root/arch/alpha/lib/strrchr.S

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * arch/alpha/lib/strrchr.S
   4  * Contributed by Richard Henderson (rth@tamu.edu)
   5  *
   6  * Return the address of the last occurrence of a given character
   7  * within a null-terminated string, or null if it is not found.
   8  */
   9 #include <asm/export.h>
  10 #include <asm/regdef.h>
  11 
  12         .set noreorder
  13         .set noat
  14 
  15         .align 3
  16         .ent strrchr
  17         .globl strrchr
  18 strrchr:
  19         .frame sp, 0, ra
  20         .prologue 0
  21 
  22         zapnot  a1, 1, a1       # e0    : zero extend our test character
  23         mov     zero, t6        # .. e1 : t6 is last match aligned addr
  24         sll     a1, 8, t5       # e0    : replicate our test character
  25         mov     zero, t8        # .. e1 : t8 is last match byte compare mask
  26         or      t5, a1, a1      # e0    :
  27         ldq_u   t0, 0(a0)       # .. e1 : load first quadword
  28         sll     a1, 16, t5      # e0    :
  29         andnot  a0, 7, v0       # .. e1 : align source addr
  30         or      t5, a1, a1      # e0    :
  31         lda     t4, -1          # .. e1 : build garbage mask
  32         sll     a1, 32, t5      # e0    :
  33         cmpbge  zero, t0, t1    # .. e1 : bits set iff byte == zero
  34         mskqh   t4, a0, t4      # e0    :
  35         or      t5, a1, a1      # .. e1 : character replication complete
  36         xor     t0, a1, t2      # e0    : make bytes == c zero
  37         cmpbge  zero, t4, t4    # .. e1 : bits set iff byte is garbage
  38         cmpbge  zero, t2, t3    # e0    : bits set iff byte == c
  39         andnot  t1, t4, t1      # .. e1 : clear garbage from null test
  40         andnot  t3, t4, t3      # e0    : clear garbage from char test
  41         bne     t1, $eos        # .. e1 : did we already hit the terminator?
  42 
  43         /* Character search main loop */
  44 $loop:
  45         ldq     t0, 8(v0)       # e0    : load next quadword
  46         cmovne  t3, v0, t6      # .. e1 : save previous comparisons match
  47         cmovne  t3, t3, t8      # e0    :
  48         addq    v0, 8, v0       # .. e1 :
  49         xor     t0, a1, t2      # e0    :
  50         cmpbge  zero, t0, t1    # .. e1 : bits set iff byte == zero
  51         cmpbge  zero, t2, t3    # e0    : bits set iff byte == c
  52         beq     t1, $loop       # .. e1 : if we havnt seen a null, loop
  53 
  54         /* Mask out character matches after terminator */
  55 $eos:
  56         negq    t1, t4          # e0    : isolate first null byte match
  57         and     t1, t4, t4      # e1    :
  58         subq    t4, 1, t5       # e0    : build a mask of the bytes up to...
  59         or      t4, t5, t4      # e1    : ... and including the null
  60 
  61         and     t3, t4, t3      # e0    : mask out char matches after null
  62         cmovne  t3, t3, t8      # .. e1 : save it, if match found
  63         cmovne  t3, v0, t6      # e0    :
  64 
  65         /* Locate the address of the last matched character */
  66 
  67         /* Retain the early exit for the ev4 -- the ev5 mispredict penalty
  68            is 5 cycles -- the same as just falling through.  */
  69         beq     t8, $retnull    # .. e1 :
  70 
  71         and     t8, 0xf0, t2    # e0    : binary search for the high bit set
  72         cmovne  t2, t2, t8      # .. e1 (zdb)
  73         cmovne  t2, 4, t2       # e0    :
  74         and     t8, 0xcc, t1    # .. e1 :
  75         cmovne  t1, t1, t8      # e0    :
  76         cmovne  t1, 2, t1       # .. e1 :
  77         and     t8, 0xaa, t0    # e0    :
  78         cmovne  t0, 1, t0       # .. e1 (zdb)
  79         addq    t2, t1, t1      # e0    :
  80         addq    t6, t0, v0      # .. e1 : add our aligned base ptr to the mix
  81         addq    v0, t1, v0      # e0    :
  82         ret                     # .. e1 :
  83 
  84 $retnull:
  85         mov     zero, v0        # e0    :
  86         ret                     # .. e1 :
  87 
  88         .end strrchr
  89         EXPORT_SYMBOL(strrchr)