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#
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#
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# Copyright (c) 2006 Martin Decky
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# Copyright (c) 2007 Michal Kebrt
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# All rights reserved.
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# All rights reserved.
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#
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#
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# Redistribution and use in source and binary forms, with or without
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# Redistribution and use in source and binary forms, with or without
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# modification, are permitted provided that the following conditions
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# modification, are permitted provided that the following conditions
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# are met:
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# are met:
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#
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#
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.text
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.text
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    .align 2
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.global memcpy
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- 
 
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- 
 
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different_aligns:
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    /* We must do byte copies */
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    stmfd r13!, {r0, lr }
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byte_loop:
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    ldrb r3, [r1], #1
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    strb r3, [r0], #1
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    subs r2, r2, #1
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    bne byte_loop
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    ldmfd r13!, {r0, pc }
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        .global memcpy
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        .type memcpy, %function
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memcpy:
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memcpy:
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@void* memcpy( void* dst, const void* src, size_t len )
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@@ Register usage:
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add     r3, r1, #3
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@@ r0: dst
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@@ r1: src
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@@ r2: len
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@@
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@@ r3: various bitmasks, load and store for different_aligns loop
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@@ r4: counter for multi loop, not used for different_aligns
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@@ r5-r8: load and store, not used for different_aligns
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    cmp r2, #0
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bic     r3, r3, #3
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    moveq pc, lr @ just return if caller wants to copy zero bytes
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    cmp r2, #8
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cmp     r1, r3
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    bls different_aligns
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stmdb   sp!, {r4, lr}
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    /*check for src alignment*/
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    eor r3, r0, r1 @ r3 = dest | src
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    tst r3, #3 @ test for same alignment
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    bne different_aligns @ jump if align( r1 ) != align( ro )
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    /* else, they have the same same alignment */
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    stmfd r13!, {r0, r4-r8, lr } @ save regs
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    ands r3, r0, #3 @ find out what that alignment is
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    beq multi @ iff align( r1 ) == align( r0 ) == 0 skip to multi
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beq     case_4
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    /* otherwise, move up to three bytes to get to a word alignment
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       if align = 1, we need to move forward 3 bytes to get to a word boundry
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       if align = 2, we need to move forward 2 bytes to get to a word boundry
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       if align = 3, we need to move forward 1 byte to get to a word boundry
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    */
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case_1:
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    cmp r3, #2 @ "subtract" 2 from either 1, 2, or 3
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    ldrneb r4, [r1], #1 @ one aligned or three aligned ( 1 != 2 || 3 !- 2 ), ((byte*) src)++
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    strneb r4, [r0], #1 @ one aligned or three aligned ( 1 != 2 || 3 !- 2 ), store to *dst++
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    @ldrlsh r4, [r1], #2 @ one or two ( 1 <= 2 || 2 <= 2 ) aligned, ((halfword*) src)++
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    @strlsh r4, [r0], #2 @ one or two ( 1 <= 2 || 2 <= 2 ) aligned, store to *dst++
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    ldrlsb r4, [r1], #1 @ one aligned or two aligned, ((byte*) src)++
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    strlsb r4, [r0], #1 @ one aligned or two aligned, store to *dst++
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    ldrlsb r4, [r1], #1 @ one aligned or two aligned, ((byte*) src)++
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    strlsb r4, [r0], #1 @ one aligned or two aligned, store to *dst++
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    sub r3, r3, #4
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cmp     r2, #0
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    add r2, r2, r3 @ length -= bytes written
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multi:
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movne   ip, #0
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    /* once we get here, we're word aligned */
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beq     case_3
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    /*
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case_2:
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    bytes = length
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ldrb    r3, [ip, r1]
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    words = byte / 4, rem = byte moves
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strb    r3, [ip, r0]
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    instr = quadword = words / 4, rem = partial instructions
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    loop = instr / 4, rem = jump to instr
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    010101010
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add     ip, ip, #1
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    llliiwwbb
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cmp     ip, r2
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bne     case_2
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    21
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case_3:
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    52631
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mov     r0, r1
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    684268421
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ldmia   sp!, {r4, pc}
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    */
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case_4:
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    ands r3, r2, #48 @ #32 | #16, r3 = partial loop count << 3
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add     r3, r0, #3
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    mov r4, r2, LSR #6 @ r4 = loop count
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bic     r3, r3, #3
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cmp     r0, r3
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    /* Now, like Duff's device, jump into the loop to perform the extra instructions */
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    /* Replace later with direct adjustment of PC */
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    beq loop_test
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bne     case_1
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    cmp r3, #32 @r3 = 16 or 32 or 48, corresponding to 1 or 2 or 3
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    bhi loop3
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movs    r4, r2, lsr #2
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    beq loop2
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moveq   lr, r4
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    blo loop1
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beq     case_6
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mov     lr, #0
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loop:
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    ldmia r1!, { r5-r8 } @load four registers
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    stmia r0!, { r5-r8 } @store four registers
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loop3:
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mov     ip, lr
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    ldmia r1!, { r5-r8 } @load four registers
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    stmia r0!, { r5-r8 } @store four registers
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loop2:
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case_5:
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    ldmia r1!, { r5-r8 } @load four registers
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ldr     r3, [ip, r1]
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    stmia r0!, { r5-r8 } @store four registers
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loop1:
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    ldmia r1!, { r5-r8 } @load four registers
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add     lr, lr, #1
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    stmia r0!, { r5-r8 } @store four registers
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cmp     lr, r4
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loop_test:
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    cmp r4, #0
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str     r3, [ip, r0]
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    subne r4, r4, #1
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add     ip, ip, #4
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    bne loop
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bne     case_5
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case_6:
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    /* Now do the extra words */
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ands    r4, r2, #3
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    ands r3, r2, #12 @ #8 | #4, r3 = extra words << 2
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    beq extra_bytes
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beq     case_3
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    cmp r3, #8
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mov     r3, lr, lsl #2
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    ldrne r5, [r1], #4 @ if r5 !=8 then it's 4 or 12, so load and store
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    strne r5, [r0], #4
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add     r0, r3, r0
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    ldmhsia r1!, {r5-r6} @ if r5 >= 8, it's 8 or 12, so load and store 2
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    stmhsia r0!, {r5-r6}
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add     ip, r3, r1
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mov     r2, #0
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    /* Now do the extra bytes */
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extra_bytes:
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case_7:
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    tst r2, #2 @ any extra bytes?
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    beq clean_up
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ldrb    r3, [r2, ip]
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    cmp r3, #2 @ subtract 2 from either 1, 2, or 3
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    ldrneb r5, [r1], #1 @ load and store one byte iff r3 != 2 (i.e, r3 == 1 || r3 == 3)
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    strneb r5, [r0], #1 @ 1 or 3
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strb    r3, [r2, r0]
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    ldrhsb r5, [r1], #1 @ load and store a byte iff r3 >= 2
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    strhsb r5, [r0], #1 @ 2 or 3
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add     r2, r2, #1
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    ldrhsb r5, [r1], #1 @ load and store a byte iff r3 > 2
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    strhsb r5, [r0], #1 @ 2 or 3
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cmp     r2, r4
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bne     case_7
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clean_up:
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b       case_3
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    ldmfd r13!, {r0, r4-r8, pc } @r0 is the retval, must equal original dst
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end:
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    .size different_aligns, .end-memcpy
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        .align 2
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@ Local Variables:
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@ asm-comment-char: ?@
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@ comment-start: "@ "
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@ block-comment-start: "/*"
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@ block-comment-end: "*/"
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@ indent-tabs-mode: t
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@ End:
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