58 lines
1.9 KiB
C
58 lines
1.9 KiB
C
/* Copyright (C) 2013 - Adam Green (https://github.com/adamgreen)
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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#include <stdio.h>
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#if defined(__GNUC__)
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/* This is a hand written Thumb-2 assembly language version of the
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standard C memcpy() function that can be used by the lwIP networking
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stack to improve its performance. It copies 4 bytes at a time and
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unrolls the loop to perform 4 of these copies per loop iteration.
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*/
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__attribute__((naked)) void thumb2_memcpy(void* pDest, const void* pSource, size_t length)
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{
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__asm (
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".syntax unified\n"
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".thumb\n"
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// Copy 16 bytes at a time first.
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" lsrs r3, r2, #4\n"
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" beq.n 2$\n"
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"1$: ldr r12, [r1], #4\n"
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" str r12, [r0], #4\n"
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" ldr r12, [r1], #4\n"
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" str r12, [r0], #4\n"
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" ldr r12, [r1], #4\n"
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" str r12, [r0], #4\n"
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" ldr r12, [r1], #4\n"
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" str r12, [r0], #4\n"
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" subs r3, #1\n"
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" bne 1$\n"
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// Copy byte by byte for what is left.
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"2$:\n"
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" ands r3, r2, #0xf\n"
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" beq.n 4$\n"
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"3$: ldrb r12, [r1], #1\n"
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" strb r12, [r0], #1\n"
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" subs r3, #1\n"
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" bne 3$\n"
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// Return to caller.
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"4$: bx lr\n"
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);
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}
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#endif
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