path: root/src/string/armel/memcpy.s

/*
 * 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.
 */

.syntax unified

.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 */
	ldrbmi r3, [r1], #1
	ldrbcs r4, [r1], #1
	ldrbcs r12,[r1], #1
	strbmi r3, [r0], #1
	strbcs r4, [r0], #1
	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 */
	ldrhmi r4, [r1], #2                     /*  2 bytes */
	strcs   r3, [r0], #4
	strhmi r4, [r0], #2
	tst     r2, #0x1
	ldrbne r3, [r1]                         /*  last byte  */
	strbne r3, [r0]

	/* we're done! restore everything and return */
1:      ldmfd   sp!, {r5-r11}
	ldmfd   sp!, {r0, r4, 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
	strbmi r3, [r0], #1
	movmi   r3, r3, lsr #8
	strbcs r3, [r0], #1
	movcs   r3, r3, lsr #8
	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)
	strbmi r3, [r0], #1
	movmi   r3, r3, lsr #8
	strbcs r3, [r0], #1
	movcs   r3, r3, lsr #8
	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 */
	ldrbmi r2, [r1], #1
	ldrbcs r3, [r1], #1
	ldrbcs r12,[r1]
	strbmi r2, [r0], #1
	strbcs r3, [r0], #1
	strbcs r12,[r0]

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