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/*
 * arch/alpha/lib/ev67-strrchr.S
 * 21264 version by Rick Gorton <rick.gorton@alpha-processor.com>
 *
 * 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 <asm/regdef.h>

        .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