170 lines
4.4 KiB
ArmAsm
170 lines
4.4 KiB
ArmAsm
/*
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* Copyright (c) 2008 Travis Geiselbrecht
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files
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* (the "Software"), to deal in the Software without restriction,
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* including without limitation the rights to use, copy, modify, merge,
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* publish, distribute, sublicense, and/or sell copies of the Software,
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* and to permit persons to whom the Software is furnished to do so,
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* subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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#include <asm.h>
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#include <arch/arm/cores.h>
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.text
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.align 2
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.global mymemcpy
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mymemcpy:
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// check for zero length copy or the same pointer
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cmp r2, #0
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cmpne r1, r0
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bxeq lr
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// save a few registers for use and the return code (input dst)
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stmfd sp!, {r0, r4, r5, lr}
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// check for forwards overlap (src > dst, distance < len)
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subs r3, r0, r1
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cmpgt r2, r3
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bgt .L_forwardoverlap
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// check for a short copy len.
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// 20 bytes is enough so that if a 16 byte alignment needs to happen there is at least a
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// wordwise copy worth of work to be done.
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cmp r2, #(16+4)
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blt .L_bytewise
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// see if they are similarly aligned on 4 byte boundaries
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eor r3, r0, r1
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tst r3, #3
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bne .L_bytewise // dissimilarly aligned, nothing we can do (for now)
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// check for 16 byte alignment on dst.
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// this will also catch src being not 4 byte aligned, since it is similarly 4 byte
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// aligned with dst at this point.
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tst r0, #15
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bne .L_not16bytealigned
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// check to see if we have at least 32 bytes of data to copy.
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// if not, just revert to wordwise copy
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cmp r2, #32
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blt .L_wordwise
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.L_bigcopy:
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// copy 32 bytes at a time. src & dst need to be at least 4 byte aligned,
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// and we need at least 32 bytes remaining to copy
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// save r6-r7 for use in the big copy
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stmfd sp!, {r6-r7}
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sub r2, r2, #32 // subtract an extra 32 to the len so we can avoid an extra compare
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.L_bigcopy_loop:
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ldmia r1!, {r4, r5, r6, r7}
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stmia r0!, {r4, r5, r6, r7}
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ldmia r1!, {r4, r5, r6, r7}
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subs r2, r2, #32
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stmia r0!, {r4, r5, r6, r7}
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bge .L_bigcopy_loop
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// restore r6-r7
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ldmfd sp!, {r6-r7}
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// see if we are done
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adds r2, r2, #32
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beq .L_done
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// less then 4 bytes left?
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cmp r2, #4
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blt .L_bytewise
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.L_wordwise:
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// copy 4 bytes at a time.
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// src & dst are guaranteed to be word aligned, and at least 4 bytes are left to copy.
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subs r2, r2, #4
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.L_wordwise_loop:
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ldr r3, [r1], #4
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subs r2, r2, #4
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str r3, [r0], #4
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bge .L_wordwise_loop
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// correct the remaining len and test for completion
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adds r2, r2, #4
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beq .L_done
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.L_bytewise:
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// simple bytewise copy
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ldrb r3, [r1], #1
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subs r2, r2, #1
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strb r3, [r0], #1
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bgt .L_bytewise
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.L_done:
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// load dst for return and restore r4,r5
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#if ARM_ARCH_LEVEL >= 5
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ldmfd sp!, {r0, r4, r5, pc}
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#else
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ldmfd sp!, {r0, r4, r5, lr}
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bx lr
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#endif
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.L_not16bytealigned:
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// dst is not 16 byte aligned, so we will copy up to 15 bytes to get it aligned.
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// src is guaranteed to be similarly word aligned with dst.
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// set the condition flags based on the alignment.
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lsl r12, r0, #28
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rsb r12, r12, #0
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msr CPSR_f, r12 // move into NZCV fields in CPSR
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// move as many bytes as necessary to get the dst aligned
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ldrvsb r3, [r1], #1 // V set
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ldrcsh r4, [r1], #2 // C set
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ldreq r5, [r1], #4 // Z set
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strvsb r3, [r0], #1
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strcsh r4, [r0], #2
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streq r5, [r0], #4
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ldmmiia r1!, {r3-r4} // N set
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stmmiia r0!, {r3-r4}
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// fix the remaining len
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sub r2, r2, r12, lsr #28
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// test to see what we should do now
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cmp r2, #32
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bge .L_bigcopy
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b .L_wordwise
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// src and dest overlap 'forwards' or dst > src
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.L_forwardoverlap:
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// do a bytewise reverse copy for now
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add r1, r1, r2
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add r0, r0, r2
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.L_bytewisereverse:
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// simple bytewise reverse copy
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ldrb r3, [r1], #-1
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subs r2, r2, #1
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strb r3, [r0], #-1
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bgt .L_bytewisereverse
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b .L_done
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