Subversion Repositories HelenOS

    .align 2

different_aligns:

    /* We must do byte copies */

    stmfd r13!, {r0, lr }

byte_loop:

    ldrb r3, [r1], #1

    strb r3, [r0], #1

    subs r2, r2, #1

    bne byte_loop

    ldmfd r13!, {r0, pc }

        .type memcpy, %function

memcpy:

@void* memcpy( void* dst, const void* src, size_t len )

@@ Register usage:

@@ r0: dst

@@ r1: src

@@

@@ r3: various bitmasks, load and store for different_aligns loop

@@ r4: counter for multi loop, not used for different_aligns

@@ r5-r8: load and store, not used for different_aligns

    /*check for src alignment*/

    eor r3, r0, r1 @ r3 = dest | src

    tst r3, #3 @ test for same alignment

    bne different_aligns @ jump if align( r1 ) != align( ro )

    /* else, they have the same same alignment */

    stmfd r13!, {r0, r4-r8, lr } @ save regs

    ands r3, r0, #3 @ find out what that alignment is

    beq multi @ iff align( r1 ) == align( r0 ) == 0 skip to multi

    /* otherwise, move up to three bytes to get to a word alignment

       if align = 1, we need to move forward 3 bytes to get to a word boundry

       if align = 2, we need to move forward 2 bytes to get to a word boundry

       if align = 3, we need to move forward 1 byte to get to a word boundry

    */

    cmp r3, #2 @ "subtract" 2 from either 1, 2, or 3

    ldrneb r4, [r1], #1 @ one aligned or three aligned ( 1 != 2 || 3 !- 2 ), ((byte*) src)++

    strneb r4, [r0], #1 @ one aligned or three aligned ( 1 != 2 || 3 !- 2 ), store to *dst++

    @ldrlsh r4, [r1], #2 @ one or two ( 1 <= 2 || 2 <= 2 ) aligned, ((halfword*) src)++

    @strlsh r4, [r0], #2 @ one or two ( 1 <= 2 || 2 <= 2 ) aligned, store to *dst++

    ldrlsb r4, [r1], #1 @ one aligned or two aligned, ((byte*) src)++

    strlsb r4, [r0], #1 @ one aligned or two aligned, store to *dst++

    ldrlsb r4, [r1], #1 @ one aligned or two aligned, ((byte*) src)++

    strlsb r4, [r0], #1 @ one aligned or two aligned, store to *dst++

    sub r3, r3, #4

    add r2, r2, r3 @ length -= bytes written

multi:

    /* once we get here, we're word aligned */

    /*

    bytes = length

    words = byte / 4, rem = byte moves

    instr = quadword = words / 4, rem = partial instructions

    loop = instr / 4, rem = jump to instr

    010101010

    llliiwwbb

    21

    52631

    684268421

    */

    ands r3, r2, #48 @ #32 | #16, r3 = partial loop count << 3

    mov r4, r2, LSR #6 @ r4 = loop count

    /* Now, like Duff's device, jump into the loop to perform the extra instructions */

    /* Replace later with direct adjustment of PC */

    beq loop_test

    cmp r3, #32 @r3 = 16 or 32 or 48, corresponding to 1 or 2 or 3

    bhi loop3

    beq loop2

    blo loop1

loop:

    ldmia r1!, { r5-r8 } @load four registers

    stmia r0!, { r5-r8 } @store four registers

loop3:

    ldmia r1!, { r5-r8 } @load four registers

    stmia r0!, { r5-r8 } @store four registers

loop2:

    ldmia r1!, { r5-r8 } @load four registers

    stmia r0!, { r5-r8 } @store four registers

loop1:

    ldmia r1!, { r5-r8 } @load four registers

    stmia r0!, { r5-r8 } @store four registers

loop_test:

    cmp r4, #0

    subne r4, r4, #1

    bne loop

    /* Now do the extra words */

    ands r3, r2, #12 @ #8 | #4, r3 = extra words << 2

    beq extra_bytes

    cmp r3, #8

    ldrne r5, [r1], #4 @ if r5 !=8 then it's 4 or 12, so load and store

    strne r5, [r0], #4

    ldmhsia r1!, {r5-r6} @ if r5 >= 8, it's 8 or 12, so load and store 2

    stmhsia r0!, {r5-r6}

    /* Now do the extra bytes */

extra_bytes:

    tst r2, #2 @ any extra bytes?

    beq clean_up

    cmp r3, #2 @ subtract 2 from either 1, 2, or 3

    ldrneb r5, [r1], #1 @ load and store one byte iff r3 != 2 (i.e, r3 == 1 || r3 == 3)

    strneb r5, [r0], #1 @ 1 or 3

    ldrhsb r5, [r1], #1 @ load and store a byte iff r3 >= 2

    strhsb r5, [r0], #1 @ 2 or 3

    ldrhsb r5, [r1], #1 @ load and store a byte iff r3 > 2

    strhsb r5, [r0], #1 @ 2 or 3

clean_up:

    ldmfd r13!, {r0, r4-r8, pc } @r0 is the retval, must equal original dst

end:

    .size different_aligns, .end-memcpy

        .align 2

@ Local Variables:

@ asm-comment-char: ?@

@ comment-start: "@ "

@ block-comment-start: "/*"

@ block-comment-end: "*/"

@ indent-tabs-mode: t

@ End: