
6 /*# PARAMETERS: void* dst; Destination address. */
7 /*# int c; Value of byte to write. */
8 /*# int len; Number of bytes to write. */
9 /*# */
10 /*# RETURNS: dst. */
11 /*# */
12 /*# DESCRIPTION: Sets the memory dst of length len bytes to c, as standard. */
13 /*# Framework taken from memcpy. This routine is */
14 /*# very sensitive to compiler changes in register allocation. */
15 /*# Should really be rewritten to avoid this problem. */
16 /*# */
17 /*#-------------------------------------------------------------------------*/
18 /*# */
19 /*# HISTORY */
20 /*# */
21 /*# DATE NAME CHANGES */
22 /*# ---- ---- ------- */
23 /*# 990713 HP Tired of watching this function (or */
24 /*# really, the nonoptimized generic */
25 /*# implementation) take up 90% of simulator */
26 /*# output. Measurements needed. */
27 /*# */
28 /*#-------------------------------------------------------------------------*/
29
30 #include <linux/types.h>
31
32 /* No, there's no macro saying 12*4, since it is "hard" to get it into
33 the asm in a good way. Thus better to expose the problem everywhere.
34 */
35
36 /* Assuming 1 cycle per dword written or read (ok, not really true), and
37 one per instruction, then 43+3*(n/48-1) <= 24+24*(n/48-1)
38 so n >= 45.7; n >= 0.9; we win on the first full 48-byte block to set. */
39
40 #define ZERO_BLOCK_SIZE (1*12*4)
41
42 void *memset(void *pdst,
43 int c,
44 size_t plen)
45 {
46 /* Ok. Now we want the parameters put in special registers.
47 Make sure the compiler is able to make something useful of this. */
48
49 register char *return_dst __asm__ ("r10") = pdst;
50 register int n __asm__ ("r12") = plen;
51 register int lc __asm__ ("r11") = c;
52
53 /* Most apps use memset sanely. Only those memsetting about 3..4
54 bytes or less get penalized compared to the generic implementation
55 - and that's not really sane use. */
56
57 /* Ugh. This is fragile at best. Check with newer GCC releases, if
58 they compile cascaded "x |= x << 8" sanely! */
59 __asm__("movu.b %0,r13\n\t"
60 "lslq 8,r13\n\t"
61 "move.b %0,r13\n\t"
62 "move.d r13,%0\n\t"
63 "lslq 16,r13\n\t"
64 "or.d r13,%0"
65 : "=r" (lc) : "0" (lc) : "r13");
66
67 {
68 register char *dst __asm__ ("r13") = pdst;
69
70 /* This is NONPORTABLE, but since this whole routine is */
71 /* grossly nonportable that doesn't matter. */
72
73 if (((unsigned long) pdst & 3) != 0
74 /* Oops! n=0 must be a legal call, regardless of alignment. */
75 && n >= 3)
76 {
77 if ((unsigned long)dst & 1)
78 {
79 *dst = (char) lc;
80 n--;
81 dst++;
82 }
83
84 if ((unsigned long)dst & 2)
85 {
86 *(short *)dst = lc;
87 n -= 2;
88 dst += 2;
89 }
90 }
91
92 /* Now the fun part. For the threshold value of this, check the equation
93 above. */
94 /* Decide which copying method to use. */
95 if (n >= ZERO_BLOCK_SIZE)
96 {
97 /* For large copies we use 'movem' */
98
99 /* It is not optimal to tell the compiler about clobbering any
100 registers; that will move the saving/restoring of those registers
101 to the function prologue/epilogue, and make non-movem sizes
102 suboptimal.
103
104 This method is not foolproof; it assumes that the "asm reg"
105 declarations at the beginning of the function really are used
106 here (beware: they may be moved to temporary registers).
107 This way, we do not have to save/move the registers around into
108 temporaries; we can safely use them straight away.
109
110 If you want to check that the allocation was right; then
111 check the equalities in the first comment. It should say
112 "r13=r13, r12=r12, r11=r11" */
113 __asm__ volatile ("
114 ;; Check that the following is true (same register names on
115 ;; both sides of equal sign, as in r8=r8):
116 ;; %0=r13, %1=r12, %4=r11
117 ;;
118 ;; Save the registers we'll clobber in the movem process
119 ;; on the stack. Don't mention them to gcc, it will only be
120 ;; upset.
121 subq 11*4,sp
122 movem r10,[sp]
123
124 move.d r11,r0
125 move.d r11,r1
126 move.d r11,r2
127 move.d r11,r3
128 move.d r11,r4
129 move.d r11,r5
130 move.d r11,r6
131 move.d r11,r7
132 move.d r11,r8
133 move.d r11,r9
134 move.d r11,r10
135
136 ;; Now we've got this:
137 ;; r13 - dst
138 ;; r12 - n
139
140 ;; Update n for the first loop
141 subq 12*4,r12
142 0:
143 subq 12*4,r12
144 bge 0b
145 movem r11,[r13+]
146
147 addq 12*4,r12 ;; compensate for last loop underflowing n
148
149 ;; Restore registers from stack
150 movem [sp+],r10"
151
152 /* Outputs */ : "=r" (dst), "=r" (n)
153 /* Inputs */ : "0" (dst), "1" (n), "r" (lc));
154
155 }
156
157 /* Either we directly starts copying, using dword copying
158 in a loop, or we copy as much as possible with 'movem'
159 and then the last block (<44 bytes) is copied here.
160 This will work since 'movem' will have updated src,dst,n. */
161
162 while ( n >= 16 )
163 {
164 *((long*)dst)++ = lc;
165 *((long*)dst)++ = lc;
166 *((long*)dst)++ = lc;
167 *((long*)dst)++ = lc;
168 n -= 16;
169 }
170
171 /* A switch() is definitely the fastest although it takes a LOT of code.
172 * Particularly if you inline code this.
173 */
174 switch (n)
175 {
176 case 0:
177 break;
178 case 1:
179 *(char*)dst = (char) lc;
180 break;
181 case 2:
182 *(short*)dst = (short) lc;
183 break;
184 case 3:
185 *((short*)dst)++ = (short) lc;
186 *(char*)dst = (char) lc;
187 break;
188 case 4:
189 *((long*)dst)++ = lc;
190 break;
191 case 5:
192 *((long*)dst)++ = lc;
193 *(char*)dst = (char) lc;
194 break;
195 case 6:
196 *((long*)dst)++ = lc;
197 *(short*)dst = (short) lc;
198 break;
199 case 7:
200 *((long*)dst)++ = lc;
201 *((short*)dst)++ = (short) lc;
202 *(char*)dst = (char) lc;
203 break;
204 case 8:
205 *((long*)dst)++ = lc;
206 *((long*)dst)++ = lc;
207 break;
208 case 9:
209 *((long*)dst)++ = lc;
210 *((long*)dst)++ = lc;
211 *(char*)dst = (char) lc;
212 break;
213 case 10:
214 *((long*)dst)++ = lc;
215 *((long*)dst)++ = lc;
216 *(short*)dst = (short) lc;
217 break;
218 case 11:
219 *((long*)dst)++ = lc;
220 *((long*)dst)++ = lc;
221 *((short*)dst)++ = (short) lc;
222 *(char*)dst = (char) lc;
223 break;
224 case 12:
225 *((long*)dst)++ = lc;
226 *((long*)dst)++ = lc;
227 *((long*)dst)++ = lc;
228 break;
229 case 13:
230 *((long*)dst)++ = lc;
231 *((long*)dst)++ = lc;
232 *((long*)dst)++ = lc;
233 *(char*)dst = (char) lc;
234 break;
235 case 14:
236 *((long*)dst)++ = lc;
237 *((long*)dst)++ = lc;
238 *((long*)dst)++ = lc;
239 *(short*)dst = (short) lc;
240 break;
241 case 15:
242 *((long*)dst)++ = lc;
243 *((long*)dst)++ = lc;
244 *((long*)dst)++ = lc;
245 *((short*)dst)++ = (short) lc;
246 *(char*)dst = (char) lc;
247 break;
248 }
249 }
250
251 return return_dst; /* destination pointer. */
252 } /* memset() */
253