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/*
* arch/alpha/lib/ev67-strlen_user.S
* 21264 version contributed by Rick Gorton <rick.gorton@api-networks.com>
*
* Return the length of the string including the NULL terminator
* (strlen+1) or zero if an error occurred.
*
* In places where it is critical to limit the processing time,
* and the data is not trusted, strnlen_user() should be used.
* It will return a value greater than its second argument if
* that limit would be exceeded. This implementation is allowed
* to access memory beyond the limit, but will not cross a page
* boundary when doing so.
*
* Much of the information about 21264 scheduling/coding comes from:
* Compiler Writer's Guide for the Alpha 21264
* abbreviated as 'CWG' in other comments here
* ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
* Scheduling notation:
* E - either cluster
* U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
* L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
* Try not to change the actual algorithm if possible for consistency.
*/
#include <asm/regdef.h>
/* Allow an exception for an insn; exit if we get one. */
#define EX(x,y...) \
99: x,##y; \
.section __ex_table,"a"; \
.long 99b - .; \
lda v0, $exception-99b(zero); \
.previous
.set noreorder
.set noat
.text
.globl __strlen_user
.ent __strlen_user
.frame sp, 0, ra
.align 4
__strlen_user:
ldah a1, 32767(zero) # do not use plain strlen_user() for strings
# that might be almost 2 GB long; you should
# be using strnlen_user() instead
nop
nop
nop
.globl __strnlen_user
.align 4
__strnlen_user:
.prologue 0
EX( ldq_u t0, 0(a0) ) # L : load first quadword (a0 may be misaligned)
lda t1, -1(zero) # E :
insqh t1, a0, t1 # U :
andnot a0, 7, v0 # E :
or t1, t0, t0 # E :
subq a0, 1, a0 # E : get our +1 for the return
cmpbge zero, t0, t1 # E : t1 <- bitmask: bit i == 1 <==> i-th byte == 0
subq a1, 7, t2 # E :
subq a0, v0, t0 # E :
bne t1, $found # U :
addq t2, t0, t2 # E :
addq a1, 1, a1 # E :
nop # E :
nop # E :
.align 4
$loop: ble t2, $limit # U :
EX( ldq t0, 8(v0) ) # L :
nop # E :
nop # E :
cmpbge zero, t0, t1 # E :
subq t2, 8, t2 # E :
addq v0, 8, v0 # E : addr += 8
beq t1, $loop # U :
$found: cttz t1, t2 # U0 :
addq v0, t2, v0 # E :
subq v0, a0, v0 # E :
ret # L0 :
$exception:
nop
nop
nop
ret
.align 4 # currently redundant
$limit:
nop
nop
subq a1, t2, v0
ret
.end __strlen_user
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