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/*

 * arch/alpha/lib/strrchr.S

 * Contributed by Richard Henderson (rth@tamu.edu)

 *

 * Return the address of the last occurrance of a given character

 * within a null-terminated string, or null if it is not found.

 */

#include 

        .set noreorder

        .set noat

        .align 3

        .ent strrchr

        .globl strrchr

strrchr:

        .frame sp, 0, ra

        .prologue 0

        zapnot  a1, 1, a1       # e0    : zero extend our test character

        mov     zero, t6        # .. e1 : t6 is last match aligned addr

        sll     a1, 8, t5       # e0    : replicate our test character

        mov     zero, t8        # .. e1 : t8 is last match byte compare mask

        or      t5, a1, a1      # e0    :

        ldq_u   t0, 0(a0)       # .. e1 : load first quadword

        sll     a1, 16, t5      # e0    :

        andnot  a0, 7, v0       # .. e1 : align source addr

        or      t5, a1, a1      # e0    :

        lda     t4, -1          # .. e1 : build garbage mask

        sll     a1, 32, t5      # e0    :

        cmpbge  zero, t0, t1    # .. e1 : bits set iff byte == zero

        mskqh   t4, a0, t4      # e0    :

        or      t5, a1, a1      # .. e1 : character replication complete

        xor     t0, a1, t2      # e0    : make bytes == c zero

        cmpbge  zero, t4, t4    # .. e1 : bits set iff byte is garbage

        cmpbge  zero, t2, t3    # e0    : bits set iff byte == c

        andnot  t1, t4, t1      # .. e1 : clear garbage from null test

        andnot  t3, t4, t3      # e0    : clear garbage from char test

        bne     t1, $eos        # .. e1 : did we already hit the terminator?

        /* Character search main loop */

$loop:

        ldq     t0, 8(v0)       # e0    : load next quadword

        cmovne  t3, v0, t6      # .. e1 : save previous comparisons match

        cmovne  t3, t3, t8      # e0    :

        addq    v0, 8, v0       # .. e1 :

        xor     t0, a1, t2      # e0    :

        cmpbge  zero, t0, t1    # .. e1 : bits set iff byte == zero

        cmpbge  zero, t2, t3    # e0    : bits set iff byte == c

        beq     t1, $loop       # .. e1 : if we havnt seen a null, loop

        /* Mask out character matches after terminator */

$eos:

        negq    t1, t4          # e0    : isolate first null byte match

        and     t1, t4, t4      # e1    :

        subq    t4, 1, t5       # e0    : build a mask of the bytes upto...

        or      t4, t5, t4      # e1    : ... and including the null

        and     t3, t4, t3      # e0    : mask out char matches after null

        cmovne  t3, t3, t8      # .. e1 : save it, if match found

        cmovne  t3, v0, t6      # e0    :

        /* Locate the address of the last matched character */

        /* Retain the early exit for the ev4 -- the ev5 mispredict penalty

           is 5 cycles -- the same as just falling through.  */

        beq     t8, $retnull    # .. e1 :

        and     t8, 0xf0, t2    # e0    : binary search for the high bit set

        cmovne  t2, t2, t8      # .. e1 (zdb)

        cmovne  t2, 4, t2       # e0    :

        and     t8, 0xcc, t1    # .. e1 :

        cmovne  t1, t1, t8      # e0    :

        cmovne  t1, 2, t1       # .. e1 :

        and     t8, 0xaa, t0    # e0    :

        cmovne  t0, 1, t0       # .. e1 (zdb)

        addq    t2, t1, t1      # e0    :

        addq    t6, t0, v0      # .. e1 : add our aligned base ptr to the mix

        addq    v0, t1, v0      # e0    :

        ret                     # .. e1 :

$retnull:

        mov     zero, v0        # e0    :

        ret                     # .. e1 :

        .end strrchr