LXR linux/arch/alpha/lib/strrchr.S

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