arch/alpha/lib/ev67-strlen_user.S

   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