root/arch/alpha/lib/ev67-strchr.S

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * arch/alpha/lib/ev67-strchr.S
   4  * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com>
   5  *
   6  * Return the address of a given character within a null-terminated
   7  * string, or null if it is not found.
   8  *
   9  * Much of the information about 21264 scheduling/coding comes from:
  10  *      Compiler Writer's Guide for the Alpha 21264
  11  *      abbreviated as 'CWG' in other comments here
  12  *      ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
  13  * Scheduling notation:
  14  *      E       - either cluster
  15  *      U       - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
  16  *      L       - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
  17  * Try not to change the actual algorithm if possible for consistency.
  18  */
  19 #include <asm/export.h>
  20 #include <asm/regdef.h>
  21 
  22         .set noreorder
  23         .set noat
  24 
  25         .align 4
  26         .globl strchr
  27         .ent strchr
  28 strchr:
  29         .frame sp, 0, ra
  30         .prologue 0
  31 
  32         ldq_u   t0, 0(a0)       # L : load first quadword Latency=3
  33         and     a1, 0xff, t3    # E : 00000000000000ch
  34         insbl   a1, 1, t5       # U : 000000000000ch00
  35         insbl   a1, 7, a2       # U : ch00000000000000
  36 
  37         insbl   t3, 6, a3       # U : 00ch000000000000
  38         or      t5, t3, a1      # E : 000000000000chch
  39         andnot  a0, 7, v0       # E : align our loop pointer
  40         lda     t4, -1          # E : build garbage mask
  41 
  42         mskqh   t4, a0, t4      # U : only want relevant part of first quad
  43         or      a2, a3, a2      # E : chch000000000000
  44         inswl   a1, 2, t5       # E : 00000000chch0000
  45         inswl   a1, 4, a3       # E : 0000chch00000000
  46 
  47         or      a1, a2, a1      # E : chch00000000chch
  48         or      a3, t5, t5      # E : 0000chchchch0000
  49         cmpbge  zero, t0, t2    # E : bits set iff byte == zero
  50         cmpbge  zero, t4, t4    # E : bits set iff byte is garbage
  51 
  52         /* This quad is _very_ serialized.  Lots of stalling happens */
  53         or      t5, a1, a1      # E : chchchchchchchch
  54         xor     t0, a1, t1      # E : make bytes == c zero
  55         cmpbge  zero, t1, t3    # E : bits set iff byte == c
  56         or      t2, t3, t0      # E : bits set iff char match or zero match
  57 
  58         andnot  t0, t4, t0      # E : clear garbage bits
  59         cttz    t0, a2          # U0 : speculative (in case we get a match)
  60         nop                     # E :
  61         bne     t0, $found      # U :
  62 
  63         /*
  64          * Yuk.  This loop is going to stall like crazy waiting for the
  65          * data to be loaded.  Not much can be done about it unless it's
  66          * unrolled multiple times - is that safe to do in kernel space?
  67          * Or would exception handling recovery code do the trick here?
  68          */
  69 $loop:  ldq     t0, 8(v0)       # L : Latency=3
  70         addq    v0, 8, v0       # E :
  71         xor     t0, a1, t1      # E :
  72         cmpbge  zero, t0, t2    # E : bits set iff byte == 0
  73 
  74         cmpbge  zero, t1, t3    # E : bits set iff byte == c
  75         or      t2, t3, t0      # E :
  76         cttz    t3, a2          # U0 : speculative (in case we get a match)
  77         beq     t0, $loop       # U :
  78 
  79 $found: negq    t0, t1          # E : clear all but least set bit
  80         and     t0, t1, t0      # E :
  81         and     t0, t3, t1      # E : bit set iff byte was the char
  82         addq    v0, a2, v0      # E : Add in the bit number from above
  83 
  84         cmoveq  t1, $31, v0     # E : Two mapping slots, latency = 2
  85         nop
  86         nop
  87         ret                     # L0 :
  88 
  89         .end strchr
  90         EXPORT_SYMBOL(strchr)