Subversion Repositories or1k_soc_on_altera_embedded_dev_kit

/*

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

 * 21264 version contributed by Rick Gorton 

 *

 * 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 

        .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