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92 lines
1.9 KiB
92 lines
1.9 KiB
20 years ago
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/*
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* arch/alpha/lib/strlen_user.S
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*
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* Return the length of the string including the NUL terminator
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* (strlen+1) or zero if an error occurred.
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*
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* In places where it is critical to limit the processing time,
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* and the data is not trusted, strnlen_user() should be used.
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* It will return a value greater than its second argument if
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* that limit would be exceeded. This implementation is allowed
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* to access memory beyond the limit, but will not cross a page
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* boundary when doing so.
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*/
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#include <asm/regdef.h>
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/* Allow an exception for an insn; exit if we get one. */
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#define EX(x,y...) \
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99: x,##y; \
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.section __ex_table,"a"; \
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.long 99b - .; \
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lda v0, $exception-99b(zero); \
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.previous
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.set noreorder
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.set noat
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.text
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.globl __strlen_user
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.ent __strlen_user
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.frame sp, 0, ra
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.align 3
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__strlen_user:
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ldah a1, 32767(zero) # do not use plain strlen_user() for strings
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# that might be almost 2 GB long; you should
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# be using strnlen_user() instead
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.globl __strnlen_user
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.align 3
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__strnlen_user:
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.prologue 0
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EX( ldq_u t0, 0(a0) ) # load first quadword (a0 may be misaligned)
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lda t1, -1(zero)
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insqh t1, a0, t1
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andnot a0, 7, v0
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or t1, t0, t0
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subq a0, 1, a0 # get our +1 for the return
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cmpbge zero, t0, t1 # t1 <- bitmask: bit i == 1 <==> i-th byte == 0
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subq a1, 7, t2
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subq a0, v0, t0
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bne t1, $found
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addq t2, t0, t2
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addq a1, 1, a1
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.align 3
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$loop: ble t2, $limit
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EX( ldq t0, 8(v0) )
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subq t2, 8, t2
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addq v0, 8, v0 # addr += 8
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cmpbge zero, t0, t1
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beq t1, $loop
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$found: negq t1, t2 # clear all but least set bit
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and t1, t2, t1
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and t1, 0xf0, t2 # binary search for that set bit
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and t1, 0xcc, t3
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and t1, 0xaa, t4
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cmovne t2, 4, t2
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cmovne t3, 2, t3
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cmovne t4, 1, t4
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addq t2, t3, t2
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addq v0, t4, v0
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addq v0, t2, v0
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nop # dual issue next two on ev4 and ev5
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subq v0, a0, v0
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$exception:
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ret
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.align 3 # currently redundant
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$limit:
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subq a1, t2, v0
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ret
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.end __strlen_user
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