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/*
 * arch/alpha/lib/ev6-memchr.S
 *
 * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com>
 *
 * Finds characters in a memory area.  Optimized for the Alpha:
 *
 *    - memory accessed as aligned quadwords only
 *    - uses cmpbge to compare 8 bytes in parallel
 *    - does binary search to find 0 byte in last
 *      quadword (HAKMEM needed 12 instructions to
 *      do this instead of the 9 instructions that
 *      binary search needs).
 *
 * For correctness consider that:
 *
 *    - only minimum number of quadwords may be accessed
 *    - the third argument is an unsigned long
 *
 * 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
 * Try not to change the actual algorithm if possible for consistency.
 */

        .set noreorder
        .set noat

        .align  4
        .globl memchr
        .ent memchr
memchr:
        .frame $30,0,$26,0
        .prologue 0

        # Hack -- if someone passes in (size_t)-1, hoping to just
        # search til the end of the address space, we will overflow
        # below when we find the address of the last byte.  Given
        # that we will never have a 56-bit address space, cropping
        # the length is the easiest way to avoid trouble.
        zap     $18, 0x80, $5   # U : Bound length
        beq     $18, $not_found # U :
        ldq_u   $1, 0($16)      # L : load first quadword Latency=3
        and     $17, 0xff, $17  # E : L L U U : 00000000000000ch

        insbl   $17, 1, $2      # U : 000000000000ch00
        cmpult  $18, 9, $4      # E : small (< 1 quad) string?
        or      $2, $17, $17    # E : 000000000000chch
        lda     $3, -1($31)     # E : U L L U

        sll     $17, 16, $2     # U : 00000000chch0000
        addq    $16, $5, $5     # E : Max search address
        or      $2, $17, $17    # E : 00000000chchchch
        sll     $17, 32, $2     # U : U L L U : chchchch00000000

        or      $2, $17, $17    # E : chchchchchchchch
        extql   $1, $16, $7     # U : $7 is upper bits
        beq     $4, $first_quad # U :
        ldq_u   $6, -1($5)      # L : L U U L : eight or less bytes to search Latency=3

        extqh   $6, $16, $6     # U : 2 cycle stall for $6
        mov     $16, $0         # E :
        nop                     # E :
        or      $7, $6, $1      # E : L U L U $1 = quadword starting at $16

        # Deal with the case where at most 8 bytes remain to be searched
        # in $1.  E.g.:
        #       $18 = 6
        #       $1 = ????c6c5c4c3c2c1
$last_quad:
        negq    $18, $6         # E :
        xor     $17, $1, $1     # E :
        srl     $3, $6, $6      # U : $6 = mask of $18 bits set
        cmpbge  $31, $1, $2     # E : L U L U

        nop
        nop
        and     $2, $6, $2      # E :
        beq     $2, $not_found  # U : U L U L

$found_it:
#if defined(__alpha_fix__) && defined(__alpha_cix__)
        /*
         * Since we are guaranteed to have set one of the bits, we don't
         * have to worry about coming back with a 0x40 out of cttz...
         */
        cttz    $2, $3          # U0 :
        addq    $0, $3, $0      # E : All done
        nop                     # E :
        ret                     # L0 : L U L U
#else
        /*
         * Slow and clunky.  It can probably be improved.
         * An exercise left for others.
         */
        negq    $2, $3          # E :
        and     $2, $3, $2      # E :
        and     $2, 0x0f, $1    # E :
        addq    $0, 4, $3       # E :

        cmoveq  $1, $3, $0      # E : Latency 2, extra map cycle
        nop                     # E : keep with cmov
        and     $2, 0x33, $1    # E :
        addq    $0, 2, $3       # E : U L U L : 2 cycle stall on $0

        cmoveq  $1, $3, $0      # E : Latency 2, extra map cycle
        nop                     # E : keep with cmov
        and     $2, 0x55, $1    # E :
        addq    $0, 1, $3       # E : U L U L : 2 cycle stall on $0

        cmoveq  $1, $3, $0      # E : Latency 2, extra map cycle
        nop
        nop
        ret                     # L0 : L U L U
#endif

        # Deal with the case where $18 > 8 bytes remain to be
        # searched.  $16 may not be aligned.
        .align 4
$first_quad:
        andnot  $16, 0x7, $0    # E :
        insqh   $3, $16, $2     # U : $2 = 0000ffffffffffff ($16<0:2> ff)
        xor     $1, $17, $1     # E :
        or      $1, $2, $1      # E : U L U L $1 = ====ffffffffffff

        cmpbge  $31, $1, $2     # E :
        bne     $2, $found_it   # U :
        # At least one byte left to process.
        ldq     $1, 8($0)       # L :
        subq    $5, 1, $18      # E : U L U L

        addq    $0, 8, $0       # E :
        # Make $18 point to last quad to be accessed (the
        # last quad may or may not be partial).
        andnot  $18, 0x7, $18   # E :
        cmpult  $0, $18, $2     # E :
        beq     $2, $final      # U : U L U L

        # At least two quads remain to be accessed.

        subq    $18, $0, $4     # E : $4 <- nr quads to be processed
        and     $4, 8, $4       # E : odd number of quads?
        bne     $4, $odd_quad_count # U :
        # At least three quads remain to be accessed
        mov     $1, $4          # E : L U L U : move prefetched value to correct reg

        .align  4
$unrolled_loop:
        ldq     $1, 8($0)       # L : prefetch $1
        xor     $17, $4, $2     # E :
        cmpbge  $31, $2, $2     # E :
        bne     $2, $found_it   # U : U L U L

        addq    $0, 8, $0       # E :
        nop                     # E :
        nop                     # E :
        nop                     # E :

$odd_quad_count:
        xor     $17, $1, $2     # E :
        ldq     $4, 8($0)       # L : prefetch $4
        cmpbge  $31, $2, $2     # E :
        addq    $0, 8, $6       # E :

        bne     $2, $found_it   # U :
        cmpult  $6, $18, $6     # E :
        addq    $0, 8, $0       # E :
        nop                     # E :

        bne     $6, $unrolled_loop # U :
        mov     $4, $1          # E : move prefetched value into $1
        nop                     # E :
        nop                     # E :

$final: subq    $5, $0, $18     # E : $18 <- number of bytes left to do
        nop                     # E :
        nop                     # E :
        bne     $18, $last_quad # U :

$not_found:
        mov     $31, $0         # E :
        nop                     # E :
        nop                     # E :
        ret                     # L0 :

        .end memchr