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/*

 * arch/alpha/lib/ev67-strrchr.S

 * 21264 version by Rick Gorton 

 *

 * Finds length of a 0-terminated string.  Optimized for the

 * Alpha architecture:

 *

 *      - memory accessed as aligned quadwords only

 *      - uses bcmpge to compare 8 bytes in parallel

 *

 * Much of the information about 21264 scheduling/coding comes from:

 *      Compiler Writer's Guide for the Alpha 21264

 *      abbreviated as 'CWG' in other comments here

 *      ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html

 * Scheduling notation:

 *      E       - either cluster

 *      U       - upper subcluster; U0 - subcluster U0; U1 - subcluster U1

 *      L       - lower subcluster; L0 - subcluster L0; L1 - subcluster L1

 */

#include 

        .set noreorder

        .set noat

        .align 4

        .ent strrchr

        .globl strrchr

strrchr:

        .frame sp, 0, ra

        .prologue 0

        and     a1, 0xff, t2    # E : 00000000000000ch

        insbl   a1, 1, t4       # U : 000000000000ch00

        insbl   a1, 2, t5       # U : 0000000000ch0000

        ldq_u   t0, 0(a0)       # L : load first quadword Latency=3

        mov     zero, t6        # E : t6 is last match aligned addr

        or      t2, t4, a1      # E : 000000000000chch

        sll     t5, 8, t3       # U : 00000000ch000000

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

        andnot  a0, 7, v0       # E : align source addr

        or      t5, t3, t3      # E : 00000000chch0000

        sll     a1, 32, t2      # U : 0000chch00000000

        sll     a1, 48, t4      # U : chch000000000000

        or      t4, a1, a1      # E : chch00000000chch

        or      t2, t3, t2      # E : 0000chchchch0000

        or      a1, t2, a1      # E : chchchchchchchch

        lda     t5, -1          # E : build garbage mask

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

        mskqh   t5, a0, t4      # E : Complete garbage mask

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

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

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

        andnot  t1, t4, t1      # E : clear garbage from null test

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

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

        /* Character search main loop */

$loop:

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

        cmovne  t3, v0, t6      # E : save previous comparisons match

        nop                     #   : Latency=2, extra map slot (keep nop with cmov)

        nop

        cmovne  t3, t3, t8      # E : Latency=2, extra map slot

        nop                     #   : keep with cmovne

        addq    v0, 8, v0       # E :

        xor     t0, a1, t2      # E :

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

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

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

        nop

        /* Mask out character matches after terminator */

$eos:

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

        and     t1, t4, t4      # E :

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

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

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

        cmovne  t3, t3, t8      # E : save it, if match found Latency=2, extra map slot

        nop                     #   : Keep with cmovne

        nop

        cmovne  t3, v0, t6      # E :

        nop                     #   : Keep with cmovne

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

        ctlz    t8, t2          # U0 : Latency=3 (0x40 for t8=0)

        nop

        cmoveq  t8, 0x3f, t2    # E : Compensate for case when no match is seen

        nop                     # E : hide the cmov latency (2) behind ctlz latency

        lda     t5, 0x3f($31)   # E :

        subq    t5, t2, t5      # E : Normalize leading zero count

        addq    t6, t5, v0      # E : and add to quadword address

        ret                     # L0 : Latency=3

        nop

        nop

        .end strrchr