audk/MdePkg/Library/BaseMemoryLibOptDxe/Arm/ScanMem.asm

; Copyright (c) 2010-2011, Linaro Limited
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;
; Written by Dave Gilbert <david.gilbert@linaro.org>
;
; This memchr routine is optimised on a Cortex-A9 and should work on
; all ARMv7 processors.   It has a fast past for short sizes, and has
; an optimised path for large data sets; the worst case is finding the
; match early in a large data set.
;


; 2011-02-07 david.gilbert@linaro.org
;    Extracted from local git a5b438d861
; 2011-07-14 david.gilbert@linaro.org
;    Import endianness fix from local git ea786f1b
; 2011-12-07 david.gilbert@linaro.org
;    Removed unneeded cbz from align loop

; this lets us check a flag in a 00/ff byte easily in either endianness
#define CHARTSTMASK(c) 1<<(c*8)

    EXPORT  InternalMemScanMem8
    AREA    ScanMem, CODE, READONLY
    THUMB

InternalMemScanMem8
    ; r0 = start of memory to scan
    ; r1 = length
    ; r2 = character to look for
    ; returns r0 = pointer to character or NULL if not found
    uxtb    r2, r2        ; Don't think we can trust the caller to actually pass a char

    cmp     r1, #16       ; If it's short don't bother with anything clever
    blt     L20

    tst     r0, #7        ; If it's already aligned skip the next bit
    beq     L10

    ; Work up to an aligned point
L5
    ldrb    r3, [r0],#1
    subs    r1, r1, #1
    cmp     r3, r2
    beq     L50           ; If it matches exit found
    tst     r0, #7
    bne     L5            ; If not aligned yet then do next byte

L10
    ; At this point, we are aligned, we know we have at least 8 bytes to work with
    push    {r4-r7}
    orr     r2, r2, r2, lsl #8  ; expand the match word across to all bytes
    orr     r2, r2, r2, lsl #16
    bic     r4, r1, #7    ; Number of double words to work with
    mvns    r7, #0        ; all F's
    movs    r3, #0

L15
    ldmia   r0!, {r5,r6}
    subs    r4, r4, #8
    eor     r5, r5, r2    ; Get it so that r5,r6 have 00's where the bytes match the target
    eor     r6, r6, r2
    uadd8   r5, r5, r7    ; Parallel add 0xff - sets the GE bits for anything that wasn't 0
    sel     r5, r3, r7    ; bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
    uadd8   r6, r6, r7    ; Parallel add 0xff - sets the GE bits for anything that wasn't 0
    sel     r6, r5, r7    ; chained....bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
    cbnz    r6, L60
    bne     L15           ; (Flags from the subs above) If not run out of bytes then go around again

    pop     {r4-r7}
    and     r2, r2, #0xff ; Get r2 back to a single character from the expansion above
    and     r1, r1, #7    ; Leave the count remaining as the number after the double words have been done

L20
    cbz     r1, L40       ; 0 length or hit the end already then not found

L21 ; Post aligned section, or just a short call
    ldrb    r3, [r0], #1
    subs    r1, r1, #1
    eor     r3, r3, r2    ; r3 = 0 if match - doesn't break flags from sub
    cbz     r3, L50
    bne     L21           ; on r1 flags

L40
    movs    r0, #0        ; not found
    bx      lr

L50
    subs    r0, r0, #1    ; found
    bx      lr

L60 ; We're here because the fast path found a hit - now we have to track down exactly which word it was
    ; r0 points to the start of the double word after the one that was tested
    ; r5 has the 00/ff pattern for the first word, r6 has the chained value
    cmp     r5, #0
    itte    eq
    moveq   r5, r6        ; the end is in the 2nd word
    subeq   r0, r0, #3    ; Points to 2nd byte of 2nd word
    subne   r0, r0, #7    ; or 2nd byte of 1st word

    ; r0 currently points to the 3rd byte of the word containing the hit
    tst     r5, #CHARTSTMASK(0)     ; 1st character
    bne     L61
    adds    r0, r0, #1
    tst     r5, #CHARTSTMASK(1)     ; 2nd character
    ittt    eq
    addeq   r0, r0 ,#1
    tsteq   r5, #(3 << 15)          ; 2nd & 3rd character
    ; If not the 3rd must be the last one
    addeq   r0, r0, #1

L61
    pop     {r4-r7}
    subs    r0, r0, #1
    bx      lr

    END