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path: root/src/string/armel/memcpy.s
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/*
 * Copyright (C) 2008 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */


/*
 * Optimized memcpy() for ARM.
 *
 * note that memcpy() always returns the destination pointer,
 * so we have to preserve R0.
  */

/*
 * This file has been modified from the original for use in musl libc.
 * The main changes are: addition of .type memcpy,%function to make the
 * code safely callable from thumb mode, adjusting the return
 * instructions to be compatible with pre-thumb ARM cpus, and removal
 * of prefetch code that is not compatible with older cpus.
 */

.global memcpy
.type memcpy,%function
memcpy:
	/* The stack must always be 64-bits aligned to be compliant with the
	 * ARM ABI. Since we have to save R0, we might as well save R4
	 * which we can use for better pipelining of the reads below
	 */
        .fnstart
        .save       {r0, r4, lr}
        stmfd       sp!, {r0, r4, lr}
        /* Making room for r5-r11 which will be spilled later */
        .pad        #28
        sub         sp, sp, #28

        /* it simplifies things to take care of len<4 early */
        cmp	r2, #4
        blo	copy_last_3_and_return

        /* compute the offset to align the source
         * offset = (4-(src&3))&3 = -src & 3
         */
        rsb	r3, r1, #0
        ands	r3, r3, #3
        beq	src_aligned

        /* align source to 32 bits. We need to insert 2 instructions between
         * a ldr[b|h] and str[b|h] because byte and half-word instructions
         * stall 2 cycles.
         */
        movs	r12, r3, lsl #31
        sub	r2, r2, r3		/* we know that r3 <= r2 because r2 >= 4 */
        .word 0x44d13001 /* ldrbmi r3, [r1], #1 */
        .word 0x24d14001 /* ldrbcs r4, [r1], #1 */
        .word 0x24d1c001 /* ldrbcs r12,[r1], #1 */
        .word 0x44c03001 /* strbmi r3, [r0], #1 */
        .word 0x24c04001 /* strbcs r4, [r0], #1 */
        .word 0x24c0c001 /* strbcs r12,[r0], #1 */

src_aligned:

	/* see if src and dst are aligned together (congruent) */
	eor	r12, r0, r1
        tst	r12, #3
        bne	non_congruent

        /* Use post-incriment mode for stm to spill r5-r11 to reserved stack
         * frame. Don't update sp.
         */
        stmea	sp, {r5-r11}

        /* align the destination to a cache-line */
        rsb	r3, r0, #0
        ands	r3, r3, #0x1C
        beq    	congruent_aligned32
        cmp    	r3, r2
        andhi	r3, r2, #0x1C

        /* conditionnaly copies 0 to 7 words (length in r3) */
        movs	r12, r3, lsl #28
        ldmcs	r1!, {r4, r5, r6, r7}		/* 16 bytes */
        ldmmi	r1!, {r8, r9}			/*  8 bytes */
        stmcs	r0!, {r4, r5, r6, r7}
        stmmi	r0!, {r8, r9}
        tst    	r3, #0x4
        ldrne	r10,[r1], #4			/*  4 bytes */
        strne	r10,[r0], #4
        sub    	r2, r2, r3

congruent_aligned32:
	/*
 	 * here source is aligned to 32 bytes.
 	 */

cached_aligned32:
        subs   	r2, r2, #32
        blo    	less_than_32_left

        /*
         * We preload a cache-line up to 64 bytes ahead. On the 926, this will
         * stall only until the requested world is fetched, but the linefill
         * continues in the the background.
         * While the linefill is going, we write our previous cache-line
         * into the write-buffer (which should have some free space).
         * When the linefill is done, the writebuffer will
         * start dumping its content into memory
         *
         * While all this is going, we then load a full cache line into
         * 8 registers, this cache line should be in the cache by now
         * (or partly in the cache).
         *
         * This code should work well regardless of the source/dest alignment.
         *
         */

        /* Align the preload register to a cache-line because the cpu does
         * "critical word first" (the first word requested is loaded first).
         */
        @ bic    	r12, r1, #0x1F
        @ add    	r12, r12, #64

1:      ldmia  	r1!, { r4-r11 }
        subs   	r2, r2, #32

        /* 
         * NOTE: if r12 is more than 64 ahead of r1, the following ldrhi
         * for ARM9 preload will not be safely guarded by the preceding subs.
         * When it is safely guarded the only possibility to have SIGSEGV here
         * is because the caller overstates the length.
         */
        @ ldrhi  	r3, [r12], #32      /* cheap ARM9 preload */
        stmia  	r0!, { r4-r11 }
	bhs    	1b

        add	r2, r2, #32

less_than_32_left:
	/*
	 * less than 32 bytes left at this point (length in r2)
	 */

	/* skip all this if there is nothing to do, which should
	 * be a common case (if not executed the code below takes
	 * about 16 cycles)
	 */
	tst	r2, #0x1F
        beq	1f

        /* conditionnaly copies 0 to 31 bytes */
        movs	r12, r2, lsl #28
        ldmcs	r1!, {r4, r5, r6, r7}		/* 16 bytes */
        ldmmi	r1!, {r8, r9}			/*  8 bytes */
        stmcs	r0!, {r4, r5, r6, r7}
        stmmi	r0!, {r8, r9}
        movs	r12, r2, lsl #30
        ldrcs	r3, [r1], #4			/*  4 bytes */
        .word 0x40d140b2 /* ldrhmi r4, [r1], #2 */ /*  2 bytes */
        strcs	r3, [r0], #4
        .word 0x40c040b2 /* strhmi r4, [r0], #2 */
        tst    	r2, #0x1
        .word 0x15d13000 /* ldrbne r3, [r1] */	/*  last byte  */
        .word 0x15c03000 /* strbne r3, [r0] */

        /* we're done! restore everything and return */
1:	ldmfd	sp!, {r5-r11}
        ldmfd	sp!, {r0, r4, lr}
        tst	lr, #1
        moveq	pc, lr
        bx	lr

	/********************************************************************/

non_congruent:
	/*
	 * here source is aligned to 4 bytes
	 * but destination is not.
	 *
	 * in the code below r2 is the number of bytes read
	 * (the number of bytes written is always smaller, because we have
	 * partial words in the shift queue)
	 */
	cmp	r2, #4
	blo	copy_last_3_and_return

        /* Use post-incriment mode for stm to spill r5-r11 to reserved stack
         * frame. Don't update sp.
         */
        stmea	sp, {r5-r11}

        /* compute shifts needed to align src to dest */
        rsb	r5, r0, #0
        and	r5, r5, #3			/* r5 = # bytes in partial words */
        mov	r12, r5, lsl #3		/* r12 = right */
        rsb	lr, r12, #32		/* lr = left  */

        /* read the first word */
        ldr	r3, [r1], #4
        sub	r2, r2, #4

        /* write a partial word (0 to 3 bytes), such that destination
         * becomes aligned to 32 bits (r5 = nb of words to copy for alignment)
         */
        movs	r5, r5, lsl #31
        .word 0x44c03001 /* strbmi r3, [r0], #1 */
        movmi	r3, r3, lsr #8
        .word 0x24c03001 /* strbcs r3, [r0], #1 */
        movcs	r3, r3, lsr #8
        .word 0x24c03001 /* strbcs r3, [r0], #1 */
        movcs	r3, r3, lsr #8

        cmp	r2, #4
        blo	partial_word_tail

        /* Align destination to 32 bytes (cache line boundary) */
1:	tst	r0, #0x1c
        beq	2f
        ldr	r5, [r1], #4
        sub    	r2, r2, #4
        orr	r4, r3, r5,		lsl lr
        mov	r3, r5,			lsr r12
        str	r4, [r0], #4
        cmp    	r2, #4
        bhs	1b
        blo	partial_word_tail

	/* copy 32 bytes at a time */
2:	subs	r2, r2, #32
	blo	less_than_thirtytwo

        /* Use immediate mode for the shifts, because there is an extra cycle
         * for register shifts, which could account for up to 50% of
         * performance hit.
         */

        cmp	r12, #24
        beq	loop24
        cmp	r12, #8
        beq	loop8

loop16:
        ldr    	r12, [r1], #4
1:      mov    	r4, r12
	ldmia	r1!, {   r5,r6,r7,  r8,r9,r10,r11}
        subs   	r2, r2, #32
        ldrhs  	r12, [r1], #4
	orr	r3, r3, r4, lsl #16
        mov	r4, r4, lsr #16
        orr	r4, r4, r5, lsl #16
        mov	r5, r5, lsr #16
        orr	r5, r5, r6, lsl #16
        mov	r6, r6, lsr #16
        orr	r6, r6, r7, lsl #16
        mov	r7, r7, lsr #16
        orr	r7, r7, r8, lsl #16
        mov	r8, r8, lsr #16
        orr	r8, r8, r9, lsl #16
        mov	r9, r9, lsr #16
        orr	r9, r9, r10, lsl #16
        mov	r10, r10,		lsr #16
        orr	r10, r10, r11, lsl #16
        stmia	r0!, {r3,r4,r5,r6, r7,r8,r9,r10}
        mov	r3, r11, lsr #16
        bhs	1b
        b	less_than_thirtytwo

loop8:
        ldr    	r12, [r1], #4
1:      mov    	r4, r12
	ldmia	r1!, {   r5,r6,r7,  r8,r9,r10,r11}
	subs	r2, r2, #32
        ldrhs  	r12, [r1], #4
        orr	r3, r3, r4, lsl #24
        mov	r4, r4, lsr #8
        orr	r4, r4, r5, lsl #24
        mov	r5, r5, lsr #8
        orr	r5, r5, r6, lsl #24
        mov	r6, r6,	 lsr #8
        orr	r6, r6, r7, lsl #24
        mov	r7, r7,	 lsr #8
        orr	r7, r7, r8,		lsl #24
        mov	r8, r8,	 lsr #8
        orr	r8, r8, r9,		lsl #24
        mov	r9, r9,	 lsr #8
        orr	r9, r9, r10,	lsl #24
        mov	r10, r10, lsr #8
        orr	r10, r10, r11,	lsl #24
        stmia	r0!, {r3,r4,r5,r6, r7,r8,r9,r10}
        mov	r3, r11, lsr #8
        bhs	1b
        b	less_than_thirtytwo

loop24:
        ldr    	r12, [r1], #4
1:      mov    	r4, r12
	ldmia	r1!, {   r5,r6,r7,  r8,r9,r10,r11}
        subs	r2, r2, #32
        ldrhs  	r12, [r1], #4
        orr	r3, r3, r4, lsl #8
        mov	r4, r4, lsr #24
        orr	r4, r4, r5, lsl #8
        mov	r5, r5, lsr #24
        orr	r5, r5, r6, lsl #8
        mov	r6, r6, lsr #24
        orr	r6, r6, r7, lsl #8
        mov	r7, r7, lsr #24
        orr	r7, r7, r8, lsl #8
        mov	r8, r8, lsr #24
        orr	r8, r8, r9, lsl #8
        mov	r9, r9, lsr #24
        orr	r9, r9, r10, lsl #8
        mov	r10, r10, lsr #24
        orr	r10, r10, r11, lsl #8
        stmia	r0!, {r3,r4,r5,r6, r7,r8,r9,r10}
        mov	r3, r11, lsr #24
        bhs	1b

less_than_thirtytwo:
	/* copy the last 0 to 31 bytes of the source */
	rsb	r12, lr, #32		/* we corrupted r12, recompute it  */
        add	r2, r2, #32
        cmp	r2, #4
        blo	partial_word_tail

1:	ldr	r5, [r1], #4
        sub    	r2, r2, #4
        orr	r4, r3, r5,		lsl lr
        mov	r3,	r5,			lsr r12
        str	r4, [r0], #4
        cmp    	r2, #4
        bhs	1b

partial_word_tail:
	/* we have a partial word in the input buffer */
	movs	r5, lr, lsl #(31-3)
	.word 0x44c03001 /* strbmi r3, [r0], #1 */
        movmi	r3, r3, lsr #8
        .word 0x24c03001 /* strbcs r3, [r0], #1 */
        movcs	r3, r3, lsr #8
        .word 0x24c03001 /* strbcs r3, [r0], #1 */

        /* Refill spilled registers from the stack. Don't update sp. */
        ldmfd	sp, {r5-r11}

copy_last_3_and_return:
	movs	r2, r2, lsl #31	/* copy remaining 0, 1, 2 or 3 bytes */
        .word 0x44d12001 /* ldrbmi r2, [r1], #1 */
        .word 0x24d13001 /* ldrbcs r3, [r1], #1 */
        .word 0x25d1c000 /* ldrbcs r12,[r1] */
        .word 0x44c02001 /* strbmi r2, [r0], #1 */
        .word 0x24c03001 /* strbcs r3, [r0], #1 */
        .word 0x25c0c000 /* strbcs r12,[r0] */

        /* we're done! restore sp and spilled registers and return */
        add    	sp,  sp, #28
        ldmfd	sp!, {r0, r4, lr}
        tst	lr, #1
        moveq	pc, lr
        bx	lr