/* SPDX-License-Identifier: GPL-2.0 */
/*
 * arch/alpha/lib/ev67-strchr.S
 * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com>
 *
 * Return the address of a given character within a null-terminated
 * string, or null if it is not found.
 *
 * 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.
 */
#include <linux/export.h>
#include <asm/regdef.h>

        .set noreorder
        .set noat

        .align 4
        .globl strchr
        .ent strchr
strchr:
        .frame sp, 0, ra
        .prologue 0

        ldq_u   t0, 0(a0)       # L : load first quadword Latency=3
        and     a1, 0xff, t3    # E : 00000000000000ch
        insbl   a1, 1, t5       # U : 000000000000ch00
        insbl   a1, 7, a2       # U : ch00000000000000

        insbl   t3, 6, a3       # U : 00ch000000000000
        or      t5, t3, a1      # E : 000000000000chch
        andnot  a0, 7, v0       # E : align our loop pointer
        lda     t4, -1          # E : build garbage mask

        mskqh   t4, a0, t4      # U : only want relevant part of first quad
        or      a2, a3, a2      # E : chch000000000000
        inswl   a1, 2, t5       # E : 00000000chch0000
        inswl   a1, 4, a3       # E : 0000chch00000000

        or      a1, a2, a1      # E : chch00000000chch
        or      a3, t5, t5      # E : 0000chchchch0000
        cmpbge  zero, t0, t2    # E : bits set iff byte == zero
        cmpbge  zero, t4, t4    # E : bits set iff byte is garbage

        /* This quad is _very_ serialized.  Lots of stalling happens */
        or      t5, a1, a1      # E : chchchchchchchch
        xor     t0, a1, t1      # E : make bytes == c zero
        cmpbge  zero, t1, t3    # E : bits set iff byte == c
        or      t2, t3, t0      # E : bits set iff char match or zero match

        andnot  t0, t4, t0      # E : clear garbage bits
        cttz    t0, a2          # U0 : speculative (in case we get a match)
        nop                     # E :
        bne     t0, $found      # U :

        /*
         * Yuk.  This loop is going to stall like crazy waiting for the
         * data to be loaded.  Not much can be done about it unless it's
         * unrolled multiple times - is that safe to do in kernel space?
         * Or would exception handling recovery code do the trick here?
         */
$loop:  ldq     t0, 8(v0)       # L : Latency=3
        addq    v0, 8, v0       # E :
        xor     t0, a1, t1      # E :
        cmpbge  zero, t0, t2    # E : bits set iff byte == 0

        cmpbge  zero, t1, t3    # E : bits set iff byte == c
        or      t2, t3, t0      # E :
        cttz    t3, a2          # U0 : speculative (in case we get a match)
        beq     t0, $loop       # U :

$found: negq    t0, t1          # E : clear all but least set bit
        and     t0, t1, t0      # E :
        and     t0, t3, t1      # E : bit set iff byte was the char
        addq    v0, a2, v0      # E : Add in the bit number from above

        cmoveq  t1, $31, v0     # E : Two mapping slots, latency = 2
        nop
        nop
        ret                     # L0 :

        .end strchr
        EXPORT_SYMBOL(strchr)