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1da177e4 LT |
1 | /* |
2 | * arch/alpha/lib/ev67-strlen_user.S | |
3 | * 21264 version contributed by Rick Gorton <rick.gorton@api-networks.com> | |
4 | * | |
5 | * Return the length of the string including the NULL terminator | |
6 | * (strlen+1) or zero if an error occurred. | |
7 | * | |
8 | * In places where it is critical to limit the processing time, | |
9 | * and the data is not trusted, strnlen_user() should be used. | |
10 | * It will return a value greater than its second argument if | |
11 | * that limit would be exceeded. This implementation is allowed | |
12 | * to access memory beyond the limit, but will not cross a page | |
13 | * boundary when doing so. | |
14 | * | |
15 | * Much of the information about 21264 scheduling/coding comes from: | |
16 | * Compiler Writer's Guide for the Alpha 21264 | |
17 | * abbreviated as 'CWG' in other comments here | |
18 | * ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html | |
19 | * Scheduling notation: | |
20 | * E - either cluster | |
21 | * U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1 | |
22 | * L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1 | |
23 | * Try not to change the actual algorithm if possible for consistency. | |
24 | */ | |
25 | ||
26 | #include <asm/regdef.h> | |
27 | ||
28 | ||
29 | /* Allow an exception for an insn; exit if we get one. */ | |
30 | #define EX(x,y...) \ | |
31 | 99: x,##y; \ | |
32 | .section __ex_table,"a"; \ | |
33 | .long 99b - .; \ | |
34 | lda v0, $exception-99b(zero); \ | |
35 | .previous | |
36 | ||
37 | ||
38 | .set noreorder | |
39 | .set noat | |
40 | .text | |
41 | ||
42 | .globl __strlen_user | |
43 | .ent __strlen_user | |
44 | .frame sp, 0, ra | |
45 | ||
46 | .align 4 | |
47 | __strlen_user: | |
48 | ldah a1, 32767(zero) # do not use plain strlen_user() for strings | |
49 | # that might be almost 2 GB long; you should | |
50 | # be using strnlen_user() instead | |
51 | nop | |
52 | nop | |
53 | nop | |
54 | ||
55 | .globl __strnlen_user | |
56 | ||
57 | .align 4 | |
58 | __strnlen_user: | |
59 | .prologue 0 | |
60 | EX( ldq_u t0, 0(a0) ) # L : load first quadword (a0 may be misaligned) | |
61 | lda t1, -1(zero) # E : | |
62 | ||
63 | insqh t1, a0, t1 # U : | |
64 | andnot a0, 7, v0 # E : | |
65 | or t1, t0, t0 # E : | |
66 | subq a0, 1, a0 # E : get our +1 for the return | |
67 | ||
68 | cmpbge zero, t0, t1 # E : t1 <- bitmask: bit i == 1 <==> i-th byte == 0 | |
69 | subq a1, 7, t2 # E : | |
70 | subq a0, v0, t0 # E : | |
71 | bne t1, $found # U : | |
72 | ||
73 | addq t2, t0, t2 # E : | |
74 | addq a1, 1, a1 # E : | |
75 | nop # E : | |
76 | nop # E : | |
77 | ||
78 | .align 4 | |
79 | $loop: ble t2, $limit # U : | |
80 | EX( ldq t0, 8(v0) ) # L : | |
81 | nop # E : | |
82 | nop # E : | |
83 | ||
84 | cmpbge zero, t0, t1 # E : | |
85 | subq t2, 8, t2 # E : | |
86 | addq v0, 8, v0 # E : addr += 8 | |
87 | beq t1, $loop # U : | |
88 | ||
89 | $found: cttz t1, t2 # U0 : | |
90 | addq v0, t2, v0 # E : | |
91 | subq v0, a0, v0 # E : | |
92 | ret # L0 : | |
93 | ||
94 | $exception: | |
95 | nop | |
96 | nop | |
97 | nop | |
98 | ret | |
99 | ||
100 | .align 4 # currently redundant | |
101 | $limit: | |
102 | nop | |
103 | nop | |
104 | subq a1, t2, v0 | |
105 | ret | |
106 | ||
107 | .end __strlen_user |