memcpy
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in c++ bekomme ich folgenden fehler:
(uint16_t*)d++; error: ISO C++ forbids incrementing a pointer of type ‘void*’folgendes klappt aber:
(uint16_t*&)d++;wie macht man das in c11?
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der code hat noch einen bug, jemand eine idee wie ich das select fixen kann?
#include <stdio.h> #include <string.h> #include <stdint.h> void *fast_memcpy(void *dst, const void *src, size_t len) { void *d = (void*)dst; void *s = (void*)src; if (len == 0) { return d; } int select = sizeof(uint64_t); switch (select) { case 2: *(uint16_t*)d = *(uint16_t*)s; (uint16_t*)d++; (uint16_t*)s++; len -= sizeof(uint16_t); break; case 4: *(uint32_t*)d = *(uint32_t*)s; (uint32_t*)d++; (uint32_t*)s++; len -= sizeof(uint32_t); break; case 8: *(uint64_t*)d = *(uint64_t*)s; (uint64_t*)d++; (uint64_t*)s++; len -= sizeof(uint64_t); break; default: *(uint8_t*)d = *(uint8_t*)s; (uint8_t*)d++; (uint8_t*)s++; len -= sizeof(uint8_t); break; } return fast_memcpy(d, s, len); } int main(void) { // your code goes here const uint64_t src[] = {12,13,14,15,16}; uint64_t dst[10] = {0}; fast_memcpy(&dst, src, sizeof(src)); for (int i = 0; i < sizeof(src)/sizeof(uint64_t); i++) { printf("%d", (uint32_t)dst[i]); } return 0; }
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int select = sizeof(uint64_t);Das wird halt immer 8 ergeben, auch wenn nur noch 1 byte übrig bleibt.
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ich weiss, copy paste error:
warum klappt das hier nicht? der output ist: 1213000
#include <stdio.h> #include <string.h> #include <stdint.h> void *fast_memcpy(void *dst, const void *src, size_t len) { void *d = (void*)dst; void *s = (void*)src; if (len == 0) { return d; } int select1 = len / sizeof(uint64_t); int select2 = len / sizeof(uint32_t); int select3 = len / sizeof(uint16_t); int select4 = len / sizeof(uint8_t); if (select1 > 0) { *(uint64_t*)d = *(uint64_t*)s; (uint64_t*)d++; (uint64_t*)s++; len -= sizeof(uint64_t); } else if (select2 > 0) { *(uint32_t*)d = *(uint32_t*)s; (uint32_t*)d++; (uint32_t*)s++; len -= sizeof(uint32_t); } else if (select3 > 0) { *(uint16_t*)d = *(uint16_t*)s; (uint16_t*)d++; (uint16_t*)s++; len -= sizeof(uint16_t); } else if (select4 > 0) { *(uint8_t*)d = *(uint8_t*)s; (uint8_t*)d++; (uint8_t*)s++; len -= sizeof(uint8_t); } return fast_memcpy(d, s, len); } int main(void) { // your code goes here const uint64_t src[] = {12,13,14,15,16}; uint64_t dst[10] = {0}; fast_memcpy(&dst, &src, sizeof(src)); for (int i = 0; i < sizeof(src)/sizeof(uint64_t); i++) { printf("%d", (uint64_t)dst[i]); } return 0; }
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rep movs* / rep stos*
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wie meinen? wie kann ich meinen code zum laufen bekommen?
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hi, folgender code funktioniert soweit, ist aber nicht portabel. wie bekomme ich das memory alginment hin?
#include <stdio.h> #include <string.h> #include <stdint.h> void *fast_memcpy(void *dst, const void *src, size_t len) { uint8_t *d = (uint8_t*)dst; uint8_t *s = (uint8_t*)src; if (len == 0) { return d; } int select1 = len % sizeof(uint64_t); int select2 = len % sizeof(uint32_t); int select3 = len % sizeof(uint16_t); if (select1 == 0) { *(uint64_t*)d = *(uint64_t*)s; d+=sizeof(uint64_t); s+=sizeof(uint64_t); len -= sizeof(uint64_t); } else if (select2 == 0) { *(uint32_t*)d = *(uint32_t*)s; d+=sizeof(uint32_t); s+=sizeof(uint32_t); len -= sizeof(uint32_t); } else if (select3 == 0) { *(uint16_t*)d = *(uint16_t*)s; d+=sizeof(uint16_t); s+=sizeof(uint16_t); len -= sizeof(uint16_t); } else { *(uint8_t*)d = *(uint8_t*)s; d+=sizeof(uint8_t); s+=sizeof(uint8_t); len -= sizeof(uint8_t); } return fast_memcpy(d, s, len); } int main(void) { // your code goes here char *src = "cloud"; char dst[10]; fast_memcpy(&dst, src, strlen(src)); for (int i = 0; i < strlen(src); i++) { printf("%c", dst[i]); } return 0; }
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any idea?
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hi,
kann mir jemand feedback zum memory alignment check geben? wie kann ich sowas testen?(uintptr_t)src % sizeof(uint64_t) == 0 && (uintptr_t)dst % sizeof(uint64_t) == 0#include <stdio.h> #include <string.h> #include <stdint.h> void *fast_memcpy(void *dst, const void *src, size_t len) { uint8_t *d = (uint8_t*)dst; uint8_t *s = (uint8_t*)src; if (len == 0) { return d; } bool select1 = len % sizeof(uint64_t); bool select2 = len % sizeof(uint32_t); bool select3 = len % sizeof(uint16_t); if ((uintptr_t)src % sizeof(uint64_t) == 0 && // check memory alignment (uintptr_t)dst % sizeof(uint64_t) == 0 && select1 == 0) { *(uint64_t*)d = *(uint64_t*)s; d+=sizeof(uint64_t); s+=sizeof(uint64_t); len -= sizeof(uint64_t); } else if ((uintptr_t)src % sizeof(uint32_t) == 0 && (uintptr_t)dst % sizeof(uint32_t) == 0 && select2 == 0) { *(uint32_t*)d = *(uint32_t*)s; d+=sizeof(uint32_t); s+=sizeof(uint32_t); len -= sizeof(uint32_t); } else if ((uintptr_t)src % sizeof(uint16_t) == 0 && (uintptr_t)dst % sizeof(uint16_t) == 0 && select3 == 0) { *(uint16_t*)d = *(uint16_t*)s; d+=sizeof(uint16_t); s+=sizeof(uint16_t); len -= sizeof(uint16_t); } else { *(uint8_t*)d = *(uint8_t*)s; d+=sizeof(uint8_t); s+=sizeof(uint8_t); len -= sizeof(uint8_t); } return fast_memcpy(d, s, len); } int main(void) { // your code goes here char *src = "cloud"; char dst[10]; fast_memcpy(&dst, src, strlen(src)+1); for (int i = 0; i < strlen(src); i++) { printf("%c", dst[i]); } return 0; }
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Das könnte dir helfen:
https://www.c-plusplus.net/forum/289488-fullLies dir einfach alles durch auch wenn du nicht asm kannst.
Ansonsten:
https://www.google.de/search?q=fast+memcpy