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107 lines
2.5 KiB
107 lines
2.5 KiB
/*
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* arch/alpha/lib/ev67-strlen_user.S
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* 21264 version contributed by Rick Gorton <rick.gorton@api-networks.com>
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*
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* Return the length of the string including the NULL 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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* Much of the information about 21264 scheduling/coding comes from:
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* Compiler Writer's Guide for the Alpha 21264
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* abbreviated as 'CWG' in other comments here
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* ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
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* Scheduling notation:
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* E - either cluster
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* U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
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* L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
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* Try not to change the actual algorithm if possible for consistency.
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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 4
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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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nop
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nop
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nop
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.globl __strnlen_user
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.align 4
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__strnlen_user:
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.prologue 0
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EX( ldq_u t0, 0(a0) ) # L : load first quadword (a0 may be misaligned)
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lda t1, -1(zero) # E :
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insqh t1, a0, t1 # U :
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andnot a0, 7, v0 # E :
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or t1, t0, t0 # E :
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subq a0, 1, a0 # E : get our +1 for the return
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cmpbge zero, t0, t1 # E : t1 <- bitmask: bit i == 1 <==> i-th byte == 0
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subq a1, 7, t2 # E :
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subq a0, v0, t0 # E :
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bne t1, $found # U :
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addq t2, t0, t2 # E :
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addq a1, 1, a1 # E :
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nop # E :
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nop # E :
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.align 4
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$loop: ble t2, $limit # U :
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EX( ldq t0, 8(v0) ) # L :
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nop # E :
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nop # E :
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cmpbge zero, t0, t1 # E :
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subq t2, 8, t2 # E :
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addq v0, 8, v0 # E : addr += 8
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beq t1, $loop # U :
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$found: cttz t1, t2 # U0 :
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addq v0, t2, v0 # E :
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subq v0, a0, v0 # E :
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ret # L0 :
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$exception:
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nop
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nop
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nop
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ret
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.align 4 # currently redundant
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$limit:
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nop
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nop
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subq a1, t2, v0
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ret
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.end __strlen_user
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