root/arch/alpha/lib/ev6-memchr.S

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * arch/alpha/lib/ev6-memchr.S
   4  *
   5  * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com>
   6  *
   7  * Finds characters in a memory area.  Optimized for the Alpha:
   8  *
   9  *    - memory accessed as aligned quadwords only
  10  *    - uses cmpbge to compare 8 bytes in parallel
  11  *    - does binary search to find 0 byte in last
  12  *      quadword (HAKMEM needed 12 instructions to
  13  *      do this instead of the 9 instructions that
  14  *      binary search needs).
  15  *
  16  * For correctness consider that:
  17  *
  18  *    - only minimum number of quadwords may be accessed
  19  *    - the third argument is an unsigned long
  20  *
  21  * Much of the information about 21264 scheduling/coding comes from:
  22  *      Compiler Writer's Guide for the Alpha 21264
  23  *      abbreviated as 'CWG' in other comments here
  24  *      ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
  25  * Scheduling notation:
  26  *      E       - either cluster
  27  *      U       - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
  28  *      L       - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
  29  * Try not to change the actual algorithm if possible for consistency.
  30  */
  31 #include <asm/export.h>
  32         .set noreorder
  33         .set noat
  34 
  35         .align  4
  36         .globl memchr
  37         .ent memchr
  38 memchr:
  39         .frame $30,0,$26,0
  40         .prologue 0
  41 
  42         # Hack -- if someone passes in (size_t)-1, hoping to just
  43         # search til the end of the address space, we will overflow
  44         # below when we find the address of the last byte.  Given
  45         # that we will never have a 56-bit address space, cropping
  46         # the length is the easiest way to avoid trouble.
  47         zap     $18, 0x80, $5   # U : Bound length
  48         beq     $18, $not_found # U :
  49         ldq_u   $1, 0($16)      # L : load first quadword Latency=3
  50         and     $17, 0xff, $17  # E : L L U U : 00000000000000ch
  51 
  52         insbl   $17, 1, $2      # U : 000000000000ch00
  53         cmpult  $18, 9, $4      # E : small (< 1 quad) string?
  54         or      $2, $17, $17    # E : 000000000000chch
  55         lda     $3, -1($31)     # E : U L L U
  56 
  57         sll     $17, 16, $2     # U : 00000000chch0000
  58         addq    $16, $5, $5     # E : Max search address
  59         or      $2, $17, $17    # E : 00000000chchchch
  60         sll     $17, 32, $2     # U : U L L U : chchchch00000000
  61 
  62         or      $2, $17, $17    # E : chchchchchchchch
  63         extql   $1, $16, $7     # U : $7 is upper bits
  64         beq     $4, $first_quad # U :
  65         ldq_u   $6, -1($5)      # L : L U U L : eight or less bytes to search Latency=3
  66 
  67         extqh   $6, $16, $6     # U : 2 cycle stall for $6
  68         mov     $16, $0         # E :
  69         nop                     # E :
  70         or      $7, $6, $1      # E : L U L U $1 = quadword starting at $16
  71 
  72         # Deal with the case where at most 8 bytes remain to be searched
  73         # in $1.  E.g.:
  74         #       $18 = 6
  75         #       $1 = ????c6c5c4c3c2c1
  76 $last_quad:
  77         negq    $18, $6         # E :
  78         xor     $17, $1, $1     # E :
  79         srl     $3, $6, $6      # U : $6 = mask of $18 bits set
  80         cmpbge  $31, $1, $2     # E : L U L U
  81 
  82         nop
  83         nop
  84         and     $2, $6, $2      # E :
  85         beq     $2, $not_found  # U : U L U L
  86 
  87 $found_it:
  88 #ifdef CONFIG_ALPHA_EV67
  89         /*
  90          * Since we are guaranteed to have set one of the bits, we don't
  91          * have to worry about coming back with a 0x40 out of cttz...
  92          */
  93         cttz    $2, $3          # U0 :
  94         addq    $0, $3, $0      # E : All done
  95         nop                     # E :
  96         ret                     # L0 : L U L U
  97 #else
  98         /*
  99          * Slow and clunky.  It can probably be improved.
 100          * An exercise left for others.
 101          */
 102         negq    $2, $3          # E :
 103         and     $2, $3, $2      # E :
 104         and     $2, 0x0f, $1    # E :
 105         addq    $0, 4, $3       # E :
 106 
 107         cmoveq  $1, $3, $0      # E : Latency 2, extra map cycle
 108         nop                     # E : keep with cmov
 109         and     $2, 0x33, $1    # E :
 110         addq    $0, 2, $3       # E : U L U L : 2 cycle stall on $0
 111 
 112         cmoveq  $1, $3, $0      # E : Latency 2, extra map cycle
 113         nop                     # E : keep with cmov
 114         and     $2, 0x55, $1    # E :
 115         addq    $0, 1, $3       # E : U L U L : 2 cycle stall on $0
 116 
 117         cmoveq  $1, $3, $0      # E : Latency 2, extra map cycle
 118         nop
 119         nop
 120         ret                     # L0 : L U L U
 121 #endif
 122 
 123         # Deal with the case where $18 > 8 bytes remain to be
 124         # searched.  $16 may not be aligned.
 125         .align 4
 126 $first_quad:
 127         andnot  $16, 0x7, $0    # E :
 128         insqh   $3, $16, $2     # U : $2 = 0000ffffffffffff ($16<0:2> ff)
 129         xor     $1, $17, $1     # E :
 130         or      $1, $2, $1      # E : U L U L $1 = ====ffffffffffff
 131 
 132         cmpbge  $31, $1, $2     # E :
 133         bne     $2, $found_it   # U :
 134         # At least one byte left to process.
 135         ldq     $1, 8($0)       # L :
 136         subq    $5, 1, $18      # E : U L U L
 137 
 138         addq    $0, 8, $0       # E :
 139         # Make $18 point to last quad to be accessed (the
 140         # last quad may or may not be partial).
 141         andnot  $18, 0x7, $18   # E :
 142         cmpult  $0, $18, $2     # E :
 143         beq     $2, $final      # U : U L U L
 144 
 145         # At least two quads remain to be accessed.
 146 
 147         subq    $18, $0, $4     # E : $4 <- nr quads to be processed
 148         and     $4, 8, $4       # E : odd number of quads?
 149         bne     $4, $odd_quad_count # U :
 150         # At least three quads remain to be accessed
 151         mov     $1, $4          # E : L U L U : move prefetched value to correct reg
 152 
 153         .align  4
 154 $unrolled_loop:
 155         ldq     $1, 8($0)       # L : prefetch $1
 156         xor     $17, $4, $2     # E :
 157         cmpbge  $31, $2, $2     # E :
 158         bne     $2, $found_it   # U : U L U L
 159 
 160         addq    $0, 8, $0       # E :
 161         nop                     # E :
 162         nop                     # E :
 163         nop                     # E :
 164 
 165 $odd_quad_count:
 166         xor     $17, $1, $2     # E :
 167         ldq     $4, 8($0)       # L : prefetch $4
 168         cmpbge  $31, $2, $2     # E :
 169         addq    $0, 8, $6       # E :
 170 
 171         bne     $2, $found_it   # U :
 172         cmpult  $6, $18, $6     # E :
 173         addq    $0, 8, $0       # E :
 174         nop                     # E :
 175 
 176         bne     $6, $unrolled_loop # U :
 177         mov     $4, $1          # E : move prefetched value into $1
 178         nop                     # E :
 179         nop                     # E :
 180 
 181 $final: subq    $5, $0, $18     # E : $18 <- number of bytes left to do
 182         nop                     # E :
 183         nop                     # E :
 184         bne     $18, $last_quad # U :
 185 
 186 $not_found:
 187         mov     $31, $0         # E :
 188         nop                     # E :
 189         nop                     # E :
 190         ret                     # L0 :
 191 
 192         .end memchr
 193         EXPORT_SYMBOL(memchr)